GOL 106 LAB 10
A BRIEF SURVEY OF VERTEBRATES (PART 1)
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1 and 2
Precambrian Earth
and
Life History
Part I
(The Archean Eon)
1
Archean Rocks
• The Beartooth Mountains on the Wyoming and Montana
border consists of Archaean-age gneisses
– some of the oldest rocks in the US.
2
Precambrian
• The Precambrian lasted for more than 4 billion
years!
– This large time span is difficult for humans to comprehend
• Suppose that a 24-hour
clock represented all 4.6
billion years of geologic
time then the Precambrian
would be slightly more
than 21 hours long,
constituting about 88% of
all geologic time
3
Precambrian
4
Precambrian
• The term Precambrian is informal but widely
used when referring to both time and rocks
• The Precambrian includes
– time from Earth’s origin 4.6 billion years ago to the
beginning of the Phanerozoic Eon, 542 million
years ago
• It encompasses all rocks below the Cambrian
system
• No rocks are known for the first 600 million
years of geologic time
– The oldest known rocks on Earth are 4.0 billion
years old
5
Rocks Difficult to Interpret
• The earliest record of geologic time preserved in rocks is
difficult to interpret because many Precambrian rocks
have been
•
•
•
•
•
altered by metamorphism
complexly deformed
buried deep beneath younger rocks
fossils are rare, and
the few fossils present are not useful in biostratigraphy
• Subdivisions of the Precambrian have been difficult to
establish
• Two eons for the Precambrian are the Archean and
Proterozoic which are based on absolute ages
6
Eons of the Precambrian
• Eoarchean refers to all time from Earth’s origin to
the Paleoarchean, 3.6 billion years ago
• Earth’s oldest body of rocks, the Acasta Gneiss in
Canada is about 4.0 billion years old
• We have no geologic record for much of the
Archaen
• Precambrian eons have no stratotypes
– unlike the Cambrian Period, for example
7
What Happened
During the Eoarchean?
• Although no rocks of Eoarchean age are present
on Earth,
– except for meteorites,
• We do know some events that took place then
– Earth accreted from planetesimals and differentiated
into core and mantle
• and at least some crust was present
–
–
–
–
Earth was bombarded by meteorites
Volcanic activity was widespread
An atmosphere formed, quite different from today’s
Oceans began to accumulate
8
Hot, Barren, Waterless Early Earth
• about 4.6 billion years ago
• Shortly after accretion, Earth was
–
–
–
–
a rapidly rotating, hot, barren, waterless planet
bombarded by meteorites and comets
with no continents, intense cosmic radiation
and widespread volcanism
9
Oldest Rocks
• Continental crust was present by 4.0 billion
years ago
– Sedimentary rocks in Australia contain detrital
zircons (ZrSiO4) dated at 4.4 billion years old
– so source rocks at least that old existed
• The Eoarchean Earth probably rotated in as
little as 10 hours
– and the Earth was closer to the Moon
• By 4.4 billion years ago, the Earth cooled
sufficiently for surface waters to accumulate
10
Eoarchean Crust
• Early crust formed as upwelling mantle currents
of mafic magma, and numerous subduction zones
developed to form the first island arcs
• Eoarchean continental crust may have formed
– by collisions between island arcs
– as silica-rich materials were metamorphosed.
– Larger groups of merged island arcs
• protocontinents
– grew faster by accretion along their margins
11
Origin of Continental Crust
• Andesitic
island arcs
– form by
subduction
– and partial
melting of
oceanic crust
• The island arc
collides with
another
12
Continental Foundations
• Continents consist of rocks with composition
similar to that of granite
• Continental crust is thicker and less dense than
oceanic crust which is made up of basalt and
gabbro
• Precambrian shields consist of vast areas of
exposed ancient rocks and are found on all
continents
• Outward from the shields are broad platforms of
buried Precambrian rocks that underlie much of
each continent
13
Cratons
• A shield and its platform
make up a craton,
– a continent’s ancient
nucleus
• Along the margins of
cratons, more continental
crust was added as the
continents took their present
sizes and shapes
• Both Archean and Proterozoic rocks are present in
cratons and show evidence of episodes of deformation
accompanied by igneous activity, metamorphism, and
mountain building
• Cratons have experienced little deformation since the
Precambrian
14
Distribution of Precambrian Rocks
• Areas of
exposed
– Precambrian rocks
– constitute
the shields
• Platforms
consist of
– buried Precambrian
rocks
– Shields and adjoining platforms make up cratons
15
Canadian Shield
• The exposed part of the craton in North
America is the Canadian shield
– which occupies most of northeastern Canada
– a large part of Greenland
– parts of the Lake Superior region
• in Minnesota, Wisconsin, and Michigan
– and the Adirondack Mountains of New York
• Its topography is subdued,
– with numerous lakes and exposed Archean and
Proterozoic rocks thinly covered in places by
Pleistocene glacial deposits
16
Evolution of North America
• North America
evolved by the
amalgamation of
Archean cratons
that served as a
nucleus around
which younger
continental crust
was added.
17
Archean Rocks
• Only 22% of Earth’s exposed Precambrian crust is Archean
• The most common Archean rock associations are granitegneiss complexes
• Other rocks range from peridotite to various sedimentary rocks
– all of which have been metamorphosed
• Greenstone belts are subordinate in quantity,
– account for only 10% of Archean rocks
– but are important in unraveling Archean tectonic events
• Outcrop of Archean
gneiss cut by a granite
dike from a granitegneiss complex in
Ontario, Canada
18
Archean Rocks
• Shell Creek in the Bighorn Mountains of Wyoming
has cut a gorge into this 2.9 billion year old granite
19
Archean Plate Tectonics
• Plate tectonic activity has operated since the
Paleoproterozoic or earlier
• Most geologists are convinced that some kind
of plate tectonic activity took place during the
Archean as well
– but it differed in detail from today
• Plates must have moved faster
– with more residual heat from Earth’s origin
– and more radiogenic heat,
– and magma was generated more rapidly
20
Archean Plate Tectonics
• As a result of the rapid movement of plates,
– continents grew more rapidly along their margins, a
process called continental accretion, as plates
collided with island arcs and other plates
• Also, ultramafic extrusive igneous rocks,
– komatites, were more common
21
The Origin of Cratons
• Certainly several small cratons existed during
the Archean and grew by accretion along their
margins
• They amalgamated into a larger unit
– during the Proterozoic
• By the end of the Archean,
– 30-40% of the present volume of continental crust
existed
• Archean crust probably evolved similarly to the
evolution of the southern Superior craton of
Canada
22
Atmosphere and Hydrosphere
• Earth’s early atmosphere and hydrosphere were
quite different than they are now
• They also played an important role in the
development of the biosphere
• Today’s atmosphere is mostly
– nitrogen (N2)
– abundant free oxygen (O2),
• or oxygen not combined with other elements such as in
carbon dioxide (CO2)
– water vapor (H2O)
– small amounts of other gases, like ozone (O3)
• which is common enough in the upper atmosphere to
block most of the Sun’s ultraviolet radiation
23
Present-day
Atmosphere Composition
• Nonvariable gases
Nitrogen N2 78.08%
Oxygen O2 20.95
Argon
Ar
0.93
Neon
Ne
0.002
Others
0.001
• Variable gases
Water vapor H2O
Carbon dioxide CO2
Ozone
O3
Other gases
0.1 to 4.0
0.038
0.000006
Trace
• Particulates
normally trace
in percentage by volume
24
Earth’s Very Early Atmosphere
• Earth’s very early atmosphere was probably
composed of
– hydrogen and helium,
• the most abundant gases in the universe
• If so, it would have quickly been lost into space
– because Earth’s gravity is insufficient to retain them
– because Earth had no magnetic field until its core
formed (magnetosphere)
• Without a magnetic field,
– the solar wind would have swept away any
atmospheric gases
25
Outgassing
• Once a magnetosphere
was present
– Atmosphere began
accumulating as a result of
outgassing, released during
volcanism
• Water vapor is the most
common volcanic gas today
– but volcanoes also emit
carbon dioxide, sulfur
dioxide, carbon monoxide,
sulfur, hydrogen, chlorine,
and nitrogen
26
Archean Atmosphere
• Archean volcanoes probably emitted the same
gases, and thus an atmosphere developed
– but one lacking free oxygen and an ozone layer
• It was rich in carbon dioxide,
– and gases reacting in this early atmosphere
probably formed
• ammonia (NH3)
• methane (CH4)
• This early atmosphere persisted throughout the
27
Archean
Evidence for an
Oxygen-Free Atmosphere
• The atmosphere was chemically reducing
– rather than an oxidizing one
• Some of the evidence for this conclusion comes
from detrital deposits containing minerals that
oxidize rapidly in the presence of oxygen
• pyrite (FeS2)
• uraninite (UO2)
• But oxidized iron becomes increasingly
common in Proterozoic rocks
– indicating that at least some free oxygen was present
then
28
Introduction of Free Oxygen
• Two processes account for introducing free
oxygen into the atmosphere,
• one or both of which began during the Eoarchean.
