Geology Reference
In-Depth Information
Decades ago the effort to extract information from the Rhynie plant fossils was nothing
less than heroic. It required the preparation of hundreds of thin slices, each providing a
two-dimensionalviewofacomplexthree-dimensionalobject.Imaginetakingyourfavorite
flower,embeddingitinhardopaqueepoxy,andthentryingtoreproducetheflower'sshape
bycuttingtheepoxyintoflatslicesandreassemblingthewhole.That'swhatthepioneering
Rhynie paleobotanists had to do. What they found was a miniature suite of odd, spindly
leafless plants—the ancestors of our green world.
Kevin Boyce decided to revisit the Rhynie chert, to tease out new information about
Earth'sancientflora.HisstrategywastoanalyzenewlycutandpolishedsectionsofRhynie
fossils, roughly the size and shape of a quarter. We employed an electron microprobe, a
machine that maps out the distribution of chemical elements across a polished rock sur-
face like our glass-mounted sections of chert—a machine familiar to mineralogists but
rarely used by paleontologists. We hoped to see if any of the original plant material had
been preserved. The trick was to tune the microprobe to carbon, an element more common
in life than in hard rocks. We were delighted to find that Rhynie chert fossils are loaded
with carbon—and isotopically light carbon, to boot, a compelling sign of its biological ori-
gin.Thecarbondistributionbeautifullyhighlightsthedistinctivetubularstructuresofthese
earlyvascularplants.Ourfirstpaperoncellular-scalemappingofavarietyofancient plant
fossils, including odd stems and plant spores from Rhynie, appeared in the
Proceedings
of
the National Academy of Sciences in 2001.
Kevin's next step was to see if he could pull any biomolecular information from the
fossils. Could we find actual molecular bits from the original plant tissues? Kevin Boyce
focused on a mysterious twenty-five-foot-tall treelike organism called
Prototaxites,
which
hadbeenthelargestknownlivingthingonlandfourhundredmillionyearsago.Thefossils
of this organism are enigmatic because they seem to lack the same cellular structures of
much smaller coexisting plants. Rather, their “trunks” appear to be composed of intricately
interwoven tubelike structures. Working with my Geophysical Lab colleagues Marilyn Fo-
gel and George Cody, Boyce was able to extract and analyze unambiguous molecular frag-
ments from several
Prototaxites
specimens—fragments quite different from those of the
adjacent plant fossils. His remarkable conclusion:
Prototaxites
was a giant fungus, perhaps
the largest toadstool in Earth's history.
Kevin Boyce's research reinforces the conclusions of the paleobotany community.
Earth's landscape four hundred million years ago was at last green, but in an utterly alien
way. Scrubby, stalklike plants shared the land with towering treelike fungi and a few small
insects and spiderlike animals.
Inventing Leaves
