Hi, I'm Jensen Morgan. We're going to talk about some great concepts in environmental science. Today's topic is continental drift and major extinctions. So let's get started.
We're going to talk about plate tectonics, continental drift, and major extinctions. Continents are actually only the surface of a larger plate called the tectonic plate, most of which is under water. Tectonic plates cover the entire Earth's surface. These tectonic plates float on the Earth's molten inner layer called the mantle.
The plates are in constant motion, colliding, sinking, and 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 they collide and the plates have a similar density, they push upon each other and form mountains.
When they collide but their densities are different, 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.
Throughout history, these plates and the continents have been moving and shifting all over the Earth. Between 225 and 275 million years ago, all of the continents were actually combined in what is called Pangaea, a super continent, which looks something like this. See how South America actually kind of fits into Africa like a puzzle?
As continental drift continued, this super continent 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, which is better for biodiversity overall. 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 and areas where continents were believed to have been connected previously, 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 proven fact. Future science may discover better explanations for the way the continents were formed or move.
Earth's history has not been a steady linear increase in biodiversity. There have been fluctuations, biodiversity expansion, and mass extinction. There are five major known mass extinction periods on earth with many smaller ones as well. We're going to discuss the five major ones. We have been able to identify these periods of extinction through studying fossil records.
The first was about 439 million years ago. It was caused by glacial melting and killed approximately 60% of life forms, all of which were marine because the vast majority of life at that point was aquatic. The second was about 364 million years ago and is called the Late Devonian extinction. It killed approximately 57% of life on Earth and was likely the result of an asteroid impacting the planet.
About 251 million years ago, approximately 96% of marine life and 70% of terrestrial life was wiped out by what is thought to have been a volcanic eruption, asteroid impact, or supernova. This is called the Permian-Triassic extinction. Some scientists speculate that it was caused by Pangaea and the subsequent loss of biodiversity, because it occurred over a few million years and biodiversity levels did not return to full strength until six million years after the extinction ended.
The fourth, the end-Triassic extinction is thought to have been massive flooding or lava eruption from the central Atlantic ocean between about 199 to 214 million years ago. It wiped out 50% of marine life. The fifth and final known major extinction is the Cretaceous-Tertiary extinction, which is thought to have happened 65 million years ago by some sudden cataclysmic event.
The leading theory suggests that an asteroid struck somewhere in the Gulf of Mexico region, which set off a set of volcanic eruptions, fires, tidal waves, and severe storms. The combined result was an elimination of sunlight, which both plants and animals require for survival. It ended the 165 million-year era of the dinosaurs. And humans evolved just after about 64 million years ago.
Now, let's have a recap. We talked about plate tectonics, continental drift, and major mass extinctions. Well, that's all for this tutorial. I look forward to next time. Bye.