In the middle of the Cambrian, life on land was about to get a little more crowded. And those newcomers would end up changing the world. The arrival of plants on land would make the world colder, drain much of the oxygen out of the oceans and eventually, it would help cause a massive extinction event. For more videos like this, check out our Youtube channel: youtube.com/eons | Eons • PBS

We're entering the Earth's sixth era of extinction -- and it's the first time humans are to blame. Some ecologists are using microphones to record the sounds of one such disappearance. http://cnn.it/2iRqOkb | CNN