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An important process interconnected with
Earth’s climate history is …
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PLATE TECTONICS
Pangaea Modern Continents
Animation courtesy of U.S. Geological Survey
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Glossopteris FossilPhoto courtesy of U.S. Geological Survey
EARLY SCIENTIFIC HYPOTHESIS - “CONTINENTAL DRIFT”
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Hypothesis : Glossopteris areas were once close together but then
broke apart & moved to the continents’ current positions.
Illustration credit: Peter Bockman
Distribution of Glossopteris plant fossils in Permian (250-299 mybp)
rocks(mybp = million years before
present)
But how do we know this is true?
Are there other possible explanations and
hypothesesfor finding this fossil
plant on widely separated continents?
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Let’s think about this …ACTIVITY 1: Hypothesis Helper
Which of the five species (if any) might provide the
best evidence for tectonic plate
movement?
Which species could have spread between Africa &
South America only if those continents were
once connected?
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Not the species that could have reproduced across the
ocean …
NOPE!
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… but the species that could have spread only on continuous
land which later broke apart
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A - Large triangular leaves; berries commonly
eaten by migratory animals B - Short, narrow, oval leaves; produces fewseeds, reproduces mainly by stolons C - Small thin feathery leaves; large seeds havespongy outer cover, allowing seeds to float andtravel easily in either fresh or salt water D - Thrives in swampy or watery environments;very large, heavy seeds sink and lodge inbottom sedimentsE - Long thin leaves; small fluffy seeds easilycarried by wind
stolons
WOOHOO!You have used ancient plants’ adaptations for reproduction & seed
dispersal (seed transport) to test a hypothesis about tectonic plate
movements!
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HOW DO THE SCIENTISTS KNOW SO MUCH ABOUT THEM?
IF THOSE PLANTS ARE FOSSILS &
ANCIENT & PROBABLY EVEN
EXTINCT …
WHOA!JUST A
SECOND!
I HAVE A QUESTION!
Earth processes that operated in the past are similar to those operating today.
“The present is the key to the past.”
PRINCIPLE OF UNIFORMITARIANISM
(UNIFORMITY)
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So earth scientists study modernvolcanoes to understand ancientvolcanic rocks … And modern rivers, glaciers, deserts,& coastlines and their sediments tounderstand how ancient sedimentaryrocks formed … And modern plants & their adaptationsto understand similar ancient plants &their adaptations.
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Based on its fossilremains and oncertain similaritiesto modern BaldCypress, scientistshave interpreted:
Tree shape & roots like modern bald cypressWarm, very wet environmentsSeeds too fragile to survive a long sea trip
FOR GLOSSOPTERIS, WHICH HAS NO MODERN REPRESENTATIVES
GLOSSOPTERIS
BALD CYPRESS
Illustration credits: Glossopteris, Rose Prevec, Rhodes University (South Africa); bald cypress, NRCS
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