ODU PROFESSOR FINDS SIGNS OF EARLY LIFE IN SANDY TIDAL FLATS
Sandy tidal flats, such as those on Virginia's Eastern Shore or North Carolina's Outer Banks, hold clues that can help pinpoint the beginning of life on Earth, according to Nora Noffke, Old Dominion University assistant professor of ocean, earth and atmospheric sciences.
Noffke's findings, which were noted in the May 5 edition of Science magazine and were the subject of her paper published in the April edition of the journal Geology, provide some of the sturdiest evidence yet that life colonized Earth's oldest sandy coasts at least 3.2 billion years ago.
Her research comprises a decade of adventures in Germany, France, South Africa and the United States, and it illustrates the debt that scientific advancement owes to creativity, adaptability and tenacity of purpose.
The flurry of recognition she has enjoyed this spring is based on a hypothesis that is, at best, tangential to her early work in science. Hers is a story of a geologist who becomes fascinated with felt-like microbial mats, which are living weaves of tiny organisms, or microbes. These mats can be found today blanketing sandy tidal flats in many coastal areas worldwide. Noffke has discovered occurrences of microbial mats just 30 miles from the ODU campus, near the northern terminus of the Chesapeake Bay Bridge-Tunnel.
Her research builds a persuasive case that similar microbial mats existed in the Early Archean Age more than 3 billion years ago.
In her early education at the University of Tubingen, Germany, Noffke's geological focus was on macroorganisms-or larger critters-that made traces in sands and muds, later preserved as trace fossils in rock.
Her doctoral study at the University of Oldenburg, Germany, however, veered off toward the
relatively new discipline of geomicrobiology. Her Ph.D. adviser, W.E. Krumbein, was "one of the first microbiologists studying the interaction between bacteria and sediment or bacteria and rock," Noffke said.
Although it seems certain that early life on Earth involved tiny organisms, science had to go down difficult paths to look for evidence of life that was both many millions of years old and maybe only a few millionths of a meter long. Until now, only the filigrane fossils of smallest bacteria found in glass-like flintstone, or the "stromatolites," build-ups formed by early photoautotrophic microorganisms, constituted an archive for the investigation of early life.
The work of geochemists and paleobiologists has produced evidence suggesting that life did, indeed, evolve on Earth in the Archean, perhaps as early as 3.8 billion years ago. Nevertheless, the evidence can be disputed-and often is both by scientists and creationists-particularly because fossil evidence can be mimicked by purely physical processes. For example, carbon believed to have organic origins can in fact be inorganic.
Doing fieldwork for her Ph.D. on the sandy tidal flats along the North Sea, Noffke observed microbial mats constructed by cyanobacteria, the same organisms that Krumbein's and others' research linked to stromatolites dating to the Archean Age.
"I thought that if living cyanos are abundant in the modern sandy tidal flats, they must do something in the sediment, such as make traces, and if they make traces, those structures might become preserved," she explained.
To understand her research, the layman should first know how a living microbial mat can affect a sandy tidal flat. One example is the stabilization of loose sand grains by a microbial mat. A microbial mat is coherent like a carpet, and cannot be torn by moving water. Therefore, the sand underneath a microbial mat cannot be disturbed. But where there is a rip or hole in the mat, the exposed sand can become transported away by water rushing over it. The results of this stabilization of sands by microbial mats are specific morphologies-forms or patterns-visible on the tidal surface. For her doctoral thesis, Noffke documented 21 of these structures (microbial traces) on tidal flats of the North Sea. Her first paper on the subject was published in 1996.
The next step was to find evidence of these structures preserved in tidal sandstone (petrified tidal flats). Noffke went to the south of France, to the Montagne Noire near Montpellier, where geological evidence indicates tidal flats existed a few hundred million years ago.
She had enough funds for a four-day search, but by late on the fourth day she had found nothing in the old rock that resembled the microbial mat-related structures she documented by the North Sea. Then, in the evening, with the light of the setting sun illuminating the rocks with a steep angle, she discovered a slab of rock with a ripple pattern that looked precisely right. "I saw the ripples in a sudden moment and shouted, 'Yes, that's them!'" she said.
