State Framework(s)/Common Core Objective(s):
Earth and Space Science, Earth’s History, Grades 6-8, #7. Explain and give examples of how physical evidence, such as fossils and surface features of glaciation, supports theories that the earth has evolved over geologic time.
Using a field guide and models of the five southern continents, students will be able to (SWBAT) collect fossil evidence for an investigation on Pangaea on their data tables.
Using the fossil evidence collected, SWBAT analyze their fossil evidence and complete analysis questions in the analysis packet.
Using glaciers and glacial grooves, SWBAT explain how glaciers move and how glacial grooves can be used to reconstruct the way the continents were connected in the past.
Theory of Continental Drift – in 1911, Alfred Wegener noticed that the continents appeared to once fit together like puzzle-pieces. He also found evidence of identical plant and animal fossils on continents that were separated by oceans. This evidence made Wegener think about how this could happen and he proposed the idea that the continents may have once been all connected in a supercontinent he called Pangaea (Pan = all, Gaia = Earth). He realized the continents must be drifting or moving across the oceans. Wegener had lots of evidence, but unfortunately, he could not explain the mechanism for why the continents were drifting. For this reason, many people found his theory to be too incredible to believe.
Four Types of Evidence that support Wegener’s Theory of Continental Drift
- Shape of continents (puzzle-pieces) – The coastlines of several continents appear to fit together very well, such as South America and Africa. This suggests that the continents may have been connected at one time in Earth’s history.
- Fossil evidence – Fossils of the same organisms have been discovered on continents separated by oceans. This means that either the organism evolved exactly the same on two continents at the same time (unlikely), the organisms were able to swim or fly across an ocean (unlikely), or the continents used to be connected and have now drifted apart (likely). New research and evidence shows that the continents have indeed drifted apart.Wegener proposed that the organisms had lived side by side, but that the lands had moved apart after they were dead and fossilized. His critics suggested that the organisms moved over long-gone land bridges, but Wegener thought that the organisms could not have been able to travel across the oceans. Fossils of the seed fern Glossopteris were too heavy to be carried so far by wind.
Mesosaurus was a swimming reptile, but could only swim in fresh water.
Cynognathus and Lystrosaurus were land reptiles and were unable to swim.
- Glacial evidence – Glaciers record marks, called glacial grooves, in the Earth’s bedrock as they move outward. Scientists can use these grooves to reconstruct the previous relative location of each continent that shared a glacier
Grooves and rock deposits left by ancient glaciers are found today on different continents very close to the equator. This would indicate that the glaciers either formed in the middle of the ocean and/or covered most of the Earth. Today, glaciers only form on land and nearer the poles. Wegener thought that the glaciers were centered over the southern land mass close to the South Pole and the continents moved to their present positions later on.______________________________________________
- Rock evidence – Wegener discovered that identical rocks could be found on both sides of the Atlantic Ocean. These rocks were the same type and the same age. Wegener understood that the rocks had formed side-by-side and that the land has since moved apart. Wegener also matched up mountain ranges that had the same rock types, structures, and ages, but that are now on opposite sides of the Atlantic Ocean. The Appalachians of the eastern United States and Canada, for example, are just like mountain ranges in eastern Greenland, Ireland, Great Britain, and Norway. Wegener concluded that they formed as a single mountain range that was separated as the continents drifted.
Alfred Wegener Battle Rap (Music makes a great learning tool!)
LEARN MORE: Here is a link to read about Continental Drift in the online textbook: http://www.ck12.org/earth-science/Continental-Drift/lesson/Continental-Drift/r23/