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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]

Platypus (Ornithorhynchus anatinus)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.

Dresser FormationA 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:

  1. 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.
  2. Program Book of the American Geophysical Union 46th annual Fall Meeting, San Francisco, California, 9-13 December, 2013 (PDF File).
  3. Hard rock life, Michigan State University Press Release, December 9, 2013.
  4. 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.
  5. Pilbara home to 3.5 billion-year-old bacterial ecosystems, University of Western Australia Press Release, November 11, 2013.
  6. Evidence of 3.5 billion-year-old bacterial ecosystems found in Australia, Carnegie Institution of Washington Press Release, November 12, 2013.
  7. Jonathan Pearlman, "Oldest signs of life on Earth found," Telegraph (UK), November 13, 2013.
  8. Oliver Milman, "Earliest life on Earth: scientists find evidence in WA rock sediments," The Guardian (UK), November 12, 2013.
  9. 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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