Nov. 7, 2006 — Scant evidence has been left behind about life's rise and spread on
Earth, but scientists re-creating a bit of the planet's primordial
atmosphere in laboratory experiments have found a key clue by
studying another place in the solar system: Saturn's giant moon Titan.
"It's been our model," said University of Colorado researcher
Margaret Tolbert, who headed a team of scientists who brewed a tiny
sample of atmospheric gases that could have enveloped early Earth.
Taking a cue from Titan, which is blanketed by a heavy shroud of
organic haze, Tolbert and her team believe a similar phenomenon
could have been triggered on Earth, even with high amounts of carbon
dioxide.
Previous theories discounted the chance of planetary haze,
which could have served as building blocks for life on Earth because
of the presence of carbon dioxide, Tolbert said.
But an unusual laboratory experiment proved otherwise.
Tolbert and her colleagues recreated Titan's hazy skies by exposing
methane gas to an ultraviolet lamp, then added carbon dioxide gas to see if conditions probably present on early
Earth would have produced a similar organic haze.
"It turns out that organic haze can form over a wide range of
methane and carbon dioxide concentrations," said Tolbert, who
reported her findings in this week's Proceedings of the National
Academy of Sciences.
"This means that hazy conditions could have been present for many
millions or even a billion years on Earth while life was evolving,"
she said.
The haze circling Titan — and possibly Earth in its early years — is
due primarily to ultraviolet radiation from the sun chemically
reacting with methane in the atmosphere.
