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Plants spread secrets about climate change
The once-secret lives of plants are telling researchers volumes about the composition of Earth's atmosphere, providing clues to past and current climate change.
" ... Plants en masse reflect the chemistry of the atmosphere," said Hope Jahren, assistant professor of earth and planetary sciences at Johns Hopkins University. "(Our study) suggests that we will be able to use the composition of fossil plant tissue to reconstruct the carbon composition of past atmospheres as far back as 400 million years ago," she added.
Jahren co-authored a paper containing these findings for the journal Paleobiology. The report has only fueled her interest in more research. "Land plants have existed for about 400 million years and if you know where to look, you can find remains of fossil plant material from each of the ancient periods," said Jahren.
Researchers from Johns Hopkins and the University of California at Berkeley found evidence in data collected from 176 thriving plant species that fossil plants can help scientists determine sources of carbon in the atmosphere hundreds of millions of years ago. The group studied so-called "C3" plants, the most prevalent type of plant life on Earth for the past 400 million years. C3 plants include all trees and some grasses.
"We have tested a wide variety of plants in a wide variety of modern conditions, including drought, heat, altitude and high greenhouse gas levels. We feel that this exhausts the range of environments that plants have known on Earth during the past 400 million years. Therefore, the results of the modern study are applicable to ancient times," Jahren said.
"Our research sheds light on the potential sources and sinks of carbon in the atmosphere but doesn't tell how much carbon there was in the atmosphere. Several other techniques exist toward that assessment," Jahren said.
A carbon sink such as photosynthesis takes carbon out of the atmosphere. A source such as fossil fuels and volcanoes puts the element into the atmosphere.
"The next step in our research is to go to strategic places in the fossil record ... where we suspect climate change and use our method to assess whether a disruption in carbon cycling is apparent," Jahren said.
Meanwhile, the young researcher is busy isolating and analyzing plant fossil material. "We use classic microscopic techniques in conjunction with high-tech chemistry," she said. "Right now we are focusing on three time periods: the Early Cretaceous (about 114 million years ago), the late Cretaceous (about 65 million years ago) and the middle Eocene (about 45 million years ago.) We have fossil plant samples from both North and South America for these periods."
Jahren's colleagues in the study include lead author Nan Arens, assistant professor of integrative biology at the University of California, and Ronald Amundson, professor of soil science at the University of California.
A related study by Robert Berner of Yale University suggests that an increase in oxygen more than 300 million years ago was caused by the growth and spread of trees and other vascular land plants.
The new plant life produced dead organic matter resistant to decomposition. The organic matter gave rise to increased global photosynthesis, which pumped more oxygen into the atmosphere, according to Berner, a professor of geology and geophysics at Yale.
"The rise of large vascular land plants had a significant effect on atmospheric composition, both oxygen and carbon dioxide," Berner said.
Published in the March 3 issue of Science, Berner's study shows that the high oxygen levels during this period verify previous estimates. It also suggests that the oxygen event may have been a key factor in the evolution of huge insects.
"As a result of these experiments, we were better able to calculate realistic changes in atmospheric oxygen over geologic time," Berner said.
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