1. Photochemical dissociation involving ultraviolet
radiation in the upper atmosphere
• The radiation disrupts water molecules and releases their
oxygen and hydrogen
• This could account for 2% of present-day oxygen
• but with 2% oxygen, ozone forms, creating a barrier
against ultraviolet radiation
2. More important were the activities of organisms
that practiced photosynthesis
29
Photosynthesis
• Photosynthesis is a metabolic process
– in which carbon dioxide and water are used in
making organic molecules
– and oxygen is released as a waste product
6CO2 + 6H2O ==> C6H12O6 + 6O2
• Even with photochemical dissociation and
photosynthesis,
– probably no more than 1% of the free oxygen level
of today was present by the end of the Archean
30
Oxygen Forming Processes
• Photochemical dissociation and photosynthesis
added free oxygen to the atmosphere
– Once free
oxygen was
present, an
ozone layer
formed
– and blocked
incoming
ultraviolet
radiation
31
Earth’s Surface Waters
• Outgassing was responsible for the early
atmosphere and also for some of Earth’s surface
water
• the hydrosphere, most of which is in the oceans >
97%
• Another source of our surface water was meteorites and
icy comets
• Numerous erupting volcanoes, and an early episode of
intense meteorite and comet bombardment accounted for
rapid rate of surface water accumulation
32
Ocean Water
• Volcanoes still erupt and release water vapor
– Is the volume of ocean water still increasing?
– Perhaps it is, but if so, the rate has decreased
considerably because the amount of heat needed to
generate magma has diminished
33
Decreasing Heat
• Ratio of radiogenic heat production in the past to
the present
– The width of
the colored
band indicates
variations in
ratios from
different
models
• Heat production
4 billion years
ago was 3 to
6 times as great
as it is now
• With less heat
outgassing
decreased
34
First Organisms
• Today, Earth’s biosphere consists of millions of species
of Archea, Bacteria, Fungi, Protists, Plants, and Animals,
– whereas only bacteria and archea are found in
Archean rocks
• We have fossils from Archean rocks
– 3.5 billion years old
• Chemical evidence in rocks in Greenland that are 3.8
billion years old convince some investigators that
organisms were present then
35
What Is Life?
• Minimally, a living organism must reproduce
– and practice some kind of metabolism
• Reproduction ensures the long-term survival of
a group of organisms
• whereas metabolism maintains the organism
• The distinction between living and nonliving
things is not always easy
• Are viruses living?
– When in a host cell they behave like living
organisms
– but outside, they neither reproduce nor metabolize
36
What Is Life?
• Comparatively simple organic (carbon based)
molecules known as microspheres
– form spontaneously
– can even grow and
divide in a somewhat
organism-like
fashion
– but their processes
are more like random
chemical reactions,
so they are not living
37
How Did Life First Originate?
• To originate by natural processes, from non-living
matter (abiogenesis), life must have passed
through a prebiotic stages
– in which it showed signs of living
– but was not truly living
• The origin of life has 2 requirements
– a source of appropriate elements for organic molecules
– energy sources to promote chemical reactions
38
Elements of Life
• All organisms are composed mostly of
–
–
–
–
carbon (C)
hydrogen (H)
nitrogen (N)
oxygen (O)
• all of which were present in Earth’s early
atmosphere as
–
–
–
–
–
carbon dioxide (CO2)
water vapor (H2O)
nitrogen (N2)
and possibly methane (CH4)
and ammonia (NH3)
39
Basic Building Blocks of Life
• Energy from
• Lightning, volcanism,
• and ultraviolet radiation
– probably promoted chemical reactions during
which C, H, N, and O combined
– to form monomers
• such as amino acids
• Monomers are the basic building blocks of
more complex organic molecules
40
Experiment on the Origin of Life
• Is it plausible that monomers originated in the
manner postulated?
– Experimental evidence indicates that it is
• During the late 1950s
– Stanley Miller
synthesized several
amino acids
– by circulating gases
approximating the early
atmosphere
– in a closed glass vessel
41
Experiment on the Origin of Life
• This mixture was subjected to an electric spark
– to simulate lightning
• In a few days
– it became cloudy
• Analysis showed that
– several amino acids
typical of organisms
had formed
• Since then,
– scientists have
synthesized all 20
amino acids found in
organisms
42
Polymerization
• The molecules of organisms are polymers
– such as proteins
– and nucleic acids
• RNA (ribonucleic acid) and DNA (deoxyribonucleic acid)
consisting of monomers linked together in a specific
sequence
• How did polymerization take place?
• Water usually causes depolymerization,
– however, researchers synthesized molecules known as
proteinoids or thermal proteins
– some of which consist of more than 200 linked amino
acids
– when heating dehydrated concentrated amino acids
43
Proteinoids
• These concentrated amino acids
– spontaneously polymerized to form proteinoids
• Perhaps similar conditions for polymerization
existed on early Earth,
– but the proteinoids needed to be protected by an
outer membrane or they would break down
• Experiments show that proteinoids
spontaneously aggregate into microspheres
– which are bounded by cell-like membranes and
grow and divide much as bacteria do
44
Proteinoid Microspheres
• Proteinoid
microspheres
produced in
experiments
• Proteinoids grow
and divide much as
45
bacteria do
Protobionts
• These proteinoid molecules can be referred to
as protobionts
– These are intermediates between inorganic chemical
compounds and living organisms
46
Monomer and Proteinoid Soup
• The origin-of-life experiments are interesting,
– but what is their relationship to early Earth?
• Monomers likely formed continuously and in
billions
– They accumulated in the early oceans into a “hot,
dilute soup”
– The amino acids in the “soup” might have washed
up onto a beach or perhaps cinder cones
– where they were concentrated by evaporation and
polymerized by heat
• The polymers then washed back into the ocean
– where they reacted further
47
QUESTIONS?
48
Precambrian Earth
and
Life History
Part II
(The Archean Eon)
49
Next Critical Step
• Not much is known about the next critical step in
the origin of life
• the development of a reproductive mechanism
• The microspheres divide and may represent a
protoliving system
– but in today’s cells, nucleic acids,
• either RNA or DNA
– are necessary for reproduction
• The problem is that nucleic acids cannot replicate
without protein enzymes,
– and the appropriate enzymes cannot be made without
nucleic acids,
50
– or so it seemed until fairly recently
RNA World?
• Now we know that small RNA molecules
– can replicate without the aid of protein enzymes
• Thus, the first replicating systems
– may have been RNA molecules
• Some researchers propose
– an early “RNA world” in which these molecules
were intermediate between
• inorganic chemical compounds
• and the DNA-based molecules of organisms
• How RNA was naturally synthesized
– remains an unsolved problem
51
Much Remains to Be Learned
• Scientists agree on some basic requirements for
the origin of life,
– but the exact steps involved and significance of
results are debated
• Many researchers believe that
– the earliest organic molecules were synthesized
from atmospheric gases
– but some scientist suggest that life arose instead near
hydrothermal vents on the seafloor
52
Submarine Hydrothermal Vents
• Seawater seeps into the crust near spreading
ridges, becomes heated, rises and discharges
• Black smokers
– Discharge water
saturated with
dissolved
minerals
– Life may have
formed near these
in the past
53
Submarine Hydrothermal Vents
• Several minerals containing zinc, copper, and iron
precipitate around them
• Communities of organisms
– previously unknown to
science, are supported here.
