gsc101 geography 101

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Minimum 6 pages of text (double-spaced, 1” margins, 12 pt font). Adding a few figures is fine, but they don’t count toward 6 page text requirement. Papers should describe the current state of knowledge of the subject matter, any important unresolved issues, and your suggestions for research directions that could help solve those issues. Suggested outline: 1. Introductory paragraph 2. Summary of current state of knowledge 3. What are the major unanswered questions? 4. How might one or more of these questions be addressed in future research? What are reasonable hypotheses or targets for further exploration or research? 5. Concluding summary 6. Citations – more than just Wikipedia!

The topic needs to be choosed in the following paragraph.

The Four Main Eons of Earth’s History • Hadean – 4.6 to ~4 billion years ago • Named for Greek god of underworld (unknown) • Archean – ~4 to 2.5 billion years ago • Name from Greek word for beginning/origin (of life) • Evolution of microbial life (some with photosynthesis) • But very little atmospheric O2 • Proterozoic – 2.5 billion to 542 million years ago • Name from Greek words for early animals/life • Rise in atmospheric O2 marked boundary from Archean • Rise of eukaryotes and first animals • Phanerozoic – 542 million year ago to present • Name from Greek words for visible animal/life • Boundary marked by explosion of eukaryotic evolution • Multiple extinction/evolution events

Geological Time Scale Eon Era Period Age (Ma)

What do we know about hadean eon? There are almost no Earth rocks known to be preserved from the Hadean Eon, so we know almost nothing about the Hadean Eon. We have even less direct evidence for Earth conditions during the Hadean Eon than we do for the formation of the solar system (e.g., evidence from meteorites). • The best direct evidence comes from special mineral grains (zircons) that formed during the Hadean Eon and were preserved in rocks that formed later (during the Archean Eon). These zircons show evidence for presence of water at surface of Earth during the Hadean Eon. • Much of what we think about the Hadean Eon is admittedly speculative, and there are contradictory models for explaining certain aspects of Hadean history. • Why do we care? During the Hadean Eon, Earth probably had extreme surface temperatures and was not conducive to life, but by the end of the Hadean Earth had acquired many of the characteristics required to support the development of life in the following Archean Eon – but little/no atmospheric O2 yet.

Zircon = zirconium silicate mineral (ZrSi04) very resistant to alteration or recrystallization. • Earth’s oldest known minerals are detrital zircons up to 4.4 Ga-old found in Australia. “Detrital” means the original rocks were eroded and the zircon grains redeposited elsewhere within younger sedimentary rocks. • Zircons were formed originally as mineral grains within igneous rocks that formed from magma that interacted with liquid water. • Uranium can easily substitute for Zr in the mineral structure, so the ages of zircons can be determined radiometrically by U-Pb dating. • Existence of zircons as old as 4.4 Ga suggests the existence of early continental fragments early in the Hadean Eon

• When and why did Earth’s atmosphere develop its O2 content? • Basic summary of evolution of life through present • K-Pg dinosaur extinction event

• Rock and fossil record defines geological time scale • What is life? How do we recognize signs of earliest life? • How did life arise on Earth? • Hydrothermal systems: Photosynthesis vs chemosynthesis • March 5: When and why did Earth’s atmosphere develop its O2 content?

• Development of Earth’s structure and earliest crust • Intro to Geological Time Scale: Hadean and Archean Eons origins of life on Earth

4 main eons

evolutionary tree of life on Earth

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