1. When does the Proterozoic Eon start and when does it end? 2. What is a craton
ID: 288507 • Letter: 1
Question
1. When does the Proterozoic Eon start and when does it end?
2. What is a craton?
3. How did cratons grow to their present size? That is, how did they grow in AREA? How did they get thicker?
4. Where did the water come from to fill today's ocean basins?
5. What are the two most abundant gases in today's atmosphere? Give a percentage of the atmosphere for each.
6. How does this compare to the gases coming out of volcanoes?
7. If volcanoes were the main source of the gases found in our atmosphere today, and if Proterozoic volcanoes released similar gases (and we think they did), then what happened to the vast amounts of carbon dioxide gas? Explain using two steps.
8. Why is the process of oxidation important for understanding how our atmosphere evolved? What minerals were NOT oxidized and what does that tell us, and what mineral WAS oxidized and when and how did this happen?
9. What would Earth be like today if the excess carbon dioxide had not been removed from the atmosphere in Precambrian time?
Explanation / Answer
1. The Proterozoic Eon began 2,500 million years ago and ended 541 (+/- 1) million years ago.
2. Cratons are pieces of continents that have been stable for a over a billion years. They are a coherent domain of Earth's continental crust that have attained and maintained long-term stability, they have undergone little internal deformation, except near its margins due to interaction with neighbouring terranes.
3. The Cratons were small during the Precambarian period and were very mobile and occasionally collided. But when crustal movement slowed considerable around 2 billion years ago, then pieces of granitic crust tended to stick together after collosion rather than breaking away. The North America and other continents of 2 billion years accumlated additional crust at the edges of their cratons and thus making them thicker and larger.
4. Millions of years ago there were no oceans on the planet. The surface of the Earth was so hot that water simply boiled away. But volcanoes poured huge amounts of steam into the atmosphere and as the Earth cooled down the steam turned to water vapor that condensed as droplets and began to fall as rain. This downpour lasted for many thousands of years filling great hollows in the land and thus forming the world's first seas. Thus filling up the oceans.
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