– Necessary elements, sulfur,
and phosphorus are present in
seawater
– Polymerization can take place
on surface of clay minerals
– Protocells were deposited on
the ocean floor
54
Oldest Known Organisms
• The first organisms were archaea and bacteria
– both of which consist of prokaryotic cells,
– cells that lack an internal, membrane-bounded
nucleus and other structures
• Prior to the 1950s, scientists assumed that life
– must have had a long early history
– but the fossil record offered little to support this idea
• The Precambrian, once called Azoic
– (“without life”), seemed devoid of life
55
Oldest Know Organisms
• Charles Walcott (early 1900s) described structures from
the Paleoproterozoic Gunflint Iron Formation of Ontario, Canada
– that he proposed represented reefs constructed by algae
• Now called
stromatolites,
– not until 1954
were they
shown to be
products of
organic activity
56
Present-day stromatolites (Shark Bay, Australia)
Stromatolites
• Different types of stromatolites include
– irregular mats, columns, and columns linked by mats
57
Stromatolites
• Present-day stromatolites form and grow as
sediment grains are trapped on sticky mats of
photosynthesizing cyanobacteria
– although now they are restricted to environments
where snails cannot live
• The oldest known undisputed stromatolites are
found in rocks in South Africa
– that are 3.0 billion years old
• But probable ones are also known from the Warrawoona
Group in Australia
– which is 3.3 to 3.5 billion years old
58
Other Evidence of Early Life
• Chemical evidence in rocks 3.85 billion years old in
Greenland indicate life was perhaps present then
• The oldest known cyanobacteria were
photosynthesizing organisms
– but photosynthesis is a complex metabolic process
• A simpler type of metabolism must have preceded it
• No fossils are known of these earliest organisms
59
Earliest Organisms
• The earliest organisms must have resembled
– tiny anaerobic bacteria
– meaning they required no oxygen
• They must have totally depended on an external
source of nutrients
– that is, they were heterotrophic, as opposed to
autotrophic organisms
• that make their own nutrients, as in photosynthesis
• They all had prokaryotic cells
60
Earliest Organisms
• The earliest organisms, then, were anaerobic,
heterotrophic prokaryotes
• Their nutrient source was most likely
– adenosine triphosphate (ATP) from their
environment which was used to drive the energyrequiring reactions in cells
• ATP can easily be
synthesized from simple
gases and phosphate
– so it was available in
the early Earth
environment
61
Fermentation
• Obtaining ATP from the surroundings could
not have persisted for long
– because more and more cells competed for the
same resources
• The first organisms to develop a more
sophisticated metabolism
– probably used fermentation to meet their energy
needs
• Fermentation is an anaerobic process in which
molecules such as sugars are split, releasing
carbon dioxide, alcohol, and energy
62
Photosynthesis
• A very important biological event occurring in
the Archean was the development of the
autotrophic process of photosynthesis
• This may have happened as much as 3.5 billion
years ago
• These prokaryotic cells were still anaerobic,
– but as autotrophs they were no longer dependent on
preformed organic molecules as a source of
nutrients
63
Fossil Prokaryotes
• Photomicrographs from western Australia’s
– 3.3- to 3.5-billion-year-old Warrawoona Group,
– with schematic restoration shown at the right of each
64
Archean Mineral Resources
• A variety of mineral deposits are of Archean-age
– but gold is the most commonly associated, although it is
also found in Proterozoic and Phanerozoic rocks
• This soft yellow metal is prized for jewelry,
– but it is or has been used as a monetary standard, in glass
making, electric circuitry, and chemical industry
• About half the world’s gold since 1886 has come from
Archean and Proterozoic rocks in South Africa
• Gold mines also exist in Archean rocks of the Superior
craton in Canada
65
Archean Sulfide Deposits
• Archean sulfide deposits of
• zinc,
• copper
• and nickel
– occur in Australia, Zimbabwe, and in the Abitibi
greenstone belt in Ontario, Canada
• Some, at least, formed as mineral deposits
– next to hydrothermal vents on the seafloor, much as
they do now around black smokers
66
Chrome
• About 1/4 of Earth’s chrome reserves are in
Archean rocks, especially in Zimbabwe
• These ore deposits are found in
– the volcanic units of greenstone belts
– where they appear to have formed when crystals
settled and became concentrated in the lower parts
of plutons
– such as mafic and ultramafic sills
• Chrome is needed in the steel industry
• The United States has very few chrome deposits
– so must import most of what it uses
67
Chrome and Platinum
• One chrome deposit in the United States is in
the Stillwater Complex in Montana
• Low-grade ores were mined there during war
times,
– but they were simply stockpiled and never refined
for chrome
• These rocks also contain platinum,
– a precious metal, that is used
• in the automotive industry in catalytic converters
• in the chemical industry
• for cancer chemotherapy
68
Iron
• Banded Iron formations are sedimentary rocks
– consisting of alternating layers of silica (chert) and
iron minerals
• About 6% of the world’s banded iron
formations were deposited during the Archean
Eon
• Although Archean iron ores are mined in some areas
– they are neither as thick nor as extensive as those of
the Proterozoic Eon, which constitute the world’s
major source of iron
69
Pegmatites
• Pegmatites are very coarsely crystalline igneous
rocks, commonly associated with granite
plutons
• Some Archean pegmatites,
– such in the Herb Lake district in Manitoba, Canada,
– and Rhodesian Province in Africa,
– contain valuable minerals
• In addition to minerals of gem quality,
– Archean pegmatites contain minerals mined for
lithium, beryllium, rubidium, and cesium
70
QUESTIONS?
71
Precambrian Earth
and
Life History
(The Proterozoic Eon – Part I)
1
The Length of the Proterozoic
• The Proterozoic
Eon alone,
– at 1.958 billion
years long,
– accounts for
42.5% of all
geologic time
– yet we review
this long
episode of Earth
and life history
in a single
chapter
2
The Phanerozoic
• The Phanerozoic,
– consisting of
• Paleozoic,
• Mesozoic,
• Cenozoic eras,
– lasted a
comparatively
brief 542 million
years
3
Proterozoic Rocks
• The Vishnu schist in the Grand Canyon was originally
lava flows and sedimentary rocks, but was intruded by
the Zoraster Granite 1.7 billion years ago
4
Proterozoic Rocks
• The outcrop of sandstone and mudstone 1.0 billion years
old has only been slightly altered by metamorphism
5
Archean-Proterozoic Boundary
• Geologists have rather arbitrarily placed the ArcheanProterozoic boundary at 2.5 billion years ago because
it marks the approximate time of changes in the style
of crustal evolution
• However, we must emphasize “approximate”,
because Archean-type crustal evolution was
not completed at the same time in all areas
6
Style of Crustal Evolution
• Archean crust-forming processes generated
– granite-gneiss complexes and greenstone belts
that were shaped into cratons
• Although these same rock associations
continued to form during the Proterozoic,
they did so at a considerably reduced rate
7
Archean vs. Proterozoic
• Many Archean rocks have been metamorphosed,
• However, vast exposures of Proterozoic rocks are
unaltered or nearly so
• In many areas, Archean rocks are separated from
Proterozoic rocks by an unconformity
• Widespread associations of sedimentary rocks of
passive continental margins were deposited during the
Proterozoic by a plate tectonic style essentially the
same as it is now
8
Other Differences
• The Proterozoic was also a time in evolution of
the atmosphere and biosphere as well as the
origin of some important natural resources
• Oxygen-dependent organisms evolved during
this time
• The first multicelled organisms and animals
made their appearance.
• The fossil record is still poor compared to the
9
Phanerozoic
Evolution of
Proterozoic Continents
• Archean cratons assembled during collisions of
island arcs and mini-continents, providing the
nuclei around which Proterozoic crust accreted,
thereby forming much larger landmasses
• Proterozoic accretion
– probably took place more rapidly than today
because Earth possessed more radiogenic heat,
– and the plates moved faster
10
Focus on Laurentia
• Our focus here is on the geologic evolution of
Laurentia, a large landmass that consisted of
what is now
• North America,
• Greenland,
• parts of northwestern Scotland,
• and perhaps some of the Baltic shield of
Scandinavia
11
Early Proterozoic History of
Laurentia
• Laurentia underwent important changes between
2.0 and 1.8 billion years ago
• During this time, collisions among various plates
formed several orogens, which are linear or
arcuate deformation belts in which many of the
rocks have been
• metamorphosed and intruded by magma, thus
forming plutons, especially batholiths
12
Proterozoic Evolution of Laurentia
• Archean cratons were sutured along these
orogens, thereby forming a larger landmass which
makes up much of Greenland, central Canada,
and the north-central United States
13
Wilson Cycle
• Rocks of the Wopmay orogen in northwestern
Canada are important because they record the
opening and closing of an ocean basin or what
is called a Wilson cycle
• A complete Wilson cycle, named after the
Canadian geologist J. Tuzo Wilson, involves
• rifting of a continent,
• opening and closing of an ocean basin,
• and finally reassembly of the continent
14
Wilson Cycle
• Some geologists
think that the
Wopmay orogen
– represents a
complete Wilson
cycle
15
Accretion along Laurentia’s
Southern Margin
• Following the initial episode of amalgamation of
Archean cratons, accretion took place along Laurentia’s
southern margin as it collided with volcanic island arcs
and oceanic terranes
• From 1.65 to 1.76 billion years ago, the Yavapai and
Mazatzal orogens were added to the evolving continent
• The rocks have been deformed, altered by
metamorphism, intruded by granitic batholiths, and
incorporated into Laurentia.
16
Southern Margin Accretion
• Laurentia grew along its southern margin
– by accretion of the Central Plains, Yavapai, and
Mazatzal orogens
17
BIF, Red Beds, Glaciers
• This was also the time during which most of Earth’s
banded iron formations (BIF) were deposited
• The first continental red beds, sandstone and shale
with oxidized iron were deposited
• A significant Paleoproterozoic event was a huge
meteorite impact that took place in northern
Ontario, Canada
• In addition, some Early Proterozoic rocks and
associated features provide excellent evidence for
widespread glaciation
18
Mesoproterozoic Accretion &
Igneous Activity
• During the interval from 1.35 to 1.55 billion years ago,
extensive igneous activity took place
– that seems to be unrelated to orogenic activity and
accounted for the addition of the Granite-Rhyolite
province
• Some of the igneous activity resulted in plutons being
emplaced in existing continental crust.
• The resulting igneous rocks are exposed in eastern Canada
extend across Greenland, and are also found in the Baltic
Shield, Scandinavia
19
Grenville Orogeny
• Rocks of the Grenville Orogen
– These metamorphic rocks are uncomformably
overlain by the Upper Cambrian Potsdam Formation.
