Fossils as Clues / Post Lab Was Wegener Correct??? At any given moment, every place on Earth is either erosional or depositional. The geologic history of the Earth is written in layers of sedimentary rocks. • Deposition of sediments records (writes) history. • Erosion erases records that were previously written. • Geologists can open the book to read by drilling core samples and examining rock columns. What does finding coal in Antarctica tell you? • Antarctica was once warm and rainy with swamps. • How could that be? • Either the whole world was once warmer (global warming) or • Antarctica used to be located near the Equator (AND IT MOVED SINCE THEN!) What does finding two different places with the same sequence of sedimentary rocks tell you? • They both had the same sequence of environments (and environmental changes.) (BUT, Not necessarily at the same time.) If two places have rocks indicating that the same things happened in each (for example - an ocean dried up), how would you know if both happened at the same time? FOSSILS What about present and past plants and animals? • Today, there is a rule in biology that says that each continent has its own land plants and land animals. • Fossils tell us that India, South America, Antarctica, and South Africa all had the same plants and animals at one time. • WAS THE RULE BROKEN? • Why or why not? OK - So why did we do all of this???? • Alfred Wegener said that it wasn’t a coincidence that the continents look like pieces of a jigsaw puzzle. • He thought that the continents had, at one time, all been connected. • Most other geologists thought that Wegener was wrong. • Wegener started to gather evidence to support his hypothesis. • Now we will review some evidence and the conclusions you can draw from this evidence. TEST! Evidence 1. 2. 3. 4. Conclusion EVIDENCE - CONCLUSION • 1. Some continents have rocks that indicate that they once had environments very different from environments those continents have today. • For example - Antarctica has coal. • Antarctica was once near the Equator (when it formed coal) and has since moved to the South Pole. • Therefore, CONTINENTS CAN MOVE! EVIDENCE - CONCLUSION • 2. Sedimentary rocks in rock columns show that continents that are now widely separated had the same sequence of environments. • India, Antarctica, South Africa, and South America were once connected and so, share the same history. EVIDENCE - CONCLUSION • 3. Fossils in the sedimentary rocks tell us that not only did these continents have the same sequence of environments, they each had the same environment at the same time. • This is additional evidence that India, Antarctica, South Africa, and South America were once connected. EVIDENCE - CONCLUSION • 4. Today, each continent has its own land plants and land animals. (A rule!) Fossils show that many of today’s continents once had the same plants and animals. • India, Antarctica, South Africa, and South America were once connected. The rule wasn’t broken because there was only one continent (and it had its own plants & animals.) How do geologists know what environments existed in the past? • • • • Sedimentary Rocks! Coal = swamps Sandstone = beach, dunes, or riverbank Limestone = deep ocean How do geologists know when things happened? • Fossils! • Certain plants and animals only lived on Earth for a short period of time. • If you find a fossil of one of those organisms in a rock layer, you know how old that layer is. • Lystrosaurus was early Triassic. You find several layers of sand exposed in a river bank. Which is the oldest layer? • The one on bottom. • You know this because of the principle of superposition.