On another EarthDate, we talked about Greenhouse and Icehouse periods in Earth’s history that last hundreds of millions of years. In Greenhouse times, temperatures rise and life flourishes. And in Icehouse periods, temperatures fall and life can struggle.

Why does Earth alternate between these extremes? Research points to plate tectonics and volcanic activity.

Plate movement causes continents to be pulled apart and pushed together, with varying amounts of volcanic activity.

When there’s lots of activity, volcanoes emit huge volumes of CO2 and methane into the atmosphere, which can trap enough heat to bring about a Greenhouse period.

Conversely, when volcanic activity decreases, CO2 and methane decrease, and the Earth can cool.

Continental movement also affects ocean circulation. If Earth’s poles become isolated from the warm waters near the equator, they can freeze more easily.

And plate movement can bury large volumes of organic carbon in sediment layers, stopping it from reentering the atmosphere.

Within Icehouse periods, there are shorter glacial cycles, interrupted by milder interglacials, like the one we’re in today. Earth alternates between more ice and less ice mostly because of changes in its orbital path.

When Earth’s orbit stretches farther from the sun, Earth cools and continental glaciers form. When it moves back closer to the sun, the ice melts.

Understanding the causes of these long-term and short-term climate cycles helps us to better understand the complexities of Earth’s climate today.