20
Sedimentary
Basins in the West
• Meso- to
Neoproterozoic basin
– in the western United
States and Canada
• Belt Basin
• Uinta Basin
• Apache Basin
21
Sedimentary Rocks
• Meso- and Neoproterozoic sedimentary rocks are
exceptionally well exposed in the northern Rocky
Mountains of Montana and Alberta, Canada
• Indeed, their colors, deformation features, and
erosion by Pleistocene and recent glaciers have
yielded some fantastic scenery
• Like the Paleo-proterozoic rocks in the Great
Lakes region, they are mostly sandstones, shales,
and stromatolite-bearing carbonates
22
Belt Basin, Glacier National Park
• Meso- and Neoproterozoic rocks in the Belt basin
23
Proterozoic Sandstone
• Proterozoic rocks of the Grand Canyon Supergroup lie unconformably upon Archean rocks
– and in turn are overlain unconformably by
Phanerozoic-age rocks
• The rocks, consisting mostly of sandstone,
shale, and dolostone, were deposited in shallowwater marine and fluvial environments
• The presence of stromatolites and carbonaceous
impressions of algae in some of these rocks
indicate probable marine deposition
24
Grand Canyon Super-group
• Neoproterozoic sandstone in the Grand Canyon
25
Proterozoic Supercontinents
• A continent is a landmass made up of granitic
crust with much of its surface above sea level
• A supercontinent consists of at least two
continents merged into one, but usually
includes all or most of all Earth’s landmasses
• The supercontinent Pangaea, which existed at
the end of the Paleozoic Era, is familiar,
– but few people are aware of earlier supercontinents
26
Early Supercontinents
• Supercontinents may have existed as early as
the Neoarchean,
– but if so we have little evidence of them
• The first that geologists recognize with some
certainty, known as Rodinia, assembled
between 1.3 and 1.0 billion years ago
– and then began fragmenting 750 million years ago
27
Early Supercontinent (Rodinia)
• Possible
configuration of
the Neoproterozoic
supercontinent
Rodinia
– before it began
fragmenting about
750 million years
ago
28
Early Supercontinent (Pannotia)
• Judging by the Pan-African orogeny and the large-scale
deformation that took place in what are now the
Southern Hemisphere continents, Rodinia’s separate
pieces reassembled and formed another supercontinent
– Pannotia, about 650 million years ago
• Fragmentation was underway again, by the latest
Proterozoic, about 550 million years ago, giving rise to
the continental configuration
– that existed at the onset of the Phanerozoic Eon
29
Ancient Glaciers
• Very few instances of widespread glacial
activity have occurred during Earth history
• The most recent one during the Pleistocene 1.8
million to 10,000 years ago is the best known,
– but we also have evidence for Pennsylvanian
glaciers and two major episodes of Proterozoic
glaciation
30
Recognizing Glaciation
• How can we be sure that there were
Proterozoic glaciers?
– Their most common deposit, called tillite, is simply
a type of conglomerate/breccia that may look much
like conglomerates originating from other
processes
• Tillite or tillite-like deposits are known from at
least 300 Precambrian localities, and some of
these are undoubtedly not glacial deposits
31
Proterozoic Glacial Evidence
• Tillite in Norway
– overlies striated bedrock surface of sandstone
32
Geologists Convinced
• Geologists are now convinced, based on this kind
of evidence, that widespread glaciation took
place during the Paleoproterozoic
• The occurrence of tillites
of about the same age in
Michigan, Wyoming,
and Quebec indicates
that North America may
have had an ice sheet
centered southwest of
Hudson Bay
33
Snowball Earth?
• Some geologists think that glaciers covered all land and
all seas were frozen
– a snowball Earth
• This hypothesis is controversial but proponents claim
that onset of this glacial episode may have been triggered
by the near-equatorial location of the continents
– Accelerated weathering would absorb huge quantities
of CO2
– With little CO2 glaciers would form and reflect solar
radiation back into space, forming more glacier 34
Snowball Earth?
• Volcanoes would continue spewing gases, which
would warm the atmosphere and end the glacial
episode
• One criticism of the snowball Earth hypothesis:
How would life survive?
– Suggestions include
•
•
•
•
Life persisted at hydrothermal vents on the seafloor
Photosynthesis can take place beneath thin glacial ice
Life may have persisted in sub-glacial lakes
There may have been pools of water near volcanoes
35
The Evolving Atmosphere
• Geologists agree that the Archean atmosphere
– contained little or no free oxygen so the atmosphere
was not strongly oxidizing as it is now
• Even though processes were underway that added
free oxygen to the atmosphere, the amount
present at the beginning of the Proterozoic was
probably no more than 1% of that present now
• In fact, it might not have exceeded 10% of
present levels even at the end of the Proterozoic
36
Cyanobacteria and Stromatolites
• Remember that cyanobacteria, were present
during the Archean, but stromatolites
• the structures they formed,
– did not become common until about 2.3 billion
years ago,
• that is, during the Paleoproterozoic
• These photosynthesizing organisms
– and to a lesser degree, photochemical dissociation
• added free oxygen to the evolving atmosphere
37
Oxygen Versus Carbon Dioxide
• Earth’s early atmosphere had abundant carbon
dioxide
• More oxygen became available whereas the
amount of carbon dioxide decreased
• Only a small amount of CO2 still exists in the
atmosphere today
• It is one of the greenhouse gases
– partly responsible for global warming
38
Life of the Proterozoic
• Archean fossils are not very common, and consists
of archea and bacteria, although there were many
types of these organisms
• Likewise, the Paleoproterozoic fossil record is
characterized by the same organisms although
stromatolites became common
• The lack of biotic diversity is not surprising
because prokaryotic cells reproduce asexually and
do not share their genetic material
– so evolution is a comparatively slow process.
39
Gunflint Microfossils
• Proterozoic microfossils from the Gunflint Iron
Formation of Canada, resemble bacteria living today
40
Precambrian Earth
and
Life History
(The Proterozoic Eon – Part II)
41
Stromatolites
• Two Proterozoic stromatolites had grown together
42
Sexual Reproduction Increased
the Pace of Evolution
• Organisms that reproduced sexually probably
evolved by the Mesoproterozoic, and the tempo
of evolution increased markedly
– though from our perspective it was still
exceedingly slow.
43
Eukaryotic Cells
• Eukaryotic cells are much larger than prokaryotic
cells
– have an internal membrane-bound nucleus and other
internal structures not found in prokaryotes
• Many eukaryotes are multi-celled and aerobic
– Most of them reproduce sexually
• Although 6 kingdoms are recognized,
– only 3 domains of living things exits
– Two domains are prokaryotic, and the other is
eukaryotic
44
Prokaryotic Cell
• Prokaryotic cells
– do not have a cell nucleus
– do not have organelles
– are smaller and not nearly as complex as eukaryotic
cells
45
Eukaryotic Cell
• Eukaryotic cells have
– a cell nucleus
containing
– the genetic material
– and organelles
– such as mitochondria
– and plastids,
– as well as chloroplasts
in plant cells
46
Domains of Life
• The inferred relationship among these organisms
are based on analyses of a type of ribosomal RNA
– Eukarya is more closely related to the archaea than to
bacteria
47
Eukaryotic Fossil Cells
• The oldest known eukaryotes are found in 1.2 billion year
Mesoproterozoic rocks in Canada
– These tiny organisms, Bangiomorpha,
• were single celled
• probably reproduced sexually
• and resemble red algae.
• The 2.1 billion year Negaunee Iron Formation has fossils
– but these megafossils were likely single-celled bacteria
– or some kind of algae.
48
Oldest Eukaryotes
• At 1.2 billion
years,
Bangiomorpha
is the oldest
known
eukaryote.
49
Oldest Eukaryotes
• Grypania, at 2.1 billion years, is the oldest
known megafossil.
– It was probably a bacterium or
– some kind
of algae.
50
Acritarchs
• Cells larger than 60 microns appear at least 1.4 billion
years ago
– and many of them show an increase in organizational
complexity
– An internal membrane-bounded nucleus is present in
some
• Hollow fossils known as acritarchs
– were probably cysts of planktonic algae
– and became common during the Meso- and
Neoproterozoic
51
Acritarchs
• These Proterozoic fossils are probably from
eukaryotic organisms
• Acritarchs are very likely the cysts of algae
52
Endosymbiosis and the
Origin of Eukaryotic Cells
• Eukaryotic cells probably formed from
prokaryotic cells that entered into a symbiotic
relationship
– Symbiosis,
• involving a prolonged association of two or more
dissimilar organisms, is common today
• In many cases both symbionts benefit from the
association
– as occurs in lichens,
• once thought to be plants
• but actually symbiotic fungi and algae
53
Endosymbiosis
• An aerobic bacterium and a larger host bacterium
united to form a mitochondria-containing amoeboid.
54
Endosymbiosis
• In a symbiotic relationship, each symbiont is
usually capable of metabolism and
reproduction,
– but the degree of dependence in some relationships
• is such that one or both symbionts cannot live
independently
• This may have been the case with Proterozoic
symbiotic prokaryotes
– that became increasingly interdependent until the
unit could exist only as a whole
• In this relationship
– one symbiont lived within the other, which is a
special type of symbiosis called endosymbiosis
55
Multicelled Organisms
• Multicelled organisms are made up of many
cells, with cells specialized to perform specific
functions
– such as reproduction and respiration
• Multicelled organisms were present by the
Neoproterozoic
– but the fossil record does not show the transition
56
Multicelled Organisms
• Some living organisms,
– while multicelled
– possess as few as four identical cells
– all of which are capable of living on their own.
57
The Multicelled Advantage?
• Is there any particular advantage to
being multicelled?
• For something on the order of 1.5
billion years
– all organisms were single-celled
– and life seems to have thrived
• In fact, single-celled organisms
– are quite good at what they do
– but what they do is very limited
58
The Multicelled Advantage?
