Further Investigations: Change Over Time

Choose a mass extinction event from SF Table 7.2, and research its consequences.
Investigate an extinct animal species. Describe the physical features of this species, when it lived and how it is related to modern-day animals.
Research how geologists use index fossils to identify different geologic periods. What characteristics make a “good” index fossil? What are some of the index fossils associated with specific periods of time in Earth’s history?
Scientists have found fossilized marine coral in Tibet, a country in the Himalayan Mountains. Explain how marine organisms can appear high on continental mountains, far from the ocean.

**SF Table 7.2.** Table of mass extinction events by date and their possible causes
Date	Event Name	Level of Extinction	Possible Cause
0.01 mya	Quaternary	55% of large mammal genera	End of ice age, hunting by early humans
66 mya	Cretaceous-Paleogene	17% of families, including dinosaurs; 50% of genera; end of Age of Reptiles	Asteroid impact, volcanic eruption
205 mya	Triassic-Jurassic	23% of families; 48% of genera	Breakup of Pangaea, extensive volcanic eruptions
252 mya	Permian-Triassic	70% of all land species; 80-96% of marine species; end of Paleozoic era	Formation of Pangea leading to depletion of shallow seas, volcanic eruptions, glaciation
345 mya	Late Devonian	19% of families, 50% of genera	Glaciation, meteor impact
450 mya	Ordovician-Silurian	25% of families, 57% of genera	Glaciation, causing changes in sea level

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