1 / 25

BAESI

November 12, 2011: THE FOSSIL RECORD: Mass Extinctions Instructor: Jonathan Hendricks Assistant Professor of Paleontology, SJSU, Dept. Geology Email: jonathan.hendricks@sjsu.edu. BAESI.

gretel
Download Presentation

BAESI

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. November 12, 2011: THE FOSSIL RECORD: Mass Extinctions Instructor: Jonathan Hendricks Assistant Professor of Paleontology, SJSU, Dept. Geology Email: jonathan.hendricks@sjsu.edu BAESI

  2. Note: If you wish to print these slides, you will need to first delete the image of the Phanerozoic Diversity curve on Slides 3 and 6 (for some reason, they cause PowerPoint to crash when trying to print).

  3. What Determines the Boundaries? • Slide shows the geological time scale. By: “Dragons flight” (Wikimedia Commons)

  4. Mass Extinctions • It is thought that over 4 billion species have lived on planet Earth, but 99% of them are now extinct. • Extinction is a fact of life; typically balanced by speciation. • Mass extinctions are characterized by the following attributes: • >75% of species go extinct. • Global events. • Extinctions in variety of habitats.

  5. The “Big 5” Data from Barnosky et al. (2011)

  6. The “Big 5” (Or, 6?) Mass Extinctions • Slide shows the geological time scale. By: “Dragons flight” (Wikimedia Commons)

  7. The End Permian Event

  8. Slide shows a map reconstruction of Pangea. Earth at the End of the Permian Pangea Source: Ron Blakey, NAU Geology

  9. 90% marine species (80% genera, 50% families) go extinct. Trilobites,tabulate and rugose corals, many types of brachiopods, many echinoderms, etc. 75% families of land vertebrates. Many plants. “Today’s oceans still reflect the winners and losers of events at the end of the Permian” (Erwin, 2006). Slide shows a photograph of a fossil tabulate coral. The End-Permian Mass Extinction Tabulate Coral

  10. Short answer: scientists are not sure. Any hypothesis must explain extinction patterns in the sea and on land. Many scientists have looked for evidence of an asteroid or comet impact at the Permian-Triassic boundary, but have not produced conclusive results. Siberian flood basalts (called the “Siberian Traps”) may be a likely culprit. What Caused It?

  11. Slide shows a map reconstruction of Pangea, detailing the position of the Siberian Traps and their extent. Siberian Flood Basalts Erupted in region that is now Siberia from about 252 to 251 Ma – almost coincident with P/T boundary (251 Ma). Mass of erupted magma equal to extent of continental U.S. – 4 million cubic kilometers. Pangea Source: Ron Blakey, NAU Geology

  12. Siberian Flood Basalts Possible consequences: • Dust clouds. • Acid rain. • Massive volcanic release of CO2. • Global warming (+ 6º C). As temp. increases, O2 becomes less soluble in water, resulting in anoxic (oxygen-free) conditions in shallow water - may have driven marine extinction. • Warming may have also caused melting of frozen gas hydrates in the oceans, releasing substantial amounts of methane, another greenhouse gas. • Runaway greenhouse effect?

  13. The End Cretaceous Event

  14. Theories About Dinosaur Extinction Many ideas have been put forth to explain the demise of the dinosaurs at the end of the Cretaceous: • Global cooling. • Global warming. • Disease. • Inability to digest flowering plants. • Mammals ate their eggs. • They developed cataracts, went blind, and fell off cliffs. However, any theory seeking to explain dinosaur extinction must also explain other patterns of extinction at the end of the Cretaceous period.

  15. Slide shows photographs of ammonoid fossils and rudist bivalve fossils. Extinction on land: Non-avian dinosaurs. Pterosaurs. Much angiosperm plant life. Extinction in the sea: Ammonoids. Mosasaurs. Plesiosaurs. Most marine plankton. Many invertebrate groups. Patterns of End-Cretaceous Extinction Ammonoids

  16. Iridium and the End Cretaceous Boundary In the late 1970’s, it was discovered that a clay layer (marine) spanning the K-T boundary in Italy had extremely high amounts of the metal iridium. Iridium: Rare platinum-group metal. Does not normally occur in Earth’s crust. Occurs in trace amounts in extraterrestrial rocks and the interior of the earth.

  17. Iridium and the End Cretaceous In 1980, Alvarez and colleagues proposed that a bolideimpact was responsible for the iridium anomaly. Iridium anomaly was subsequently found in over 100 K-T boundary sections (marine and terrestrial) from around the world. Other K-T boundary evidence for an impact includes: • Shocked quartz. • Microspherules. • As the evidence for a bolide impact gathered, some scientists went in search of an impact crater of the appropriate age (~65 Ma).

  18. Meteor Crater, Arizona Meteor Crater, AZ: ~ 1.2 km diameter. Meteorite responsible probably about 50 m in diameter. Age of crater about 50,000 years old. Photograph by Shane Torgerson (Wikimedia Commons)

  19. Slide shows an illustration that detail the position of the Chiczulub crater in Mexico. Chicxulub Crater, Yucatan Peninsula, Mexico: 180 km diameter. Close to 65 Ma. The Smoking Gun? NASA

  20. A Bad Day For Planet Earth The bolideimpactor: Likely a meteor 10 km in diameter. Impact likely released energy equivalence of about 100,000 gigatons of TNT. Tsar Bomba = 1/20 of one gigaton (most powerful nuclear weapon ever tested). Probably about a 13 on the Richter scale (2004 Indian Ocean tsunami earthquake about 9.1 on Richter scale; equivalent to about 100 gigatons of TNT). Photograph by “Croquant” (Wikimedia Commons) NASA

  21. Consequences 1 Fires. • Worst near impact site. 2. Tsunamis. 3. Dust fills atmosphere. • Perpetual night for months. • Collapse of photosynthesis. • Global refrigeration (nuclear winter). • Heat atmosphere by friction during descent. 4. Aerosols fill atmosphere. • Trap solar radiation. • Greenhouse warming.

  22. Consequences • Release of carbon dioxide. • Bolide hit carbonates. • Rapid melting!! • Temperature increase of 4.5-13.5 °C. • Increase lasted few hundred thousand years. • Acid Rain. • Caused by release of sulfur oxides when bolide hit evaporites. Important questions remain. For example, why did non-avian dinosaurs go extinct, but birds, lizards, crocodilians, turtles, amphibians, and mammals survive?

  23. Why Does Extinction Matter? • Extinction marks the end of evolution for the lineage that goes extinct. • From an evolutionary perspective, the consequences of a single species going extinct may be minor for a group with many species. • The extinction of a species within a group with only a few species may be very significant, however.

  24. Gould (1984) “If mass extinctions … [are caused by agents] … so utterly beyond the power of organisms to anticipate, then life’s history either has an irreducible randomness or operates by new and undiscovered rules for perturbations, not (as we always thought) by laws that regulate predictable competition during normal times.” – Stephen J. Gould (1984)

  25. Activity Idea • Ask your students (perhaps in groups) to develop hypotheses about what killed the dinosaurs. • Ask them how they would test their ideas. In other words, if their hypothesis is true, what observations should they expect to make in the fossil/rock record? • Then, present the scientific evidence for a bolide impact. • Other ideas?

More Related