Geology Ch. 13
Terms
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- When did the major mass extinction events occur?
-
The most intense mass extinction event is the boundary between the
Permian Period and the Triassic Period. It also marks the boundary
between the Paleozoic Era and the Mesozoic Era. 245 Ma
The best known mass extinction event is the boundary between the
Cretaceous Period and the Tertiary Period, which is also the boundary
between the Mesozoic and Cenozoic Eras. 65 ±0.4 Ma -
Permian Extinction (245 Ma)
Results -
Many of the marine
species became extinct. Swimming reptiles became important and
hexacorals became the dominant reef builders. Turtles and flying
reptiles started. Cyads (a type of primitive plant) diversified. -
Cretaceous Extinction (65 Ma)
Results -
Dinosaurs
out. Grasses + mammals in. -
Permian Extinction (245 Ma)
Causes & Evidence -
It may be a large volcanic
event in Siberia. Or it could be a meteorite impact whose crater has disappeared. Remember, 70% of the earth's surface is oceanic crust. Because it is subducted, we have no oceanic crust older than about 190 MY now. So, if a Permian-Triassic meteorite that hit in the oceans was
the cause, its crater has vanished. The problem is, there seems to be no other evidence of such an impact in continental sediments like there was for the K-T (i.e., no spherules; no ash layer; no Iridium-rich
clay). -
Cretaceous Extinction (65 Ma)
Causes & Evidence -
Meteorite collision in Yucatan peninsula
1. Clay layer rich in Iridium distributed
globally
2. Carbonized ash in the same time layer (evidence of forest
fires).
3. Glass spherules in the sediments at the Cretaceous-Tertiary
boundary: these are the products of the melting that took place when the meteorite hit.
4. The crater in the Yucatan.
5. Sedimentary evidence for a huge tsunami at the same time - What are cratons?
- long lived blocks of durable continental crust, commonly found in stable interior of continent
- What are platforms?
- phanerozoic strata bury most of the Precambrian rocks, forming platforms
- When did supercontinents form?
-
Rodinia- 1 Ga
Pannotia- 800-600 Ma
Pangaea- 300 Ma - How has oxygen content of the atmosphere changed over time?
- Oxygen has increased as life forms have increased, in term allowed more complex organism to develop. Had biggest during change Proterozoic.
- How has the amount of continental crust changed over time?
-
>80% of the crust was built by the end of the
Archean Eon; nearly 100% by mid-Proterozoic Eon and later