Continental Drift and Major Extinctions

1. Plate Tectonics

Continents are actually only the surfaces of larger plates called tectonic plates, most of which are underwater. Tectonic plates cover the entire Earth's surface. These tectonic plates float on Earth's molten inner layer called the mantle.

The plates are in constant motion. They are colliding, sinking, crawling over each other, and pulling apart from one another entirely.

• When two plates pull away, the gap can fill with molten lava from the mantle, which forms either a volcano or a trench.
• When two plates that have similar densities collide, they push upon each other and form mountains.
• When two plates with different densities collide, one will slide underneath the other. and that section will melt back into molten lava, shrinking the plate's overall size.
• When two plates rub against each other as they pass, it creates what we know as an earthquake.

2. Continental Drift

Throughout history, these plates and the continents have been moving and shifting all over Earth. Between 225 and 275 million years ago, all of the continents were combined into what is called Pangaea, a supercontinent, shown below. See how South America actually kind of fits into Africa like a puzzle?

As continental drift continued, this supercontinent was separated. The species were separated from each other, eventually evolving into their own groups over time, resulting in greater planetary biodiversity. The more separated the continents are, the more shoreline area there is, and the more overall biodiversity we have. Today, the continents are more widely spread.

This model of tectonic plates and continental drift wasn't actually scientifically accepted until oceanic scientists in the 1960s discovered that the seafloor does, in fact, spread. Other pieces of evidence that support the theory of continental drift and plate tectonics are identical fossils on separate continents, areas where continents were believed to have been connected previously, and identical plant and animal groups in locations where continents are believed to have been connected.

Continental drift and plate tectonics are a scientific theory. While widely accepted, they are not a proven fact. Future science may discover better explanations for the way the continents were formed or how they move.

3. Major Mass Extinctions

Earth's history has not had a steady linear increase in biodiversity. There have been fluctuations, biodiversity expansions, and mass extinctions. There are five major known mass extinction periods on Earth, with many smaller ones as well (see diagram below). We're going to discuss the five major ones. We have been able to identify these periods of extinction by studying fossil records.