Earth Systems 3209

1. Earth Systems 3209 Reference: Chapters 6, 8; Appendix A & B Unit: 2Historical Geology

2. Unit 2: Topic 4.3 Mass Extinctions Focus on . . . • relating the divisions of geologic time with two major mass extinctions in the geologic past.

3. Mass Extinctions in the Geologic Past: • Mass extinctions are episodes in geologic history where mass amounts of organisms (species) are killed off. • Two major periods of extinction is recognized in Earth’s history • Permian – Triassic Boundary (End of Paleozoic) • Cretaceous – Tertiary (K-T) Boundary (End of Mesozoic) Text Reference:page 238

4. Mass Extinctions in Geologic Past: • The most widely accepted hypothesis for the extinction at the end of the Paleozoic Era, is the plate tectonic assembly of Pangaea which resulted in a loss of habitat. • The most widely accepted hypothesis for the extinction at the end of the Mesozoic Era, is the impact of a great meteorite and the corresponding disruption of climate. • Other possible explanations;1. falls in sea levels;2. climatic changes;3. prolonged volcanic eruptions;4. periods of a lack of oxygen in oceans.

5. Permian-Triassic Boundary (End of Paleozoic): • Possible explanation is the plate tectonic assembly of Pangaea approximately 245 - 200 million years ago. • Marked the greatest death of species recorded in the fossil record. • 95% of all living species were killed off. • Trilobites and brachiopods are two species that died out.

6. Permian-Triassic Boundary (End of Paleozoic): • Main reason was loss of habitat.Collision of four land masses caused an increase in elevation of land (mountain building) causing drier and colder climates where organisms can not survive. Also, this reduced the area of continental margins by 50% and dropped sea levels by 100 meters thus reducing the living habitat for marine life to approximately 25% of the original. The living space for shelf marine life was thought to be reduced by as much as 75%.

7. Cretaceous-Tertiary Boundary (End of Mesozoic): • Possible explanation is the great meteorite impact approximately 66 million years ago. • Marked one of the largest death rates of species recorded in the fossil record. • 77% of all living species were killed off.

8. Cretaceous-Tertiary Boundary (End of Mesozoic): • Main reason was the disruption of climate.The impact would have produced a dust cloud in the upper atmosphere that lasted for an extended period of time. This shielded Earth from solar energy and reduced global temperatures. Without sunlight, plants would die and animals would then starve. This disrupted the entire food chain and caused it to collapse.

9. Cretaceous-Tertiary Boundary (End of Mesozoic): • Main reason was the disruption of climate.Two Main Points Provide Support: • A layer of Iridium-rich sediment is seen at numerous locations throughout the world whose age corresponds to the Cretaceous-Tertiary boundary (66 million years ago). • An impact crater found in Mexico is dated to be approximately 66 million years old which corresponds to the mass extinction. • The extinction of the dinosaur is perhaps the most significant, seeing that these animals dominated Earth prior to the mass extinction.

10. Example 1: What is the most likely reason to explain the extinction of dinosaurs? disease (C) global warming glaciation (D) meteorite impact Geologic evidence suggest two major mass extinctions happened in the past. Between which geologic periods (or at the end of which Geologic Era) did these mass extinctions occur? 1) Geologic Time: _________________________________________ 2) Geologic Time: _________________________________________

11. Example 2: Explain how a past event, such as a meteorite impact, could cause a mass extinction on Earth today.

12. Example 2: Explain how a past event, such as a meteorite impact, could causea mass extinction on Earth today. Scientists believe that about 66 million years ago, a large meteorite collided with the Earth and is believed to have created a mass extinction event. The collision caused huge amounts of dust and materials to be ejected into the atmosphere. This blocked sunlight from reaching Earth which in turn caused a quick and drastic change in the climate. Plants and animals would not be able to adapt to the climatic change. As a result plants would die which in turn would cause the food chain to collapse resulting in a loss of many plant and animal species. This type of event could happen again in the Earths future. As we know, events which occurred in the past are similar to events today. This idea called uniformitarianism suggests that a mass extinction could happen again in our future.

13. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Questions: A mass extinction of trilobites occurred at the end of which geologic time span? (A) Cenozoic (C) Paleozoic(B) Mesozoic (D) Proterozoic The extinction of dinosaurs marked the end of which era? (A) Archean (C) Cenozoic (B) Mesozoic (D) Paleozoic

14. Solutions . . . Questions: A mass extinction of trilobites occurred at the end of which geologic time span? (A) Cenozoic (C) Paleozoic(B) Mesozoic (D) Proterozoic The extinction of dinosaurs marked the end of which era? (A) Archean (C) Cenozoic (B) Mesozoic (D) Paleozoic

15. Summary . . . Overview of Points covered: • Their was two major mass extinctions in the past: • End of the Paleozoic (Permian – Triassic Boundary) • Cause: Plate Tectonics • 2. End of the Mesozoic (Cretaceous – Tertiary Boundary) • Cause: Meteorite impact