Evolutionary Leap From Sea To Dry Land: Undergrad Finds Clues To 400-Million-Year-Old Mystery

As one of 42 Johns Hopkins students who received Provost's Undergraduate Research Awards in the 2001-2002 academic year, Porter will present an overview of his project during an upcoming awards ceremony. It will run from 3 p.m. to 6 p.m. on Thursday, March 7, in the Glass Pavilion on the Homewood campus, 3400 N. Charles St., in Baltimore.

Although he’s a pre-med student majoring in English, Porter sought out an undergraduate experience in laboratory research that would allow him to explore areas beyond his training in molecular biology and cellular biology. Through a Web site devoted to undergraduate research opportunities at Johns Hopkins, he 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.”