Download of the same age is form in southern Africa, South America, India, and

3.4.2 - Continental Puzzle
http://www.imaginiquebengals.com/condriplatec.pdf
Background: The activity you just completed showed you that the continents actually fit
together like puzzle pieces. But that isn’t even close to all of the evidence that is hidden
within the continents that scientists began to recognize in the early-mid 1900s. Let’s
look through some of those.
Fit of the continents: In the 1960s, it was recognized that, especially if you take the
continental slope into account, the continents fit together incredibly well. Just look at
South America and Africa to the right.
Fossil Evidence across continents: Alfred Wegener could not propose an idea like
plate tectonics without having more evidence than simply continent shape. To help his cause, Wegener also
discovered that there were fossils located directly opposite each other on widely separated continents. For example,
referencing the South America and Africa picture to the left, the fossils of Mesosaurus can be found on both sides of
the Atlantic Ocean. South Carolina actually has evidence of this, as the
upstate has a band of trilobite fossils that are not natural to North
America, but instead reigned on African soil. This indicates that parts of
South Carolinian crust actually originated as African continental crust.
Similarly, marsupial (kangaroos, wallabies, koala, possums, opossums,
wombats, etc.) fossils are found in Australia, Antarctica, South America,
and North America. If you look at the image to the right below, this is
Earth 80 million years ago when marsupial mammals first appeared.
Notice that Australia, Antarctica, and South America are all connected at
this point, allowing marsupials to populate all three continents before they
separated. We also continue to find fossils throughout the world of plants or animals that could not have existed in
that environment (tropical plants in Antarctica, sea
fossils in the middle of the desert, etc…)
Rock Type and Structural Similarities:
We find similar rock types on continents on opposite
sides of the Atlantic Ocean. These rocks in both the
Appalachian Mountains, the British Isles, and Caledonian Mountains all have similar age, composition, and structure.
Comparing the image below on the left, to the image on the right, if North America, Europe, and Africa are
reassembled, these mountain ranges form a continuous mountain range.
Paleoclimatic Evidence:
Glacial till (unsorted sedimentary rock deposited by glacier movement) of the
same age is form in southern Africa, South America, India, and Australia. This
would be nearly impossible to explain currently without the knowledge that at
one point nearly 200 million years ago, the supercontinent Pangae existed,
which placed these 5 current day continents next to each other. The image to
the right should give you an idea of their placement, and should give a prelude
to Australia, Antarctica, and South America being connected in the marsupial
migration issue referenced in the fossil section.
Paleomagnetism:
We saw during the Mid-Atlantic Ridge seafloor spreading lab, that when
igneous rock is created, any magnetic minerals in that rock crystalize and align
themselves within the Earth’s current magnetic field. This is important because if the continents had not moved,
igneous rocks on every continent should point towards the current magnetic North Pole. However, this is not the
case. When you compare current day North America and Europe, they are not pointing in the same direction. If you
compare the two images below, you will notice
as you rotate North America counter-clock wise
as you move from Figure A to Figure B, the
green and red lines that represent magnetic
orientation begin to line up.
The latitude that the rock is created at also
influences magnetic orientation of igneous rock.
As you can see in the image below, because of
the magnetic waves surrounding the Earth, the
magnetic crystals formed would orient
themselves similar to the dip needles in the
image and make latitude easy to figure out.
Pangea:
The above evidence all points towards all of the land on Earth
being combined into a supercontinent called Pangaea that formed
about 270 million years ago and started to break up about 200
million years ago. It was not the first supercontinent (there have
been at least 6 proposed supercontinents and upwards up 15
previously) and it will likely not be the last. The Americas are
separating from Africa, The Americas are traveling towards
Eurasia, Oceania (including India) are driving north, and Africa is
still pushing into Eurasia.
Check out this website real quick for an animation of the entire
process of Pangea beaking up: http://geologyguy.com/teaching/iac/animations/pangaea.htm
Review Questions
1. List, and briefly explain, the 5 major pieces of evidence listed above
that exist that indicate that Earth’s plates are moving and were once combined into .
2. When did Pangaea form and when did it break up?
3. Was Pangaea the only supercontinent that has existed? If not, how many have existed in the past?
4. For the animation linked above, how long ago (in millions of years) did the animation start?
5. How frequently(every how many millions of years) did it pause for a moment?