• For example, single celled organisms
– can not grow very large, because as size increases,
proportionately less of a cell is exposed to the
external environment in relation to its volume
– and the proportion of surface area decreases
• Transferring materials from the exterior to the
interior becomes less efficient
59
The Multicelled Advantage?
• Also, multicelled organisms live longer,
– because cells can be replaced and more offspring
can be produced
• Cells have increased functional efficiency when
they are specialized into organs with specific
functions
60
Neoproterozoic Animals
• Biologists set forth criteria such as
– method of reproduction and type of metabolism
– to allow us to easily distinguish between animals
and plants
• Or so it would seem,
– but some present-day organisms blur this
distinction—and the same is true for some
Proterozoic fossils
• Nevertheless, the first relatively controversyfree fossils of animals come from the Ediacaran
fauna of Australia
– and similar faunas of similar age elsewhere
61
Ediacaran Fauna
• The Ediacaran fauna of Australia
Tribrachidium heraldicum, a possible primitive
echinoderm or cnidarian
Spriggina floundersi, a possible
ancestor of trilobites
62
Ediacaran Fauna
Parvanconrina is
perhaps related to
arthropods
• Restoration of the
Ediacaran Environment
63
Represented Phyla
• Three present-day phyla may be represented
– in the Ediacaran fauna:
• jellyfish and sea pens (phylum Cnidaria),
• segmented worms (phylum Annelida),
• and primitive members of the phylum Arthropoda (the
phylum with insects, spiders crabs, and others)
• One Ediacaran fossil, Spriggina,
– has been cited as a possible ancestor of trilobites
• Another might be a primitive member
– of the phylum Echinodermata
64
Other Proterozoic Animal Fossils
• Although scarce, a few animal fossils older
than those of the Ediacaran fauna are known
• A jellyfish-like impression is present in rocks
2000 m below the Pound Quartzite
• Burrows, in many areas, presumably made by
worms, are found in rocks at least 700 million
years old
• Some possible fossil worms are found
– from 700- to 900 million-year-old rocks in China65
Wormlike Fossils from China
• Wormlike
fossils from
Late
Proterozoic
rocks in China
66
Proterozoic Mineral Resources
• Most of the world’s iron ore comes from
– Paleoproterozoic banded iron formations
• Canada and the United States have large
deposits of these rocks
– in the Lake Superior region and in eastern Canada
• Thus, both countries rank among
– the ten leading nations in iron ore production
67
Iron Mine
• The Empire Mine at Palmer, Michigan
– where iron ore from the Paleoproterozoic
Negaunee Iron Formation is mined
68
Nickel
• In the Sudbury mining district in Ontario,
Canada,
– nickel and platinum are extracted from Proterozoic
rocks
• Nickel is essential for the production of nickel
alloys such as
• stainless steel
• and Monel metal (nickel plus copper),
– which are valued for their strength and resistance to
corrosion and heat
• The United States must import more than 50%
of all nickel used mostly from the Sudbury
mining district
69
Platinum and Chromium
• Some platinum for jewelry, surgical
instruments, and chemical and electrical
equipment is exported to the United States from
Canada,
– but the major exporter is South Africa
• The Bushveld Complex of South Africa is a
layered igneous complex containing both
• platinum
• and chromite
– the only ore of chromium,
– United States imports much of the chromium from
South Africa
– It is used mostly in stainless steel
70
Oil and Gas
• Economically recoverable oil and gas have
been discovered in Proterozoic rocks in China
and Siberia, arousing some interest in the
Midcontinent rift as a potential source of
hydrocarbons
• So far, land has been leased for exploration, and
numerous geophysical studies have been done
• However, even though some rocks within the
rift are known to contain petroleum,
– no producing oil or gas wells are operating
71
Proterozoic Pegmatites
• A number of Proterozoic pegmatites are
important economically
• The Dunton pegmatite in Maine, whose age is
generally considered to be Neoproterozoic,
– has yielded magnificent gem-quality specimens of
tourmaline and other minerals
• Other pegmatites are mined for gemstones, tin,
industrial minerals, such as feldspars, micas,
and quartz
– and minerals containing such elements as cesium,
rubidium, lithium, and beryllium
72
Proterozoic Pegmatites
• Geologists have identified more than 20,000
pegmatites in the country rocks adjacent to the
Harney Peak Granite
– in the Black Hills of South Dakota
• These pegmatites formed ~ 1.7 billion years ago
– when the granite was emplaced as a complex of
dikes and sills
• A few have been mined for gemstones, tin,
lithium, micas,
– and some of the world’s largest known mineral
crystals were discovered in these pegmatites
73
QUESTIONS?
74
Chapter 19
Primate and Human Evolution
Part I
1
The Cradle of Mankind
• Olduvai Gorge on the eastern Serengeti Plain, Northern
Tanzania
– is often referred to as “The Cradle of Mankind”
• because of many important hominid discoveries there
2
Who are we?
•
•
•
•
Who are we?
Where did we come from?
What is the human genealogy?
These are basic questions
– that we probably have all asked ourselves
3
Back Farther
Than We Thought
• Just as many people enjoy tracing their own
family history as far back as they can,
– paleoanthropologists are discovering, based on
recent fossil finds,
– that the human family tree goes back much farther
than we thought
4
Hope of Life
• In fact, a skull found in the African nation of
Chad, in 2002 and named Sahelanthropus
tchadensis
• but nicknamed Tourmaï,
• which means “hope of life” in the local Goran language,
– has pushed back the origins of humans to nearly 7
million years ago
• Another discovery reported in 2006
– provides strong evidence for an ancestordescendant relationship between two early hominid
lines,
• one of which leads to our own human lineage
5
Understanding in Flux
• So where does this leave us, evolutionarily
speaking?
– At a very exciting time, as we seek to unravel the
history of our species
• Our understanding of our genealogy
– is presently in flux,
– and each new fossil hominid find
– sheds more light on our ancestry
6
Human Evolution
• Human evolution is just like that of other groups
• We have followed an uncertain evolutionary path
• As new species evolved, they filled ecologic
niches and gave rise to descendants better
adapted to the changing environment
– or they became extinct
• Our own evolutionary history has many “deadend” side branches
7
New Hypotheses About
Our Ancestry
• We examine the various primate groups,
– in particular the origin and evolution of the
hominids, the group that includes our ancestors
• However, we must point out
– that new discoveries of fossil hominids,
– as well as new techniques for scientific analysis
– are leading to new hypotheses about our ancestry
8
Continuing Discoveries
Change Our Ideas
• New discoveries may change
– some of the conclusions stated here
• Such is the nature of paleoanthropology—
– and one reason the study of hominids is so exciting
9
What Are Primates?
