NOVA

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Caitlin

Despite being above the Arctic Circle, Lake El'gygytgyn has never been covered by glaciers, which means that when sediment, all that material floating or living in the water, settled on the bottom of the lake it formed layers that have remained undisturbed. So you start to accumulate sediments at the bottom of the lake, but also what's accumulating in there is organic matter. So, anything that's living on the landscape can get washed into the lake. So, all of those elements give us a snapshot of what the ecosystem was like, and that ecosystem then can tell us something about the climate at the time. What pollen counts from the past million years show us is that the climate around Lake El'gygytgyn has been oscillating, or changing, from warmer periods to colder periods. Each period lasting thousands of years. It's like a detective story doing this work. And just like solving a mystery, it's best when you have multiple lines of evidence all pointing to the same conclusion. We can actually take pollen counts and combine it with data from diatoms and those mammoth poop-eating fungal spores to understand how this lake has changed over the last million years. And we can combine the lake data with similar cores from around the world. All of those elements give us a snapshot of what the climate was like. -

Caitlin

For the last 34 million years, Earth has actually been an icehouse, with ice at at least one of the poles year-round. And here's the big lesson that El'gygytgyn has taught us. That even within an icehouse, the temperature oscillates between very cold periods, called glacials when ice sheets extend down over the continents, and warmer inter-glacial periods, like today when there is still ice, but it's confined to the poles. The big question is why. It turns out that what drives glaciation, for the most, are three changes in Earth's orbit around the Sun. The orbit can be more oval or more circular, the tilt of the planet can increase or decrease, and Earth's axis wobbles like a top. These changes occur over tens to hundreds of thousands of years and they affect how heat from the Sun warms different parts of the planet. But that's only part of the story because the orbital cycles and the position of the Earth can't explain why the changes in temperature are so extreme and why they're global. So, what else is going on here? You're about to find out. (gentle music)