[meteorite-list] 3 Billion-Year-Old Fossils Show Early Microbes Lived in Cavities

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 13 Jan 2016 16:23:22 -0800 (PST)
Message-ID: <201601140023.u0E0NMjk008868_at_zagami.jpl.nasa.gov>

https://www.newscientist.com/article/dn28678-3-billion-year-old-fossils-show-early-microbes-lived-in-cavities/

3 billion-year-old fossils show early microbes lived in cavities
New Scientist
December 16, 2015

It seems the microbes that formed Earth's first ecosystems looked for
shade when the sun was strong, just like we do.

Fossils found in South Africa suggest that cavities in tidal sediments
might have provided refuge from deadly solar rays during the Archaean
aeon when we think that life emerged on Earth.

At this time, between 4 billion and 2.5 billion years ago, Earth was scorched
by intense UV radiation, and had no ozone layer to protect it - a bit
like Mars is today.

So life at the surface would have found survival a challenge.

Some of the oldest fossil cells are around 3.43 billion years old, and
thought to have lived on sand grains that might have been covered by shallow
water and overlying grains.

At the Barberton greenstone belt in South Africa, an area where ancient
volcanic rock has been pushed to the surface, there are thin layers of
rock thought to be 3.22 billion-year-old microbial mats - sheets of microbes
that covered tidal areas of the seashore.

Now fossilised bacteria have been discovered underneath the mat in cavities
covered by a thin layer of sediment. The bacteria are rod-shaped, growing
end-to-end in long filaments like many bacteria do today.

Like modern microbes

"The shape is quite uniform," says co-author Alessandro Airo, whose colleague
Martin Homann at the Free University of Berlin, Germany, analysed the
fossils. "It appears that by that time, they were already able to biochemically
control diameter and length, and coordinate themselves into a chain. That's
what modern microbes do all the time."

David Wacey, a palaeobiologist at the University of Bristol, UK, says
the evidence from the new study looks robust.

'They have studied the geology in detail so we know that the environment
was habitable for life, and the interpreted setting is closely comparable
to where we would expect to find such structures today," he says.

"The record of Archaean microfossils is sparse and controversial," says
Birger Rasmussen at Curtin University, Australia, who previously reported
the discovery of cavity-dwelling microbes in 2.7 billion-year-old sediments
in Australia. "This is an exciting find as it extends the record of possible
life in this habitat a further 500 million years."

The atmosphere and UV radiation during this period of Earth's history
are thought to have been similar to conditions on Mars. Airo says that
understanding how life could have survived in this time could give us
clues about what sort of life might be found on Mars and where to look.

"This study shows that very close to the surface, life was possible back
then," he says, "so it could well be that microbes thrived even on the
surface of Mars and not necessarily only in deep water or the subsurface."

Journal reference: Geology, DOI: 10.1130/G37272.1
Received on Wed 13 Jan 2016 07:23:22 PM PST