• Primates are difficult to characterize as an
order
– because they lack the strong specializations found
in most other mammalian orders
• We can, however, point to several trends
– in their evolution that help define primates
– and are related to their arboreal, or tree-dwelling,
ancestry
10
Trends in Primates
• These include changes in the skeleton
– and mode of locomotion,
– an increase in brain size,
– a shift toward smaller, fewer, and less specialized
teeth,
– and the evolution of stereoscopic vision
– and a grasping hand with opposable thumb
• Not all these trends took place in every primate
group,
– nor did they evolve at the same rate in each group
11
Variations
• In fact, some primates
– have retained certain primitive features,
– whereas others show all or most of these trends
12
Classification of Primates
• The primate order is divided into two suborders
– Prosimii and Anthropoidea
• The prosimians, or lower primates,
– include the lemurs, lorises, tarsiers, and tree
shrews,
• while the anthropoids, or higher primates,
– include monkeys, apes, and humans
13
Classification of Primates
• Order Primates:
– Suborder Prosimii: (lower primates) Lemurs,
lorises, tarsiers, tree shrews
– Suborder Anthropoidea: (Higher primates)
Monkeys, apes, humans
• Superfamily Cercopithecoidea: Macaque, baboon,
proboscis monkey (Old World monkeys)
• Superfamily Ceboidea: Howler, spider and squirrel
monkeys (New World monkeys)
• Superfamily Hominoidea: (Apes, humans)
– Family Pongidae: Chimpanzees, orangutans, gorillas
– Family Hylobatidae: Gibbons, siamangs
– Family Hominidae: Humans
14
Prosimians
• Prosimians are generally small,
– ranging from species the size of a mouse
– up to those as large as a house cat
• They are arboreal, have five digits
– on each hand and foot
– with either claws or nails,
– and are typically omnivorous
• They have large, forwardly directed eyes
– specialized for night vision,
– hence most are nocturnal
15
Tarsier
• Tarsiers are
prosimian
primates
16
Prosimians
• As their name implies
• pro means “before,” and simian means “ape”,
– prosimians are the oldest primate lineage,
– and their fossil record extends back to the Paleocene
• During the Eocene, prosimians were
– abundant, diversified, and widespread in North
America, Europe, and Asia
17
Eocene Prosimian
• Notharctus, a primitive Eocene prosimian
– from
North
America
18
Prosimians Declined in Cooler
Climate
• As the continents moved northward during the
Cenozoic
– and the climate changed from warm tropical to
cooler mid-latitude conditions,
– the prosimian population decreased in both
abundance and diversity
19
Prosimians Are Tropical
• By the Oligocene, hardly any prosimians
– were left in the northern continents
– as the once widespread Eocene populations
migrated south to the warmer latitudes
– of Africa, Asia, and Southeast Asia
• Presently, prosimians are found
– only in the tropical regions
– of Asia, India, Africa, and Madagascar
20
Anthropoids
• Anthropoids evolved from a prosimian lineage
– sometime during the Late Eocene,
– and by the Oligocene they were a well-established
group
• Anthropoids are divided into three superfamilies
21
New World Monkey: Spider
Monkey
• New World Monkeys constitute a
superfamily belonging to the suborder
Anthropoidea (anthropoids)
22
Old World Monkey: Baboon
• Another
superfamily of the
anthropoids:
• the Old World
monkeys
23
Hominoids: Chimpanzees
• The
hominoids,
include apes
and humans
24
Early History of Anthropoids
• Much of our knowledge about the early
evolutionary history of anthropoids comes from
fossils found in the Fayum district,
– a small desert area southwest of Cairo, Egypt
• During the Late Eocene and Oligocene,
– this region of Africa was a lush, tropical rain forest
– that supported a diverse and abundant fauna and
flora
• Within this forest lived many different
– arboreal anthropoids as well as various prosimians
25
Thousands of Fossil Specimens
• In fact, several thousand fossil specimens
• representing more than 20 species of primates
– have been recovered from rocks of this region
• One of the earliest anthropoids,
– was Aegyptopithecus,
• a small, fruit-eating, arboreal primate, about 5 kg
– It had monkey characteristics and ape features
• and is the closest link we currently have to Old World
primates
26
One of the Earliest Anthropoids
• Skull of
Aegyptopithecus
zeuxis,
– one of the earliest
known anthropoids
27
Anthropoid Superfamilies
• Anthropoids are divided into three
superfamilies
– Cercopithecoidea (Old World monkeys),
– Ceboidea (New World monkeys),
– Hominoidea (apes and humans)
28
Old World Monkey Attributes
• Old World monkeys
• superfamily Cercopithecoidea
– include the macaque, baboon, and proboscis monkey
– They are characterized
by close-set, downwarddirected nostrils
• like those of apes and
humans
– grasping hands, and a
non-prehensile tail
29
Old Word Monkey
• Superfamily
Cercopithecoidea
• the Old World monkeys
30
Old World Monkeys Distribution
• Present-day Old World monkeys
– are distributed in the tropical regions of Africa and
Asia
– and are thought to have evolved from a primitive
anthropoid ancestor, like Aegyptopithecus,
– sometime during the Oligocene
31
New World Monkeys
• New World monkeys
• superfamily Ceboidea
– are found only in Central and
South America
• They are characterized
– by a prehensile tail, flattish
face, and widely separated
nostrils
– and include the howler,
spider, and squirrel monkeys
32
New World Monkey
• New World
Monkeys are
members of the
superfamily
Ceboidea
33
No Contact
• New World monkeys probably evolved from
African monkeys
–
–
–
–
that migrated across the widening Atlantic
sometime during the Early Oligocene,
and they have continued evolving in isolation
to this present day
• No evidence exists of any prosimian
– or other primitive primates in Central or South
America
– nor of any contact with Old World monkeys after
the initial immigration from Africa
34
Hominoids
• Hominoids
– superfamily Hominoidea
• consist of three families:
– the great apes
• family Pongidae
• which includes chimpanzees, orangutans, and gorillas
– the lesser apes
• family Hylobatidae
• which are gibbons and siamangs;
– and the hominids
• family Hominidae
• which are humans and their extinct ancestors
35
Hominoid Lineage
• The hominoid lineage
– diverged from Old World monkeys
– sometime before the Miocene,
– but the exact time is still being debated
• It is generally accepted, however,
– that hominoids evolved in Africa,
– probably from the ancestral group that included
Aegyptopithecus
36
Climatic Shifts
• Recall that beginning in the Late Eocene
– the northward movement of the continents resulted
in pronounced climatic shifts
• In Africa, Europe, Asia, and elsewhere,
– a major cooling trend began,
– and the tropical and subtropical rain forests slowly
began to change to a variety of mixed forests
– separated by savannas and open grasslands as
temperatures and rainfall decreased
37
Apes Adapted
• As the climate changed,
– the primate populations also changed
• Prosimians and monkeys became rare,
– whereas hominoids diversified in the newly
forming environments
– and became abundant
• Ape populations became reproductively
isolated from each other within the various
forests,
– leading to adaptive radiation and increased
diversity among the hominoids
38
Migration of Animals Possible
• During the Miocene,
– Africa collided with Eurasia, producing additional
changes in the climate
– as well as providing opportunities for migration of
animals between the two landmasses
39
Hominoid Relationships
• Two apelike groups evolved during the
Miocene
– that ultimately gave rise to present-day hominoids
• Although there is still not agreement
– on the early evolutionary relationships among the
hominoids,
– fossil evidence and molecular DNA similarities
between modern hominoid families is providing a
clearer picture of the evolutionary pathways
– and relationships among the hominoids
40
Dryopithecines
• The first group, the dryopithecines,
– evolved in Africa during the Miocene
– and subsequently spread to Eurasia,
– following the collision between the two continents
• The dryopithecines were a group of hominoids
that varied
– in size,
– skeletal features,
– and life-style
41
Proconsul
• The best-known dryopithecine and perhaps
– ancestor of all later hominoids is Proconsul,
• an ape-like fruit-eating animal
• that led a quadrupedal arboreal existence,
• with limited activity on the ground
• The dryopithecines were very abundant
– and diverse during the Miocene and Pliocene,
– particularly in Africa
42
Proconsul
• Probable appearance of Proconsul, a
dryopithecine
43
Sivapithecids
• The second group, the sivapithecids,
– evolved in Africa during the Miocene
– and then spread throughout Eurasia
• The fossil remains of sivapithecids
– consist mostly of jaws, skulls, and isolated teeth
• Body or limb bones are rare,
– limiting our knowledge about what they looked like
– and how they moved around
44
Sivapithecids Ate Harder Foods
• Sivapithecids had powerful jaws
– and thick-enameled teeth with flat chewing
surfaces,
– suggesting a diet of harder foods such as nuts
• It is clear from fossil evidence,
– the sivapithecids were not involved in the
evolutionary branch leading to humans,
– but were probably the ancestral stock from which
present-day orangutans evolved
– In fact, one early genus, Gigantopithecus, was a
contemporary of early Homo in Eastern Asia 45
Two Lineages
• Although many pieces are still missing,
–
–
–
–
–
particularly during critical intervals
in the African hominoid fossil record,
molecular DNA as well as fossil evidence indicates
that the dryopithecines, African apes, and hominids
form a closely related lineage
• The sivapithecids and orangutans
– form a different lineage that did not lead to humans
46
Hominids
• The hominids (family Hominidae)
–
–
–
–
the primate family that includes present-day humans
and their extinct ancestors
have a fossil record extending back
to almost 7 million years
• Several features distinguish them from other
hominoids
• Hominids are bipedal;
– that is, they have an upright posture,
– which is indicated by several modifications in their
skeleton
47
Comparison of Locomotion
• Comparison between
quadrupedal and
bipedal locomotion
– in gorillas and humans
• In gorillas the ischium
bone is long
– and the entire pelvis is
tilted toward the
horizontal
48
Comparison of Locomotion
• Comparison between
quadrupedal and
bipedal locomotion
– in gorillas and humans
• In humans the ischium
bone is much shorter
• and the pelvis is vertical
49
Larger Reorganized Brain
• In addition, hominids show a trend toward a
large and internally reorganized brain
• An increase in
brain size and
organization
– is apparent in
comparing the
brains of
– a New World
Monkey
50
Larger Reorganized Brain
– a Great Ape
– a present-day
Human
51
Other Distinguishing Features
• Other features that distinguish hominids from
other hominoids include
–
–
–
–
a reduced face and reduced canine teeth,
omnivorous feeding,
increased manual dexterity,
and the use of sophisticated tools
52
Response to Climatic Changes
• Many anthropologists think
– these hominid features evolved in response to
major climatic changes
– that began during the Miocene and continued into
the Pliocene
• During this time, vast savannas replaced the
African tropical rain forests
– where the lower primates and Old World monkeys
had been so abundant
53
Mixed Forests and Grasslands
• As the savannas and grasslands continued to
expand,
– the hominids made the transition from true forest
dwelling to life to an environment of mixed forests
and grasslands
54
No Clear Consensus
• At present, no clear consensus exists
– on the evolutionary history of the hominid lineage
• This is due, in part,
– to the incomplete fossil record of hominids
– as well as new discoveries,
– and also because some species are known only
from partial specimens or fragments of bone
• Because of this, there is even disagreement
– on the total number of hominid species
55
Some Current Theories
• A complete discussion of all the proposed
hominid species and the various competing
schemes of hominid evolution is beyond the
scope of this course
• However, we will discuss the generally
accepted taxa
– and present some of the current theories of hominid
evolution
56
Stratigraphic Record
• The geologic ranges
– for the commonly accepted species of hominids
57
Debates
• Remember that although the fossil record of
hominid evolution is not complete,
– what exists is well documented
• Furthermore, the interpretation of that fossil
record
– precipitates the often vigorous and sometimes
acrimonious debates concerning our evolutionary
history
58
Oldest Known Hominid
• Discovered in northern Chad’s Djurab Desert
–
–
–
–
–
in July 2002,
the nearly 7-million-year-old skull
and dental remains of Sahelanthropus tchadensis
make it the oldest known hominid yet unearthed
and at or near to the time when humans diverged
from our closest-living relative, the chimpanzee
59
Sahelanthropus tchadensis
• Discovered in
Chad in 2002
• and dated at
nearly 7 million
years,
• this skull is
presently the
oldest known
hominid
60
When Humans and Chimpanzees
Diverged
• Currently, most paleoanthropologists accept
– that the human-chimpanzee stock separated from
gorillas about 8 million years ago
– and humans separated from chimpanzees about 5
million years ago
61
Oldest Hominid
• Besides being the oldest hominid,
– Sahelanthropus tchadensis shows a mosaic of
primitive and advanced features that has both
excited and puzzled paleoanthropologists
• Its small brain case and most of its teeth (except
the canines) are chimplike
• However, the nose, which is fairly flat, and the
prominent brow ridges are features only seen,
until now,
– in the human genus Homo
62
QUESTIONS?
