Please answer the questions in attachment.
Geol 1202 Planet Earth
Assignment – Reconstructing the Atlantic
The Atlantic Ocean, the second largest ocean on Earth, covers about 19% of
the planet. The North Atlantic, which separates North America and Europe,
began to form about 180 Ma when the supercontinent Pangaea broke apart.
The South Atlantic which was a bit later opening, about 130 million years
ago, separates the continents of South America and Africa.
New ocean crust is produced at the mid-Atlantic ridge, a line of volcanoes
and mountains in the center of the ocean. This ridge is the longest mountain
chain in the world, 11,300 km, and has peaks rising 4 km above the ocean
floor. Iceland represents one of the locations where the ridge rises above the
ocean.
The Atlantic has reached a width greater than 9600 km and continues to
grow.
In this exercise, you will reconstruct the positions of the continents during the
opening of the Atlantic Ocean, over a period of about 200 million years. The
data on which this exercise is based come from magnetic anomalies in the
Atlantic Ocean, which have been identified and correlated to produce a map
showing the age of the ocean floor. In fact, calculating plate movements is
quite a complex task because the Earth’s surface is curved.
For this exercise, you will use a map that has been slightly adapted so that you can simulate the plate
movements on a flat surface.
Be sure to read the instructions all the way through before you begin.
Instructions:
Part 1: Print, measure, cut and paste
Print the map figure on the last page – it is in colour but the colours are different enough that they will be
distinguishable if you print it in grey scale. You may still have to refer back to the colour version to make
sure you are cutting along the correct boundary though.
You may want to print several copies. You will be required to scan or photograph your reconstruction at
each stage and you may find it better to keep a copy.
Stage 1: Present Day
On the map, notice the positions of Halifax (H), St. John’s (S), Labrador City (L), Casablanca (C), Madrid
(M) and Edinburgh (E), marked by the red dots. Using the scale from the map, measure the distance from
Halifax to Casablanca. Then, in the same manner, measure the distance from St. John’s to Madrid and the
distance from Labrador City to Edinburgh. (You may have to do a bit of calculation to figure out the
distances from the scale; this will depend on the size of your print-out – ask me if you cannot figure out
how to use the scale.)
I have already done the present day distances for you. But you should go through the process and make
sure your distances are close to mine. This will let you know if you are doing it right.
Record these distances in the table provided.
Stage 1: 40 Ma
Carefully cut out the ocean floor that is younger than 40 Ma (million years) – the red and orange band in
the center. Also, there is some ocean floor that is white (unknown age) between Canada and Greenland,
and between Greenland and Europe. You can remove this too: it gets in the way! You should also make a
cut separating the European Plate from the African Plate, and a cut between North and South America
(the dashed lines). So you should now have four pieces of paper altogether – these represent tectonic
plates. Slide the plates together to make a best fit between them, to show their positions at the end of
Eocene time, and secure them loosely with tape.
Photograph your reconstruction at this stage.
Measure the three distances between the cities again and record them in the table.
Stage 2: 84 Ma
Repeat the exercise, but this time remove the ocean floor back to the end of the Middle Cretaceous
Period, 84 million years ago (i.e. remove the yellow and green bands). You will find you have to cut off
Iberia (Spain and Portugal) as a separate plate from the rest of Europe to make this work. (You can print
additional copies of the map if you wish to keep the previous reconstruction while you work on the
Cretaceous one.) Tape the plates together; you should find the Atlantic Ocean is much narrower!
Photograph your reconstruction at this stage.
Then measure and record the three distances again.
Stage 3: 180 Ma
Finally, remove all the ocean floor! This will include the two blue bands and the older crust represented by
the pink and purple as well. Remember to leave the pale blue continental margins attached to the
continents because they are underlain by continental crust.
Secure the continents together in their positions before the opening began 180 million years ago. This will
show the arrangements of the continents in the Jurassic Period. You may find there are some places
where the boundaries do not match exactly: this is to be expected because the continental margins
actually stretch during rifting. Put your continents into your best estimate of their arrangement before the
Atlantic Ocean started to open. At this point, all the continents now found around the North Atlantic were
part of a single large continent (or ‘supercontinent’) called Pangaea.
(Hint: South America will need to rotate quite bit to fit)
Photograph your reconstruction at this stage.
Measure the three distances on this reconstruction and record them in the table.
Remember: your distances should be in kilometers (and make sense) Given the sale of the map figure
about the best you will be able to measure will be to the nearest 50km.
TIME (Ma)
0 Ma
40 Ma
84 Ma
180 Ma
RATE (cm/year)
Labrador City to Edinburgh
4400km
DISTANCES
St. John’s to Madrid
3300km
Halifax to Casablanca
3900km
Part 2: Rate of Plate Movement
In this part of the assignment you are going to use the distances you recorded in Part 1 to
calculate the rate at which the Atlantic Ocean was opening. This involves a very simple calculation.
The equation is: Rate = Distance/Time
In our case:
Rate is the rate at which the Atlantic Ocean opened.
Distance is those numbers that you found in Part 1. You will have to subtract the last distance you found
for each set of cities (which represents the distance before the opening of the ocean) from the Present Day
distance. This will give you the distance the plates moved during that period.
Time is represented by the ocean floor that you removed in Part 1.
You should end up with a rate of movement for each set of cities (three in total) – your initial value will be in
km/ millions of years.
You need to convert this to cm/year.
I will make this part easy for you:
Conversion Formula:
km/Ma x 1000m/km x 100cm/m x Ma/1,000,000 = cm/year
or
convert kilometres to centimetres – 100,000cm/km
convert Ma to years – 1,000,000 years/Ma
Enter these rates in your table.
What to submit?
You should submit a photograph of your reconstruction at each stage – if there is no photos I will reduce
your final grade on the assignment by 50%.
Submit a photograph of your completed table.
Submit the answers to these questions.
Based upon your calculations what is …
1. the rate of widening of the Atlantic between St. John’s to Madrid?
2. the rate of widening of the Atlantic between Halifax and Casablanca?
3. the rate of widening of the Atlantic between Labrador to Edinburgh?
Note: make sure you include your calculations. If you have the wrong answer but I can see where you
went wrong I can give part marks.
continental
crust
shelf
180-147
147-132
132-84
84-68
68-47
47-40
40-10
10-0
(millions of years)
age of the
ocean floor
km
North
America
N
0
South
America
L
1000
H
S
E
C
M
Africa
Europe