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Undergrad Finds Clues to 400- Million-Year-Old Mystery

Moss or lichen? Steven Porter (with Hope Jahren) helped identity a 400-million-year-old fossil.
Baltimore - Mar 14, 2002
Undergrad Finds Clues to 400- Million-Year-Old Mystery Steven Porter, a Johns Hopkins University senior from Cherry Hill, N.J., has conducted original research that adds new and potentially decisive evidence to a debate about the identity of one of the first organisms to make the epochal leap from the sea to dry land approximately 400 million years ago.

Through a Web site devoted to undergraduate research opportunities at Johns Hopkins, Porter connected with Hope Jahren, an assistant professor in the Department of Earth and Planetary Sciences in the university's Krieger School of Arts and Sciences.

Jahren's lab analyzes isotopes of elements like carbon, nitrogen and oxygen in living and fossilized plants to better understand their relationship to contemporary and prehistoric climates. Isotopes are forms of an element that differ only by the addition of one or more subatomic particles known as neutrons. Different isotopes of the same element have different mass, which affects the way plants use them.

Porter chose to study a unique, high-quality fossil specimen of Spongiophyton minutissimum from Jahren's collection of fossils. Kept in a sealed vial, the specimen is a little bigger than a dime and dates from the Devonian Period, a time about 400 million years ago when the seas of Earth teemed with life but the continents were barren wastelands.

"Now, look at that morphology [shape]," Jahren asks when showing the fossil sample to a visitor. "It's very tough to get much insight into what type of organism this was based solely on its shape, but a look at certain aspects of its chemistry that have been preserved in the fossil may help give us more clues."

Whatever it is, Jahren notes, the sample probably represents a crucial step from life at home only in the sea to the types of life that could spread over land over the course of millions of years.

To learn more about the fossil, Porter resolved to compare it to its nearest modern relatives. But based on studies of the shapes of various fossil samples of Spongiophyton minutissimum, paleontologists were divided into two schools of thought on what those nearest relatives were.

Some thought the fossil was an example of a bryophyte, a class of plants comprised mostly of mosses; and some favored the idea that the fossil was a lichen, which is a close association between a fungus and an alga.

Porter conducted an extensive literature search to familiarize himself with the debate, and then sought the advice of experts in the field to further firm up his understanding. He relishes the fact that he was able to use his inexperience in the field to get a chance to speak with prominent people in it.

"My naivete paid off," Porter says. "I probably would have been much more intimidated talking to these people, since they are very much the leaders of their fields."

Thanks in part to the advice and assistance of people like Paula DePriest, an associate curator in the department of botany at the Smithsonian Institution, Porter was able to select a range of contemporary species of mosses and lichens to test with the fossil.

Using training and equipment from Jahren's lab, he looked at the isotopes of carbon found in each group and in the fossil, and found that the types of carbon in the fossil more closely resembled those found in modern lichens.

"It's very clear from these results that the fossil cycled carbon in a manner that much more closely resembles that of the lichens than it does the bryophytes," Jahren comments.

"Why does that matter? This is one important piece of how we go from sterile land to what we have today. This tells us the type of biology that was most effective, at the very beginning, was the strategy of the lichen, not the moss."

Porter and Jahren hope to present the results at an upcoming meeting of the Geophysical Society of America. Both agreed that Porter has come away with valuable insight into what the process of scientific research is like.

"He's learned that it's labor-intensive work, but that there's a lasting effect to birthing a new piece of knowledge," Jahren says. "I think he also recognizes as a result of his provost project the amount of luck, in addition to good planning, that goes into research."

Ancient Fossil Confirmed
Meanwhile UCLA paleobiologist J. William Schopf and colleagues have substantiated the biological origin of the earliest known cellular fossils, which are 3.5 billion years old. The research is published in the March 7 issue of the journal Nature.

Schopf and a team of scientists at the University of Alabama, Birmingham have devised a new technique using a unique laser-Raman imaging system that enables them to look inside of rocks and determine what they are made of, providing a molecular map.

"This new technique is a tremendous breakthrough, and is something we have sought for 25 years," Schopf said. "Because Raman spectroscopy is non-intrusive, non-destructive and particularly sensitive to the distinctive carbon signal of organic matter of living systems, it is an ideal technique for studies of ancient microscopic fossils. Raman imagery can show a one-to-one correlation between cell shape and chemistry, and prove whether fossils are biological."

Schopf and his colleagues applied the new technique to ancient fossil microbe-like objects, including the oldest specimens reported from the geological record.

"There is no question at all that we have substantiated the biological origin of the oldest fossils now known," Schopf said. "We have established that the ancient specimens are made of organic matter just like living microbes, and no non-biological organic matter is known from the geological record. In science, facts always prevail, and the facts here are quite clear."

In addition to being a paleobiologist, Schopf is also a geologist, microbiologist and organic geochemist. Director of UCLA's Center for the Study of Evolution and the Origin of Life, Schopf was awarded the 2000 Phi Beta Kappa Award in Science for his book, "Cradle of Life: The Discovery of Earth's Earliest Fossils" (Princeton University Press). The annual award is presented for "outstanding contributions" to the literature of science.

As an honors student at Oberlin College in Ohio in the 1960s, Schopf learned in great detail about the most recent 500 million years of the planet's history. But geologic time covers more than 4.5 billion years, and Schopf's textbooks and professors taught virtually nothing about the Earth's first four billion years.

The reason this period was neglected, Schopf learned, was that nobody knew much about it. He vowed to fill that black hole of knowledge, and he explained in "Cradle of Life" how he and other scientists succeeded in doing so.

He is editor of "Earth's Earliest Biosphere" and "The Proterozoic Biosphere: A Multidisciplinary Study," companion books that provide the most comprehensive knowledge of more than 4 billion years of the Earth's history, from the formation of the solar system 4.6 billion years ago to events half a billion years ago.

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