Question

3. What evidence is there to suggest that the Earth is composed of tectonic plates?

Answer 1

From almost the creation of the first true maps of the Earth, people started seeing how continents would be able to fit together.  In particular, people noticed that South America fits almost exactly into Africa.

You should be aware that while world maps were around early in the 1600’s and better defined by the end of the 1700’s, those maps were not ‘public’ but were treated as state secrets.  And so it was not till much later that the broader ‘science’ community had access to good quality and accurate world maps.

It is now known that most of the major continental masses can be fit together in a jigsaw process.   In fact we now know that the continents were indeed once all joined together as one land mass – the super-continent of Pangaea.

If you look at most world maps you will ponder how this is evidence, as the continents really don’t appear to ‘fit’ together very well.  What you need to understand is that the vast majority of maps are drawn using a map projection that has the north and south poles (which are points) are a line the width of the map at the top and bottom.  This means that the map distorts the true shape of the Earth’s land and oceans as you love closer to the poles.    Some other map projections distort less, but have the map shape looking like segments of an orange.  See here for a range of map projections.  Check out the way Greenland changes size in each!

Answer 2

List of evidence:

1. The age and distribution of ocean sediments: the sediment in the ocean is thinner and younger than the age of the ocean indicates it should be  

2. The oceanic ridges: oceanic ridges are clear indicators of past events  

3. Terranes: oceanic plateaus that form by uplifting and mountain building as they strike a continent  

4. Paleomagnetism: strips of alternating magnetic polarity at spreading regions .

5. The location of the mountains and Fossils, resemble continents, like the ancient mountains ( although many have eroded to their cores ) and location of the rock types and fossils, all of it match up. With the fossil, tropical species found in the Antartic and similar fossils found in western Africa and Eastern South America.

6. Apparent polar wandering: plate movement caused the apparent position of the magnetic poles to have shifted  

7. Earthquakes and Volcanoes, if you check the map location of all the earthquakes recorded over time, almost all of them occur in plate boundaries. Hot spots: surface expression of plumes of magma . A volcanic island chain can form when a plate passes over a hot spot and a stationary mantle plume .

8. Atolls and Guyots: coral formations and submerged volcanic mountains. Guyots were once volcanic peaks above sea level