63
Chapter 19
Primate and Human Evolution
Part II
64
Leg Bones and Feet Needed
• It is hypothesized that Sahelanthropus
tchadensis was probably bipedal in its walking
habits,
– but until bones from its legs and feet are found,
– that supposition remains inconclusive
65
Next Oldest Hominid
• The next oldest hominid is Orrorin tugenensis,
– whose fossils have been dated at 6 million years
– and consist of bits of jaw, isolated teeth, finger,
arm, and partial upper leg bones
• At this time, debate continues as to exactly
where Orrorin tugenensis fits in the hominid
lineage
66
Ardipithecus ramidus
• Sometime between 5.8 and 5.2 million years
ago, another hominid was present in eastern
Africa
• Ardipithecus ramidus kadabba is older than its
4.4 million year old relative Ardipithecus
ramidus ramidus
• Ardipithecus ramidus kadabba is very similar
in most features to Ardipithecus ramidus
ramidus
– but in specific features of its teeth is more apelike
67
than its younger relative
Stratigraphic Record
• The geologic age ranges
– for the commonly accepted species of hominids
68
Habitual Bipedal Walkers
• Although many paleoanthropologists think
– both Orrorin tugenensis and Ardipithecus ramidus
kadabba were habitual bipedal walkers and thus on
a direct evolutionary line to humans,
– others are not as impressed with the fossil evidence
and are reserving judgment
• Until more fossil evidence is found and
analyzed,
– any single scheme of hominid evolution presented
here would be premature
69
Australopithecines
• Australopithecine is a collective term
– for all members of the genus Australopithecus
• Currently, five species are recognized:
–
–
–
–
–
A. anamensis,
A. afarensis,
A. africanus,
A. robustus,
A. boisei
70
Evolutionary Scheme
• Many paleontologists accept the evolutionary
scheme in which
– A. anamensis,
• the oldest known australopithecine,
– is ancestral to A. afarensis,
• who in turn is ancestral to A. africanus, and the genus
Homo,
• as well as the side branch of australopithecines
represented by A. robustus and A. boisei
71
Oldest Known Australopithecine
• The oldest known australopithecine is
Australopithecus anamensis
– discovered at Kanapoi,
• a site near Lake Turkana, Kenya,
– by Meave Leakey
• of the National Museums of Kenya
– and her colleagues
72
Similar Yet More Primitive
• A. anamensis, a 4.2-million-year-old bipedal
species,
– has many features in common with its younger
relative, A. afarensis,
– yet is more primitive in other characteristics, such as
its teeth and skull
• A. anamensis
– is estimated to have been between 1.3 and 1.5 m tall
– and weighed 33 to 50 kg
73
New Fossil Discovery
• A discovery, reported in 2006, of fossils
– of A. anamensis, from the Middle Awash area
• in northeastern Ethiopia
– has shed new light on the transition between
– Ardipithecus and Australopithecus.
• The discovery of Ardipithecus in the same
region of Africa and same times as the earliest
Australopithecus provides strong evidence that
Ardipithecus evolved into Australopithecus
– and links these two genera in the evolutionary
lineage leading to humans
74
Australopithecus afarensis
• Australopithecus afarensis, who lived 3.9–3.0
million years ago,
– was fully bipedal
– and exhibited great variability in size and weight
• Members of this species ranged
– from just over 1 m to about 1.5 m tall
– and weighed between 29 and 45 kg
75
Lucy
• A reconstruction of Lucy’s
skeleton by Owen Lovejoy
• and his students at Kent State
University, Ohio
• Lucy is an ~ 3.5-millionyear-old
– Australopithecus afarensis
This reconstruction illustrates how
adaptations in
• Lucy’s hip, leg and foot
• allowed a fully bipedal means of
locomotion
76
Hominid Footprints
• Preserved in volcanic
ash at Laetoli, Tanzania
– Discovered in 1978 by
Mary Leakey,
– these footprints proved
hominids were bipedal
walkers at least 3.5
million years ago
– The footprints of two
adults and possibly those
of a child
– are clearly visible in this
photograph
77
Brain Size of A. afarensis
• A. afarensis had a brain size of 380–450 cubic
centimeters (cc),
– larger than the 300–400 cc of a chimpanzee
– but much smaller than that of present-day humans
(1350 cc average)
78
Ape-like Features
• The skull of A. afarensis retained many apelike
features,
–
–
–
–
including massive brow ridges
and a forward-jutting jaw,
but its teeth were intermediate
between those of apes and humans
• The heavily enameled molars
– were probably an adaptation to chewing fruits,
seeds, and roots
79
Landscape with A. afarensis
• Re-creation
of a
Pliocene
landscape
– showing
members
of
– Australopithecus
afarensis
– gathering
and eating
– various
fruits and
seeds
80
A. africanus Lived 3.0–2.3 mya
• A. afarensis was stratigraphically succeeded by
– Australopithecus africanus,
– who lived 3.0–2.3 million years ago
• The differences between the two species are
relatively minor
• They were both about the same size and
weight,
– but A. africanus had a flatter face
– and somewhat larger brain
81
Skull of A. africanus
• A reconstruction of
the skull
– of Australopithecus
africanus
• This skull,
– known as that of the
Taung Child,
• was discovered by
Raymond Dart in
South Africa in 1924
– and marks the
beginning of modern
paleoanthropology
82
Not As Well Adapted for
Bipedalism
• Furthermore, it appears the limbs
– of A. africanus may not have been
– as well adapted for bipedalism
– as those of A. afarensis
83
Robust Species
• Both A. afarensis and A. africanus differ
markedly from the so-called robust species
• A. boisei (2.6–1.0 million years ago)
• and A. robustus (2.0–1.2 million years ago)
• A. boisei was 1.2–1.4 m tall
– and weighed between 34 and 49 kg
• It had a powerful upper body,
– a distinctive bony crest on the top of its skull,
– a flat face, and the largest molars of any hominids
84
A. robustus Was a Vegetarian
• A. robustus, in contrast,
– was somewhat smaller (1.1–1.3 m tall)
– and lighter (32–40 kg)
• It had a flat face, and the crown of its skull
– had an elevated bony crest
– that provided additional area
– for the attachment of strong jaw muscles
• Its broad flat molars indicated
– A. robustus was a vegetarian
85
Australopithecus robustus Skull
• The skull of
Australopithecus
robustus
• This species had a
massive jaw,
– powerful chewing
muscles,
– and large broad
flat chewing teeth
– apparently used
for grinding up
coarse plant food
86
Separate Lineage
• Most scientists accept the idea
– that the robust australopithecines form a separate
lineage from the other australopithecines that
went extinct 1 million years ago
87
The Human Lineage
Homo habilis
• The earliest member of our own genus Homo
– is Homo habilis,
– who lived 2.5-1.6 million years ago
• Its remains were first found at Olduvai Gorge,
• Tanzania,
– but it is also known from Kenya, Ethiopia, and
South Africa
• H. habilis evolved from the A. afarensis and A.
africanus lineage and coexisted with A.
africanus for approximately 200,000 years
88
Stratigraphic Record
• The geologic age ranges
– for the commonly accepted species of hominids
89
Characteristics of Homo habilis
• H. habilis had a larger brain (700 cc average)
– than its australopithecine ancestors,
– but smaller teeth
• It was about 1.2-1.3 m tall and only weighed
32-37 kg
90
Homo habilis
• Homo habilis
• is the earliest
species of the
Homo lineage
• Shown is an
approximately
1.9 million year
old skull
– from Kenya
91
Transition from H. habilis to
H. erectus
• The evolutionary transition
– from H. habilis to Homo erectus
– appears to have occurred in a short period of time,
– between 1.8 and 1.6 million years ago
• New findings published in 2007 suggest
– that H. habilis and H. erectus apparently coexisted
– for approximately 500,000 years
92
Transition from H. habilis to
H. erectus
• Some scientists think that
– H. habilis and H. erectus may have evolved from
a common ancestor and represent separate
lineages of Homo,
– rather than the traditional linear view of H. erectus
evolving from H. habilis
93
Homo erectus
• In contrast to the australopithecines and H.
