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Solving Charles Darwin's 'Abominable Mystery'

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Solving Charles Darwin's "Abominable Mystery"

Scientists are using chemical fossils to hunt down one of our planet's most vexing missing links -- the first-ever flowering plant.

NASA
Marshall Space Flight Center

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April 17, 2001 -- Daffodils, tulips, roses and other flowers are so much a part of our daily lives that we take them for granted. Yet, how and when flowering plants appeared on Earth remains a mystery, a question that has gone unanswered by evolutionary scientists for more than a century.

According to the fossil record, mosses were the first plants to emerge on land, some 425 million years ago, followed by ferns, firs, ginkgoes, conifers and several other varieties. Then, it seems, about 130 million years ago flowering plants abruptly appeared out of nowhere.

Above: A fossilized flower (left) and a modern flower (right). New evidence suggests such plants may have evolved earlier than previously thought. Credit: Hanman's Fossils

Where did they come from, and how could they have evolved so suddenly without any transitional fossils linking them to other ancient plant species?

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"An abominable mystery" is how nineteenth-century naturalist Charles Darwin referred to the origin of flowering plants, and the puzzle remains as controversial today as ever.

Now a team of Stanford geochemists has entered the debate with evidence that flowering plants may have evolved 250 million years ago - long before the first pollen grain appeared in the fossil record.

"Our research indicates that the ancestors of flowering plants may have originated during the Permian period, between 290 and 245 million years ago," says J. Michael Moldowan, research professor of Geological and Environmental Sciences at Stanford.

"We based our findings on an organic compound called oleanane, which we found in the fossil record," he adds.

"This is important and exciting work," says Bruce Runnegar, professor of paleontology at UCLA and a member of NASA's Astrobiology Institute. "Although this is not the first time such a claim has been made, previous work used details of plant anatomy rather than the biomarker molecule [oleanane]."

Left: The Chemical Structure of Oleanane. Moldowan and his colleagues have detected Oleanane in oily rock deposits that are hundreds of millions of years old. Credit: IUPAC

Oleanane is produced by many common flowering plants as a defense against insects, fungi and various microbial invaders. But the chemical is absent in other seed plants, such as pines and ginkgoes.

Moldowan and his colleagues studied Permian-era sediments that harbored the remains of extinct seed plants called gigantopterids. The same sediments contained molecules of oleanane.

It would seem that gigantopterids, like many present-day flowers, produced oleanane -- an indication that they were among the earliest relatives of flowering plants, concludes biologist David W. Taylor of Indiana University Southeast, a co-author of Moldowan's study.

"This discovery is even more significant because we recently found gigantopterid fossils in China with leaves and stems that are quite similar to modern flowering plants," Taylor notes - further evidence that flowering plants and gigantopterids evolved together, roughly 250 million years ago.

Right: Archaefructus liaoningensis. The leaf-like structures on the stem of this 140 million year old fossil are pods containing the seeds, a characteristic unique to flowering plants. Credit: University of Florida.

Moldowan and his colleagues note that "chemical fossils" such as oleanane can be an important tool for studying the history of life on Earth.

Runnegar agrees. "I would imagine that the jury will remain out on [the origin of flowers] for some time, but this research does open up a new approach to solving this difficult problem." The study should also encourage astrobiologists to seek out similar biomarkers for other significant evolutionary events, he added.

Perhaps one day chemical fossils will help unravel Darwin's abominable mystery once and for all.

Moldowan and his collaborators, research associate Jeremy Dahl and graduate student David A. Zinniker, presented their findings at the annual meeting of the American Chemical Society (ACS) in San Diego on April 2, during a symposium titled, "Biogeochemistry of Terrestrial Organic Matter."

Web Links

Geochemists find evidence that flowers may have evolved 250 million years ago -- Stanford University

Darwin's 'Abominable Mystery' is closer to a solution -- A Cornell botany professor says that, with the discovery of the world's oldest flowering-plant fossil, scientists from China and the University of Florida have made a giant leap toward solving Charles Darwin's "Abominable Mystery," the plant world's missing link.

OLDEST KNOWN FLOWER IN THE WORLD FOUND IN NORTHEAST CHINA -- (Chinese Acedemy of Sciences)

Plant Fossil Record -- This Version 2.2 of the Plant Fossil Record (PFR2.2) database includes
descriptions and occurrences of many thousands of extinct plants.


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