Copyright 2009
An important process interconnected with Earth’s climate history is …
Copyright 2009 PLATE TECTONICS Pangaea Modern Continents Animation courtesy of U.S. Geological Survey
Copyright 2009 Glossopteris Fossil Photo courtesy of U.S. Geological Survey EARLY SCIENTIFIC HYPOTHESIS - “CONTINENTAL DRIFT”
Copyright 2009 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 ( mybp) rocks (mybp = million years before present)
But how do we know this is true? Are there other possible explanations and hypotheses for 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?
Copyright 2009 Not the species that could have reproduced across the ocean … NOPE!
Copyright 2009 … but the species that could have spread only on continuous land which later broke apart
Copyright 2009 A - Large triangular leaves; berries commonly eaten by migratory animals B - Short, narrow, oval leaves; produces few seeds, reproduces mainly by stolons C - Small thin feathery leaves; large seeds have spongy outer cover, allowing seeds to float and travel easily in either fresh or salt water D - Thrives in swampy or watery environments; very large, heavy seeds sink and lodge in bottom sediments E - Long thin leaves; small fluffy seeds easily carried by wind stolons
WOOHOO! You have used ancient plants’ adaptations for reproduction & seed dispersal (seed transport) to test a hypothesis about tectonic plate movements!
Copyright 2009 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)
Copyright 2009 So earth scientists study modern volcanoes to understand ancient volcanic rocks … And modern rivers, glaciers, deserts, & coastlines and their sediments to understand how ancient sedimentary rocks formed … And modern plants & their adaptations to understand similar ancient plants & their adaptations.
Copyright 2009 Based on its fossil remains and on certain similarities to modern Bald Cypress, scientists have interpreted: Tree shape & roots like modern bald cypress Warm, very wet environments Seeds 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