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Bacterial Microfossils
January 8, 2014
Instruction in
evolution from
high school through
college will always mention the
Platypus as an example of an isolated
species. Students are unlikely to forget the platypus, and there are some
cartoon platypi that serve as a reminder. The platypus is a
monotreme that existed only on the
continent of
Antarctica, and now on
Australia, which separated from Antarctica.
Early
biologists had a hard time trying to place the platypus in the
traditional taxonomy because it has a combination of
reptilian and
mammalian characteristics. It has
fur, a
duck bill, the
females lactate and
lay eggs, and the
males produce a reptilian
venom at ankle spurs. Evidence from
fossils and
molecular biology place the platypus as existing from 166 million years ago, isolated over all those years.[1]
The platypus
(Ornithorhynchus anatinus)
(Photo by Dr. Philip Bethge, via Wikimedia Commons.)
Contrast the isolated evolution of the platypus with the universality of what would appear to be quite isolated
bacterial species, as reported by
geomicrobiologists,
Matthew Schrenk of
Michigan State University,
Julie Huber of the
Marine Biological Laboratory,
T.C. Onstott of
Princeton University, Merja Itavaara of
VTT Finland and
Ramunas Stepanauskas of
Bigelow Laboratories. A summary of their
research was presented at the
American Geophysical Union Fall Meeting, 9-13 December, 2013, in
San Francisco,
California.[2-3]
The research team found that bacterial specimens, collected from hardened
rock found
miles deep inside the
Earth, are similar, no matter where in the world they are collected. Microbial specimens were collected from deep locations in California,
Finland and
South Africa; and from deep
hydrothermal vents in the
Caribbean Sea.[3]
Says team leader, Matthew Schrenk,
"...We're seeing the same types of organisms everywhere we look... it challenges the imagination to think of nearly identical microbes 16,000 kilometers apart from each other in the cracks of hard rock at extreme depths, pressures and temperatures."[3]
Such extant bacteria are interesting objects for study, but equally interesting is research into the
fossil remains of ancient bacteria. A recent example of such research was conducted by
scientists from the
Old Dominion University (Norfolk, Virginia), the
University of Bergen (Bergen, Norway), the
University of Western Australia (Perth, Australia), and the
Carnegie Institution for Science (Washington, DC).[4-9]
What they discovered, in the remote
Pilbara region of
Western Australia, was evidence of Earth's earliest life, existing 3.2-3.45 billion years ago.[4] This was fossil remains of bacteria in
sedimentary rock in the
Dresser Formation, west of
Marble Bar, in Western Australia.[5,7-8]
This discovery pushes back the known start of life on Earth by 300 million years.[5-6] The evidence is
microbially induced sedimentary structures (MISS) in which sediment co-deposit with
microbial mats. Such structures are common even today in
tidal flats,
lagoons,
lakes and
shores.[4]
Such finds are rare, since the geologically active Earth tends to erase such evidence through
hydrothermal and
tectonic activity.[5,6,9] The geology of the Pilbara region of Western Australia is unique in having very old, but very pristine, sedimentary deposits. It's known for its wealth of early specimens, including
stromatolites, ancient
photosynthetic bacteria.[5,6,9] Now, MISS specimens can be added to the list.
A sedimentary rock from the 3.48 billion years old Dresser Formation, Pilbara region, Western Australia.
The surface cracks are indicative of its biological origin.
(Carnegie Institution photo by Nora Noffke.)
At the time the Pilbara bacteria flourished, the Earth was a far different place. Global temperature was higher, there was almost no
oxygen, with the
atmosphere containing much more
methane and
carbon dioxide, instead.[8] Most of the world was
water, there were few landforms, and many
volcanoes.[8]
Bacteria themselves were not found, but rather
chemical evidence of their existence. The MISS deposits are sediments that were glued together by the microbes.[5,8]
David Wacey, an author of the work from the University of Western Australia, is quoted by
The Telegraph as saying,
"We see tufts and wrinkles and – when we look down the microscope – we see filaments tangled in sand grains. We are also seeing organic material which are the actual microbes but they are decomposed to the point that we cannot see an actual cell. You just see a mass of carbon-rich material."[7]
These results are scheduled for publication in
Astrobiology, so there's an
astrobiological link. The
Mars rovers are looking for similar biological evidence on Mars.[5,6] The Pilbara microbial mats could be seen by a Mars rover.[7]
Since the Dresser MISS resembled specimens resembled those of a 2.9 billion years old deposit in
South Africa, further work is expected at that location.[6,8,9] There are claims of finding traces of older life in
Greenland, but those rocks have been considerably deformed, and the evidence is not as clear as for Pilbara.[7]
The work was funded by the
National Science Foundation, the
NASA Astrobiology Institute, the
NASA Exobiology and Evolutionary Biology Program, and the
Carnegie Institution for Science.[6]
References:
- Wesley C. Warren, et al., "Genome analysis of the platypus reveals unique signatures of evolution," Nature, vol. 453, no. 7192 (May 8, 2008), pp. 175-183.
- Program Book of the American Geophysical Union 46th annual Fall Meeting, San Francisco, California, 9-13 December, 2013 (PDF File).
- Hard rock life, Michigan State University Press Release, December 9, 2013.
- Nora Noffke, Daniel Christian, David Wacey and Robert M. Hazen, "Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia," Astrobiology, Online Ahead of Print, November 8, 2013, doi:10.1089/ast.2013.1030; PDF at http://online.liebertpub.com/doi/pdf/10.1089/ast.2013.1030.
- Pilbara home to 3.5 billion-year-old bacterial ecosystems, University of Western Australia Press Release, November 11, 2013.
- Evidence of 3.5 billion-year-old bacterial ecosystems found in Australia, Carnegie Institution of Washington Press Release, November 12, 2013.
- Jonathan Pearlman, "Oldest signs of life on Earth found," Telegraph (UK), November 13, 2013.
- Oliver Milman, "Earliest life on Earth: scientists find evidence in WA rock sediments," The Guardian (UK), November 12, 2013.
- Russell Westerholm, "3.5 Billion-Year-Old Ecosystem Discovered in Australia Sedimentary Rock; How It Could Aid Space Exploration," University Herald, November 13, 2013.
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