Her revelations, published in 2000, came out simultaneously with similar findings of a research group at the University of Southern California. Noffke had not known that the group had been investigating the same hypothesis. Together, the two published reports spawned a new term for science: "microbially induced sedimentary structures."
Noffke did not rest on her accomplishment. She wanted to survey a region with sandstone that is older than that in the Montagne Noire. During her postdoctoral research as guest of Harvard University geology professor A.H. Knoll, she visited the 600-million-year-old Nama Group in Namibia, Africa. Shortly after joining ODU in 2002, she launched a 10-day expedition to the Pongola region of South Africa. This time, as her script seemed to dictate, she found no samples until the 10th day.
"We had several hundred square miles to survey for a structure that might be just a few square
inches in size. We had 10 days' time, but no luck until on the last day. At 4 p.m., without much hope left, I decided to just take a last look at some exposed rocks near a lake. And here we found a rock with a wrinkle structure, just about 3 x 8 inches wide."
The offshoot of this discovery was a 2003 article in Geology that placed cyanobacteria potentially back as far as 2.9 billion years.
A fortuitous meeting between Noffke, Virginia Tech geologist Kenneth Eriksson and paleobiologist Ed Simpson from Kutztown University led to Noffke's next expedition to South Africa in 2004, this one to the Barberton greenstone belt near Swaziland. Eriksson is not an expert in microbially induced sedimentary structures, but once he became familiar with Noffke's research, he knew just where to look for the structures.
A variety of geological clues can pinpoint where ancient, sandy tidal flats existed, Noffke explained. Eriksson, who has taken many research trips to South Africa, was able to identify a relatively compact search area in the Barberton belt, and on this expedition the researchers were able to find samples right away. These were the samples dated to 3.2 billion years ago, and which led to the April 2006 article in Geology and the May 2006 "Editor's Choice" news article in Science magazine.
Noffke is first author of both the 2003 and 2006 papers in Geology, the latter of which was co-authored by Eriksson, Robert Hazen of the Carnegie Institution's Geophysical Laboratory and Edward Simpson of Kutztown University's Department of Physical Sciences.
The Science article called Noffke's latest discovery of fossil microbial mats "direct evidence" that life evolved on Earth during the Early Archean Age. It added, "Analysis of the carbon isotope compositions of the laminations further supports their bacteria origin. Concentration of these features at the top of sedimentary sequences formed in shallow water environments suggests that the microbes in the mats may have derived their energy through photosynthesis."
In the April paper in Geology, Noffke noted that the oxygen content of the atmosphere prior to 3 billion years ago is not known. It may have been very low. "Photosynthesis of the ancient microbial mats inferred in this study may have been nonoxygenic," the paper explained, "but if microbial communities of this type were oxygenic, then for hundreds of millions of years, such photosynthetic systems may have provided a steady, yet rapidly consumed source of oxygen-a source that would gradually come to dominate the atmospheric chemistry of Earth."
Noffke knows some will question her findings. But she said she and her co-workers have lined up five levels of proof, showing, for example, that the petrified structures she has identified in rocks are found only where ancient tidal flats existed. The structures exactly match those in modern sandy tidal flats produced by microbial mats.
She also has proof from the carbon isotope tests to show that the carbon in her samples is organic, as well as proof from thin sections of the ancient structures in which the bacterial filaments of the microbial mats can be seen.
She said she does not anticipate confrontations with critics whose religious beliefs place Earth as only thousands of years old, not billions. "I always tell my students to consider the ancients' conception of time. The ancients had a different relation to time. How were they able to measure seconds, or to understand the duration of 100 years, let alone the duration of a billion of years-way above the experience of a person's lifespan? For them, the Biblical saying 'seven days' could have meant simply a long, long time for something to be made that takes longer than a worker's day. Indeed, believers in creationism and evolution can agree on the order of creation described in Genesis-of the land, the ocean, and then all critters within."
This article was posted on: May 24, 2006
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