We See It in the Fossil Record
Many reports on climate change and extinction focus on the last hundred years or so. But it could be that we're in the middle of an extinction that started about 40,000 years ago, as humans started to settle new areas of the planet. This includes the period a lot of people think of as the last big extinction: the end of the last ice age, when animals like the woolly mammoth and saber-tooth cat became extinct.
It's easy to think of the ice age as its own, isolated event. But people who study the fossil record follow a much longer timeline — one of millions of years instead of thousands. It can take about 100,000 years for a mass extinction to play out in the fossil record. In other words, future scientists may look back on the fossil record and see a pattern that begins tens of thousands of years ago and extends through today. We can see some of this in the fossil record already, and in more recent archaeological evidence.