Massive bombardments of meteorites from space may have turned Earth into a haven for life, scientists said today. And the same could have happened on Mars.
As each meteor entered the atmosphere, extreme heat caused minerals and organic material on its outer crust to be released. These formed water that fell as rain plus the greenhouse gas carbon dioxide which trapped energy from sunlight.
The heavy bombardment lasted around 20 million years. The result was that Earth and Mars became warm and wet enough to form and keep vast liquid oceans – though the water on Mars has long evaporated into space or sunk underground.
Researchers at Imperial College London analysed the remains of 15 fragments of ancient meteorites that had crashed around the world. They then baked them at very high temperatures just like they would experience when entering the atmosphere to see how much material they released.
They found that on average, each meteorite was capable of releasing up to 12 per cent of its mass as water vapour and 6 per cent of its mass as carbon dioxide. This is too small for an individual meteor to have an effect.
However, records show that an ancient meteorite shower called the Late Heavy Bombardment occurred four billions years ago where millions of rocks crashed to Earth and Msrs over a 20-million-year period.
The researchers calculate that this would have dumped 10 billion tonnes of carbon dioxide and 10 billion tonnes of water vapour into each planet’s atmosphere every year.
Professor Mark Sephton, from Imperial’s Department of Earth Science and Engineering believes the study provides important clues about Earth’s ancient past. He said yesterday: “For a long time, scientists have been trying to understand why Earth is so water rich compared to other planets in our solar system.
“The Late Heavy Bombardment may provide a clue. This may have been a pivotal moment in our early history where Earth’s gaseous envelope finally had enough of the right ingredients to nurture life on our planet.”
Colleague Dr Richard Court added: “Because of their chemistry, ancient meteorites have been suggested as a way of furnishing the early Earth with its liquid water. Now we have data that reveals just how much water and carbon dioxide was directly injected into the atmosphere by meteorites. These gases could have got to work immediately, boosting the water cycle and warming the planet.”
The research is published in the journal Geochimica et Cosmochima Acta. Imperial College scientists previously found ingredients for life in meteorites lying in the Antarctic.
But why has Mars lost its oceans? Unlike Earth, Mars lacks a magnetic field to act as a protective shield from the Sun’s solar wind. As a consequence, Mars was stripped of most of its atmosphere and water evaporated into space or formed ice underground around the martian poles.
Earth is still being struck by stones from space – although a lot less frequently, thankfully – and they provide valuable clues about how the planets formed.
Picture: A NASA artist’s impression of Earth being struck by a giant chunk of space rock.
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