Scientists have
found what they think is the oldest fossil on Earth, a remnant of life
from 3.7 billion years ago when Earth's skies were orange and its oceans
green.
In a newly
melted part of Greenland, Australian scientists found the leftover
structure from a community of microbes that lived on an ancient
seafloor, according to a study in Wednesday's journal
Nature .
The discovery
shows life may have formed quicker and easier than once thought, about
half a billion years after Earth formed . And that may also give hope
for life forming elsewhere, such as Mars, said study co-author Martin
VanKranendonk of the University of New South Wales and director of the
Australian Center for Astrobiology.
"It gives us an
idea how our planet evolved and how life gained a foothold,"
VanKranendonk said.
Scientists had
thought it would take at least half a billion years for life to form
after the molten Earth started to cool a bit, but this shows it could
have happened quicker, he said. That's because the newly found fossil is
far too complex to have developed soon after the planet's first life
forms, he said.
In an outcrop
of rocks that used to be covered with ice and snow which melted after an
exceptionally warm spring, the Australian team found stromatolites,
which are intricately layered microscopic layered structures that are
often produced by a community of microbes. The stromatolites were about
.4 to 1.6 inches high (1 to 4 centimeters).
It "is like the
house left behind made by the microbes," VanKranendonk said.
Scientists used
the layers of ash from volcanoes and tiny zircon with uranium and lead
to date this back 3.7 billion years ago, using a standard dating method,
VanKranendonk said.
"It would have
been a very different world. It would have had black continents, a green
ocean with orange skies," he said. The land was likely black because the
cooling lava had no plants, while large amounts of iron made the oceans
green. Because the atmosphere had very little oxygen and oxygen is what
makes the sky blue, its predominant color would have been orange, he
said.
The dating
seems about right, said Abigail Allwood , a NASA astrobiologist who
found the previous oldest fossil, from 3.48 billion years ago, in
Australia. But Allwood said she is not completely convinced that what
VanKranendonk's team found once was alive. She said the evidence wasn't
conclusive enough that it was life and not a geologic quirk.
"It would be
nice to have more evidence, but in these rocks that's a lot to ask,"
Allwood said in an email.
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Online:
Nature:
http://www.nature.com/nature