The mysterious phenomenon, dubbed the "100-thousand-year problem," has been repeated over the past million years and has led to the icing of North America, Europe and Asia. Until the last moment, scientists could not explain why this is happening.
Previously, ice ages on our planet occurred at intervals of 40 thousand years. However, almost a million years ago, during the Middle Pleistocene transition, the intervals between ice ages lengthened from 40 thousand to 100 thousand years.
A new study from Cardiff University in the UK suggests that the oceans are to blame for this change, namely the way they "suck" carbon dioxide from the atmosphere.
By studying the chemical composition of the tiny fossils on the ocean floor, the team found that more CO2 was entering the ocean depths during ice ages that lasted 100,000 years. This means that extra carbon dioxide was being pulled out of the atmosphere and into the oceans, lowering the temperature on Earth, causing huge ice sheets to cover the Northern Hemisphere.
Algae play a key role in removing CO2 from the atmosphere, as carbon dioxide is the most important ingredient in photosynthesis. CO2 is released back into the atmosphere when water from the deep ocean rises to the surface in a process called upwelling. But when the volume of sea ice is huge, less CO2 is released into the atmosphere, which increases the ice cover and prolongs the ice age.
The Earth is now going through a warm period. The last ice age ended 11 thousand years ago. Since then, temperatures and sea levels have risen, and the ice caps have retreated back towards the poles. The planet's warming is also accelerating man-made carbon dioxide emissions.