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Bombardments of 'micro-meteorites' on Earth and Mars four billion years ago may have caused the planets' climates to cool dramatically, hampering their ability to support life, according to research by Imperial scientists published on 1 April in the journal Geochimica et Cosmochimica Acta.

Micro-meteorites, the size of sugar grains, come from the rocky asteroid belt between Mars and Jupiter, and are dragged by gravity towards Earth and Mars. As they enter the planets' upper atmospheres, they heat up to temperatures of approximately 1,000 degrees Celsius and release gases, including sulphur dioxide. This sulphur dioxide forms aerosols consisting of solid and liquid particles, which deflect sunlight away from the surface, making the planets cooler.

The researchers studied the effects of the Late Heavy Bombardment, a period of time in the early solar system, when meteorite showers lasting around 100 million years barraged Earth and Mars.

They believe that the high sulphur dioxide levels, together with a Sun 30 per cent weaker than today's, could have plunged Earth into an Arctic winter lasting millions of years, and making conditions for primitive microbial life extremely difficult.

Dr Richard Court (Earth Science and Engineering), lead author of the study, said: "These sugar grain sized meteorites are left over material from the construction of our early solar system, helping to build rocky planets such as Earth and Mars. Our study is helping us to see how these tiny space rocks could also bring environmental devastation on a global scale to early Earth and Mars.