A group of researchers from Imperial Collage London, led by Richard Court (Department of Earth Science and Engineering) have found that the climatic conditions on Earth and Mars 4 billion years ago were much colder than previously thought. The cause was an interminable rain of micro-meteorites, the size of sugar grains, that characterised the last phase of accretion of the two planets. This phase is referred to as the Late Heavy Bombardment (LHB).
The ICL researchers reached this conclusion, published last weekend in "Geochimica et Cosmochimica Acta", by simulating in the laboratory the vaporisation of micro-meteorites in the atmosphere using "flash pyrolysis" to heat rocky fragments, similar to meteorites, to 1000°C.
By measuring the amount of gas produced in the experiment, and using
the quantity of micro-meteorites that fell during the LHB, Court and
colleagues found that the amount of sulphur dioxide (SO2)
released into the atmosphere over a period of about 100 million
years, was around 20 million tons per year on Earth, and half a
million tons per year for Mars.
Because sulphur dioxide forms aerosols with both solid and liquid
particles, the atmospheres of both Earth and Mars became more opaque
to sunlight, so that the energy reaching the planetary surfaces was
significantly less than it is today. This situation on Earth may
have provoked an ice age lasting millions of years, that would have
been a serious obstacle to the appearance of microbial life.
To put their calculations in context, Court's team calculated that
the quantity of sulphur dioxide deposited in Earth's atmosphere by
micro-meteorites was equivalent to a 1991 eruption of mount
Pinatubo, every year, for 100 million years.
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