Many mountains in Indonesia and neighboring Papua New Guinea consist of ancient volcanic rocks from the ocean floor that were caught in a colossal tectonic collision between a chain of island volcanoes and a continent, and thrust high. Lashed by tropical rains, these rocks hungrily react with CO2 and sequester it in minerals. That is why, with only 2% of the world’s land area, Indonesia accounts for 10% of its long-term CO2 absorption. Its mountains could explain why ice sheets have persisted, waxing and waning, for several million years (although they are now threatened by global warming).

Now, researchers have extended that theory, finding that such tropical mountain-building collisions coincide with nearly all of the half-dozen or so significant glacial periods in the past 500 million years.

Rise of carbon dioxide–absorbing mountains in tropics may set thermostat for global climate