A mass extinction                   . a. is global in scale; b. affects many different groups of organisms; c. is caused only by human activity; d. A and B are correct; e. A, B, and C are correct

Video transcript

Welcome back. Here's our next problem. We are in the midst of the sixth mass extinction which is primarily caused by human activity and is also known as the and our choices are cretaceous tertiary extinction, devonian extinction, holocene extinction, Triassic Jurassic extinction. And let's recall what a mass extinction is and that would be a widespread decrease in earth's biodiversity. So massive die off of different species Of living things at one time. So let's look at our different periods here. Well, we can recall that the cretaceous period, devonian period, Triassic and Jurassic periods. These are all far far in the past. The Holocene period is what we are currently living in. So a mass extinction occurring currently would be the holocene extinction which is choice. See that were given here. But let's just walk through the other choices were given Choice a says cretaceous tertiary extinction. Well this is kind of the famous one um this is about 66 million years ago and this is the end of the dinosaurs and we see the evidence of this layer of sediment um widespread through the out the earth that led to the belief um that it was probably caused by an asteroid impact. So that's kind of the one that everybody knows about there. Choice B. O. So we'll say we're going to go ahead and cross out choice A that's not currently what we're living through Choice B is the devonian extinction. So that's even longer ago, the Devonian period very early on. Just as the continents are starting to come together in Pangaea before they split apart. So this is about 370 million years ago and this mostly affected marine species and it is thought to have occurred due to oxygen deprivation and low temperatures. And so it's thought that perhaps that was an asteroid as well, We don't really know. That's a very long time ago. So that's sort of speculation based on fossil records but obviously not what we're living through right now. Cross out Choice B and finally Choice D the Triassic Jurassic extinction. Um and that's about 200 million years ago during the time of the dinosaurs. And this is what it caused many reptile species to die off. That's what led to um dinosaurs and pterosaurs dominating the land area as other reptile species died off and lead to the end of a group of animals you like animals called confidants completely eliminated in the fossil record at once. So those are some past mass extinction events. Choice D. Obviously that we're currently living through either across that out. But our current period is the Holocene period. So the current uh sixth mass extinction were believed to be living to through mainly due to human activity would be called choice. See the holocene extinction. See you in the next video