Asked by: Gemma Jones, Nuneaton

The Earth's axis is tilted at around 23 degrees to its orbit, and has more or less stayed like that for tens of thousands of years. But in the 1990s, astronomers discovered that because of the way the gravity of the planets interact, it can cause dramatic changes in axial tilt.

It was believed that the Earth is protected from similarly dramatic changes by the presence of the Moon, whose relatively strong gravitational influence ensures our planet stays more or less upright. But this comforting view has recently been challenged by studies of ancient sediments found in a remote Norwegian archipelago. By studying the magnetic properties of 800 million-year-old samples, American scientists found evidence that the Earth may have tilted over by more than 50 degrees in the distant past. There is a 140-year-old theory which predicts that Earth tilts in response to changes in the distribution of weight on its surface, such as the shifting continents.

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Robert is a science writer and visiting professor of science at Aston University.