Smoggy skies 'created life on Earth'
By Roger Highfield, Science Editor
Last Updated: 2:00am GMT 11/11/2006
Hazy, smoggy skies on baby Earth could have provided the chemical
building blocks of the very first life on our planet, according to
a study of one of Saturn's moons.
Primordial Earth likely had a layer of atmospheric haze, similar to
the one currently on the moon Titan, that may have served as the
principal reservoir of lifes building blocks, according to the
study in the Proceedings of the National Academy of Sciences.
One of Titans most striking features is its thick hazy layer of
organic aerosols, which arises from chemical reactions between the
methane and nitrogen molecules high in the atmosphere, driven by
ultraviolet light.
Prof Margaret Tolbert at the University of Colorado and colleagues
mimicked Titans chemistry by using UV lamps in various simulated
atmospheres.
The researchers found that a methane-nitrogen mix would produce
multiple types of long-chain hydrocarbons, including some aromatic
compounds such as benzene.
The predicted products match well with some of the known components
observed by the Huygens probe to Saturn. The researchers then added
carbon dioxide gas to the mix to see if conditions that were
probably present on early Earth would produce a similar haze.
"It turns out that organic haze can form over a wide range of
methane and carbon dioxide concentrations," said Prof Tolbert.
"This means that hazy conditions could have been present for many
millions or even a billion years on Earth while life was
evolving."
The researcher calculate that Earth could have produced more
than100 million tons of aerosols each year, and thus these organic
chemicals in the haze could have served as the primary ingredients
for primitive life.
According to co-author Melissa Trainer "As these particles settled
out of the skies, they would have provided a global source of food
for living organisms. We found that you can make a lot of organic
material virtually out of thin air."
In addition to serving as a source of organic material, a haze
layer over Earth could have shielded living organisms from harmful
UV rays and helped to regulate Earths early climate, according to
the study.
The haze may have contributed to the geological record on Earth by
depositing organic carbon into some of the planets most ancient
rocks, said Alexander Pavlov, a co-author of the report at the
University of Arizona.
"Our paper is the first but necessary step which suggests that the
total mass of organics derived photochemically could have been
comparable to the total mass of organics in ancient sediments," he
said.