There is variety of evidence that supports the claims that plate tectonics accounts for (1) the distribution of fossils on different continents, (2) the occurrence of earthquakes, and (3) continental and ocean floor features including mountains, volcanoes, faults, and trenches.
1. The Distribution of Fossils on Different Continents
Many fossil comparisons along the edges of continents that look like they fit together suggest species similarities that would only make sense if the two continents were joined at some point in the past. For example the fern-like plant called Glossopteris, which flourished almost 300 million years ago, is found in Antarctica, Australia and India as well as Africa and South America. This indicates that Glossopteris lived at a time when all of these continents were joined in a single supercontinent, which geologists refer to as Pangaea.
|
2. The Occurrence of Earthquakes
The location of earthquakes and volcanoes are not random. There is a large amount of seismic, volcanic activity along the plate boundaries. This is shown clearly below where the earthquakes above magnitude 5.0 are plotted for a 10-year period. The concentration is striking, and this plot also serves to define the plate boundaries extremely well.
- Here is a clickable map of current earthquake activity on Earth.
3. Geologic Features Found on the Continents and Ocean Floor
Most continental and oceanic floor landforms are the direct result of geological activities that occur along plate boundaries. The landforms observed at these locations depends on whether the plates are being pushed together (converging) to create mountains or deep ocean trenches, being pulled apart (diverging) to form new ocean floor at mid-ocean ridges, or sliding past each other (transform) creating faults.
There are ridges, such as the Mid-Atlantic Ridge where plates are separating that are produced by lava welling up from between the plates as they pull apart. Likewise, there are mountain ranges being formed where plates are pushing against each other such as the Himalayas, which are still growing. The following diagram demonstrates some of the most common landforms found along different plate boundaries.
There are ridges, such as the Mid-Atlantic Ridge where plates are separating that are produced by lava welling up from between the plates as they pull apart. Likewise, there are mountain ranges being formed where plates are pushing against each other such as the Himalayas, which are still growing. The following diagram demonstrates some of the most common landforms found along different plate boundaries.
4. Additional Evidence
GPS Evidence - The movements of these plates can be measured using GPS. GPS uses a system of satellites to triangulate the position of a receiver anywhere on Earth. Scientists can very accurately determine how the plates behave.
Climate and Glacial Evidence - There is also much climate evidence supporting plate tectonics, most notable of which is glacial activity. Alfred Wegener investigated this and found glacial deposits that once covered all the southern major plates. If the continents were in their current positions about 300 million years ago, this glacier would cover most of the globe and extend above the equator. Also, glacial striations (essentially ‘cut marks’) found in rocks from the movement of this ice sheet show that the direction in which it was moving was outwards from a central point in southern Africa. If the continents were next to one another at the south pole, these striations line up with each other.
|
Age of the Sea Floor - If the crustal plates are pulling apart at boundaries like the Mid-Atlantic Ridge, the seafloor near these ridges should be very young geologically, since it is formed of material recently coming from from the interior. This is indeed the case, as the following figure shows.
Video Guide:
|
|
Topic Tips
- There is a lot of evidence in favor of the theory of plate tectonics including, (1) the distribution of fossils on different continents, (2) the occurrence of earthquakes, and (3) continental and ocean floor features including mountains, volcanoes, faults, and trenches. Plus, a whole lot more!