habilis, which are unknown outside Africa,
– Homo erectus was a widely distributed species,
– having migrated from Africa during the Pleistocene
• Specimens have been found
– not only in Africa
– but also in Europe, India, China (“Peking Man”),
– and Indonesia (“Java Man”)
94
Survived in Asia Until About
100,000 Years Ago
• H. erectus evolved in Africa 1.8 million years
ago
– and by 1 million years ago
– was present in southeastern and eastern Asia,
– where it survived until about 100,000 years ago
95
H. erectus Differed From Modern
Humans
• Although H. erectus developed regional
variations in form,
– the species differed from modern humans in several
ways
• Its brain size of 800-1300 cc,
– although much larger than that of H. habilis,
– was still less than the average for Homo sapiens
(1350 cc)
96
Size Similar to Humans
• The skull of H. erectus was thick-walled,
– its face was massive,
– it had prominent brow ridges,
– and its teeth were slightly larger than those of
present-day humans
• H. erectus was comparable in size to modern
humans,
– standing between 1.6 and 1.8 m tall
– and weighing between 53 and 63 kg
97
Skull of Homo erectus
• A reconstruction of
the skull of Homo
erectus
– a widely
distributed species
– whose remains
have been found
– in Africa, Europe,
India, China, and
Indonesia
98
H. erectus Was a Tool Maker
• The archaeological record indicates
– that H. erectus was a toolmaker
• Furthermore, some sites show evidence
– that its members used fire and lived in caves,
– an advantage for those living in more northernly
climates
99
Homo erectus Using Tools
• Recreation of a Pleistocene setting in Europe
– in which members of Homo erectus are
– using fire and stone tools
100
The “Out of Africa” View
• Debate still surrounds the transition from H.
erectus to our own species, Homo sapiens
– Paleoanthropologists are split into two camps
• On the one side are those who support
– the “out of Africa” view
• According to this camp, early modern humans
– evolved from a single woman in Africa,
– whose offspring then migrated from Africa,
• perhaps as recently as 100,000 years ago
– and populated Europe and Asia,
– driving the earlier hominid populations to extinction
101
The “Multiregional” View
• The alternative explanation, the “multiregional”
view
– maintains that early modern humans
– did not have an isolated origin in Africa,
– but rather established separate populations
throughout Eurasia
• Occasional contact and interbreeding
–
–
–
–
between these populations enabled our species
to maintain its overall cohesiveness,
while still preserving the regional differences
in people we see today
102
Homo sapiens Evolved
From H. erectus
• Regardless of which theory turns out to be
correct,
– our species, H. sapiens most certainly evolved from
H. erectus
103
Neanderthals
• Perhaps the most famous of all fossil humans are
the Neanderthals,
– who inhabited Europe and the Near East from about
200,000 to 30,000 years ago and according to the best
estimates,
– never exceeded 15,000 individuals in western Europe
• Some paleoanthropologists regard the
Neanderthals
– as a variety or subspecies of our own species (Homo
sapiens neanderthalensis),
– whereas others regard them as a separate species
(Homo neanderthalensis)
104
Specimens Found in Neander
Valley
• In any case, their name comes from the first
specimens found in 1856
– in the Neander Valley near Düsseldorf, Germany
105
Neanderthals
• The most notable difference between
Neanderthals and present-day humans is in the
skull
• Neanderthal skulls were long and low
– with heavy brow ridges, a projecting mouth,
– and a weak, receding chin
• Their brain was slightly larger on average
– than our own, and somewhat differently shaped
106
Neanderthal Skull
• The Neanderthals
were characterized
by prominent heavy
brow ridges, a
projecting mouth,
and a weak chin.
107
Cold Adapted
• The Neanderthal body was more massive and
heavily muscled than ours,
– with rather short lower limbs, much like those of
other cold-adapted people of today
• Neanderthal males averaged between 1.6-1.7 m
in height
– and about 83 kg in weight
108
Red Hair, Light Skin
• In 2007, scientists announced that they had isolated a
pigmentation gene from a segment of Neanderthal DNA
– that indicated that at least some Neanderthals had red hair and
light skin
• Furthermore, the gene is different from that of modern redhaired people,
– suggesting that perhaps Neanderthals and present-day humans
developed the trait independently,
– in response to similar higher northern latitude environmental
pressures
109
First Humans in Cold Climates
• Based on specimens from more than 100 sites,
– we now know Neanderthals were not much
different from us,
– only more robust
• Europe’s Neanderthals were the first humans
– to move into truly cold climates,
– enduring miserably long winters and short
summers
– as they pushed north into tundra country
110
Burial Ceremony in a Cave
• Archaeological evidence indicates
– Neanderthals lived in caves
– and participated in ritual burials
– as depicted in this painting of a burial ceremony
– such as occurred approximately 60,000 years ago
– at Shanidar Cave, Iraq
111
Took Care of Their Injured
• The remains of Neanderthals
– are found chiefly in caves and hut-like rock
shelters,
– which also contain a variety of specialized stone
tools and weapons
• Furthermore, archaeological evidence indicates
– that Neanderthals commonly took care of their
injured and buried their dead, frequently with such
grave items
– as tools, food, and perhaps even flowers
112
Cro-Magnons
• About 30,000 years ago,
– humans closely resembling modern Europeans
– moved into the region inhabited
– by the Neanderthals and completely replaced them
• Cro-Magnons, the name given to the
successors of the Neanderthals in France,
– lived from about 35,000 to 10,000 years ago
• During this period the development of art and
technology far exceeded anything the world
had seen before
113
Nomadic Hunters
• Cro-Magnons were skilled nomadic hunters,
– following the herds in their seasonal migrations
• They used a variety of specialized tools
– in their hunts, including perhaps the bow and arrow
• They sought refuge in caves and rock shelters
– and formed living groups of various sizes
114
Cro-Magnon Camp
• Pleistocene Cro-Magnon camp in Europe
115
Cave Painters
• Cro-Magnons were also cave painters
• Using paints made from manganese and iron
oxides,
–
–
–
–
Cro-Magnon people painted hundreds of scenes
on the ceilings and walls of caves
in France and Spain,
where many of them are still preserved today
116
Painting From a Cave in France
• Cro-Magnons were very skilled cave painters
– Painting of a horse
– from the cave of Niaux, France
117
Cultural Evolution
• With the appearance of Cro-Magnons,
– human evolution has become almost entirely
cultural rather than biological
• Humans have spread throughout the world
– by devising means to deal with a broad range of
environmental conditions
• Since the evolution of the Neanderthals
– approximately 200,000 years ago,
– humans have gone from a stone culture to a
technology that has allowed us
– to visit other planets with space probes
– and land astronauts on the Moon
118
Future
• It remains to be seen
–
–
–
–
how we will use this technology in the future
and whether we will continue as a species,
evolve into another species,
or become extinct as many groups before us have
done
119
Summary
• The primates evolved during the Paleocene
• Several trends help characterize primates
– and differentiate them from other mammalian
orders,
• including a change in overall skeletal structure and
mode of locomotion
• an increase in brain size
• stereoscopic vision
• and evolution of a grasping hand with opposable
thumb
120
Summary
• The primates are divided into two suborders
– the prosimians and the anthropoids
• The prosimians are the oldest primate lineage
– and include lemurs, lorises, tarsiers, and tree
shrews
• The anthropoids include
– the New and Old World monkeys,
– apes,
– and hominids, which are humans
• and their extinct ancestors
121
Summary
• The oldest known hominid is Sahelanthropus
tchadensis,
– dated at nearly 7 million years
– then two subspecies of Ardipithecus at 5.8 and 4.4 million
years respectively
• These early hominids were succeeded by the
australopithecines
– a fully bipedal group that evolved in Africa 4.2 million
years ago
• Recent discoveries indicate Ardipithecus evolved
into Australopithecus
122
Summary
• Currently, five australopithecine species are
known:
– Australopithecus anamensis, A. afarensis, A.
africanus, A. robustus and A. boisei
• The human lineage began
–
–
–
–
about 2.5 million years ago in Africa
with the evolution of Homo habilis,
which survived as a species
until about 1.6 million years ago
• Homo erectus evolved from H. habilis
– about 1.8 million years ago
– and was the first hominid to migrate out of Africa
123
Summary
• Between 1 and 1.8 million years ago, H. erectus
– had spread to Europe, India, China, and Indonesia
• The transition from H. erectus to H. sapiens is
still unresolved
– because there is presently insufficient evidence to
determine which hypothesis is correct
• the “out of Africa”
• or the “multiregional” hypothesis
• Nonetheless, H. erectus
– used fire,
– made tools,
– and lived in caves
124
Summary
• Neanderthals inhabited Europe and the Near East
– between 200,000 and 30,000 years ago
– and were not much different from present-day humans
• They were, however, more robust
– and had differently shaped skulls
• In addition, they made specialized tools and
weapons,
– apparently took care of their injured,
– and buried their dead
• The Cro-Magnons were the successors
– of the Neanderthals
– and lived from about 35,000-10,000 years ago
125
Summary
• Cro-Magnons were highly skilled nomadic
hunters,
– formed living groups of various sizes,
– and were also skilled cave painters
• Modern humans succeeded the Cro-Magnons
– about 10,000 years ago
– and have spread throughout the world
– as well as having set foot on the Moon
126
QUESTIONS?
127