[meteorite-list] Getting warm and wet from meteorites

[Darren Garrison]

http://blogs.discovermagazine.com/80beats/2009/06/08/study-20-million-year-meteorite-shower-turned-earth-warm-wet/

Study: 20-Million-Year Meteorite Shower Turned Earth Warm & Wet

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]. At 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