Transcript: In addition to gradual change over billions of years, Earth’s climates has been fluctuating and subject to instabilities that have taken it to extremes that are hard for us to imagine. In a period of six hundred to seven hundred and fifty million years ago, Earth was subject to a series of deep ice ages when glaciers reached nearly to the equator, and the oceans froze to a depth of about a kilometer. This is hard for us to imagine. It got this way because a normal fluctuation made the Earth cooler at which point the glaciers advanced, and the oceans began to freeze. Ice reflects ninety percent of light incoming rather than five percent for water. As the oceans reflect more light, they get colder still accelerating the freezing process in a runaway fashion. However, during this time volcanic activity, driven by energy sources deep in the Earth, does not diminish, and so eventually carbon dioxide is released which is not absorbed in the oceans because they are frozen. So it builds up in the atmosphere, warming the planet and melting the ice, and more sunlight gets absorbed. This also becomes a runaway process, and the large amount of carbon dioxide leads to an overshoot, an enormous warming of the temperatures. Thus, there are instabilities in the Earth’s atmosphere that can lead to climate extremes which must have affected life on Earth at the time.