New evidence for an unexpected player in Earth’s multimillion-year climate cycles: the planet Mars

By Adriana Dutkiewicz, University of Sydney, Dietmar Müller, University of Sydney, Slah Boulila, Sorbonne Université

Our existence is governed by natural cycles, from the daily rhythms of sleeping and eating, to longer patterns such as the turn of the seasons and the quadrennial round of leap years.

After looking at seabed sediment stretching back 65 million years, we have found a previously undetected cycle to add to the list: an ebb and flow in deep sea currents, tied to a 2.4-million-year swell of global warming and cooling driven by a gravitational tug of war between Earth and Mars. Our research is published in Nature Communications.

Milankovitch cycles and ice ages

Most of the natural cycles we know are determined one way or another by Earth’s movement around the Sun.

As the German astronomer Johannes Kepler first realised four centuries ago, the orbits of Earth and the other planets are not quite circular, but rather slightly squashed ellipses. And over time, the gravitational jostling of the planets changes the shape of these orbits in a predictable pattern.

These alterations affect our long-term climate, influencing the coming and going of ice ages. In 1941, Serbian astrophysicist Milutin Milankovitch recognised that changes in the shape of Earth’s orbit, the tilt of its axis, and the wobbling of its poles all affect the amount of sunlight we receive.

Known as “Milankovitch cycles”, these patterns occur with periods of 405,000, 100,000, 41,000 and 23,000 years. Geologists have found traces of them throughout Earth’s deep past, even in 2.5-billion-year old rocks.

Earth and Mars

There are also slower rhythms, called astronomical “grand cycles”, which cause fluctuations over millions of years. One such cycle, related to the slow rotation of the orbits of Earth and Mars, recurs every 2.4 million years.

The cycle is predicted by astronomical models, but is rarely detected in geological records. The easiest way to find it would be in sediment samples that continuously cover a period of many millions of years, but these are rare.

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