Now, things haven't always been great for life on Earth. In fact, there have been about 5 mass extinctions, which are periods where the majority of lineages, meaning the majority of different species out there, actually die out in a very short period of time. Basically, like, less than 1,000,000 years, which doesn't sound like a lot. But when you consider that life has been around on Earth for 1,000,000,000 years, well, now it puts it in perspective. Right? So the majority of lineages die out in a short period of time, and this results in a dramatic reshaping of life on the planet. And, of course, one of the most famous mass extinctions, as pictured right here by this totally freaked out T Rex, was the extinction of the dinosaurs, thought to have occurred due to an asteroid impact.

Now this table right here shows you some of the other mass extinctions. So here, we have the end of the dinosaurs, and let me actually change my colors, so it's easier to see. Here's another mass extinction. Here's another one known as the great dying, and there are actually two earlier ones, that are also considered mass extinctions. But we don't really need to worry about specific mass extinctions. Just know that they have occurred throughout Earth's history, and essentially, it's a one door closes, another door opens situation. Because so many of the species out there die off, it gives a great opportunity to the remaining species to fill a lot of the niches left behind by those species, and it allows life to completely reshape the environment.

So when that happens, we often have something called an adaptive radiation, which is the process by which organisms rapidly diversify into many new forms, often in response to changes in the environment that shift evolutionary pressures and open niches. So on a grand scale, when we have mass extinctions, we frequently have adaptive radiations following that, but on a very grand scale. However, adaptive radiations can also happen on a much smaller scale.

And a wonderful example of this is in the Galápagos finches. And, yes, this is the same example that Darwin took note of, which led him to developing his theory of descent with modification. So the Galápagos Islands present many different environments, and the finches on each of these islands have evolved to unique forms. So they all started from a common ancestor finch pictured here, this little guy. And depending on the environment, the finches found themselves in, they experienced different evolutionary pressures and evolved to fill different niches, as evidenced by all these finches on the outside of the circle.