A shower of millions of rocks from space that collided with Mars, the Earth, and the moon about four billion years ago could have warmed our planet and made it wetter, say researchers. That's what scientists found when they heated ancient rocks like those that hit the Earth billions of years ago and measured the carbon dioxide and water that was released, according to a study published in the journal Geochimica et Cosmochimica Acta. Scientists have long suspected that the necessary materials for life could have come from outer space, and the study suggests how and when the Earth might have received these life-giving ingredients. During the 20-million-year-long meteor shower known as the Late Heavy Bombardment, the rocks that hurtled towards Earth would have been heated to extremely high temperatures as they entered the atmosphere.
According to the scientists' theory, the frictional heat of passing through the thin atmosphere that surrounded the Earth at that time would have been enough to strip the oxygen- and water-rich outer layers from the meteorites as they plunged toward the planet. That process would slowly have caused a buildup of oxygen and water in the atmosphere [Los Angeles Times].
t a rate of 20,000 degrees Celsius per second, the researchers heated samples of ancient rocks remaining from the bombardment in the absence of oxygen to prevent combustion. They then measured the gases released when the rocks were heated. The scientists 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 [Scientific American]. Although that amount is too minuscule for just a meteor or two to have an effect on the Earth's composition, records reveal that the Late Heavy Bombardment dumped millions of rocks on Earth and Mars. 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 [Scientific American].
That amount of carbon dioxide could have started a greenhouse effect to warm up the planet, researchers hypothesize. According to lead author Richard Court, the scientists' data
"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" [Astrobiology Magazine]. But if both Mars and Earth were bombarded by the meteorites, why isn't Mars' atmosphere more conducive to life? Unlike Earth, Mars doesn't have 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. A reduction in volcanic activity also cooled the planet. This caused its liquid oceans to retreat to the poles where they became ice [Astrobiology Magazine].
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Image: flickr/ johnlemon