re: learning
There has been a regular cycle of ice ages and warming periods for hundreds of thousands of years. Over longer periods, there have been major events like asteroid collisions and gigantic volcanic eruptions.
A little perspective:
The 100,000 year range is a blip on the end at the right. Note also that the current ppm rating for CO2 is around 380.
Obviously, life for individual species was anything but stable--there were four mass extinctions during the Cambrian period alone--but the Earth, and complex ecosystem, have survived.