JHU geophysicist earns honors

Last week, the American Geophysical Union awarded Johns Hopkins associate professor A. Hope Jahren with the James B. Macelwane Medal. Established in 1961, the Macelwane medal is given annually to scientists younger than 36 for their accomplishments in geophysics.

Jahren's research has also earned her the Donath Medal, making her the first woman to receive both of these prestigious honors.

For Jahren, however, the great part of her research, focused on the role of carbon in ancient ecosystems, is that she gets to do what she loves.

One project that has recently put Jahren at the forefront of geophysics is her use of carbon analysis to put new perspective to a problem that has been plaguing paleontologists for decades.

This age-old division between some scientists is all thanks to one tiny fossil.

Fossil hunters on many continents have dug up remains of spongiophyton minutissinum, but despite its widespread and common nature, paleontologists have never been able to agree on what class of organism the fossil belongs to.

Some think that this tiny fossil is a plant, more specifically a member of the family that we know as modern day mosses. Others think that this fossil belongs to an entirely different kingdom on the tree of life; they believe that it is lichen, a combination of a fungus and bacteria.

Jahren, when entering this debate, did not feel strongly one way or another, and she believes this unbiased view helped her research greatly. She decided to take advantage of carbon, a chemical element, to figure out which kingdom the mysterious fossil belongs to.

As Jahren puts it, "all carbon was not created equal," and she used this natural phenomenon to her advantage. About one percent of all the carbon in the universe is carbon-13, a form of compound slightly heavier than the normal form, carbon-12. Biological processes affect these two forms of carbon slightly differently and Jahren suspected that they could be processed differently in mosses and lichens because the two have different ways of getting carbon into their systems.

To test this hypothesis, Jahren gathered dozens of modern day mosses and lichens and tested the ratio of the two forms of carbon present in them. Much to her advantage, she discovered that lichens have a higher proportion of carbon-13, the heavier form, than mosses do.

Returning to the mysterious fossil which she set out to analyze, Jahren found that the ratio of its two forms of carbon fit almost exactly with the ratio that she had calculated for modern day lichens. Therefore, she concluded that spongiophyton minutissinum was lichen.

This has implications in what scientists believe the world was like 408 million years ago, when spongiophyton minutissinum was present. If this widespread organism were a moss, it would suggest a swampy planet. Lichens can survive much harsher conditions and temperatures however, and thrive in dry areas, suggesting that the planet was perhaps less marshy than people believe.

Though many scientists still believe that the argument is far from over, Jahren thinks that she made a valiant effort. After all, she says that what she is really trying to do is "reinvent paleontology using chemical methods," and this is just what she succeeded in doing.

Besides identifying fossils using carbon dating, Jahren is currently using additional carbon records to characterize changing atmosphere and weather patterns in ancient times.

Jahren has been an associate professor of Earth and Planetary Science at Johns Hopkins since 1999. Before this, she did research at UC Berkeley and Georgia Tech.

In addition to Jahren, geophysicists Paul Asimow and James T. Randerson of Caltech have also been awarded the Macelwane Medal this year.