Term
| The Hadean and Archean Eons comprise what percent of the Earths total history? |
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Definition
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Term
| What caused the formation of the moon? |
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Definition
| Collision of a proto-earth with a mars sized body. |
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Term
By what mechanism was the Earth created?
(Grouping together and condensing materials is called?) |
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Definition
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Term
| The transition from the Hadean to the Archean is distinguished by what? |
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Definition
| The cessation of meteorite bombardment |
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Term
| What was used to determine the age of the Earth? Why are these used? |
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Definition
| Zircons, used because of their resistance against weathering and metamorphism. |
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Term
| What processes brought about the first water on Earth? |
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Definition
| Volcanic outgassing and meteorite bombardment. |
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Term
| What evidence leads us to believe that the moon is younger than the Earth, that it was not formed at the same time? |
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Definition
| The moon is less dense, and its composition is similar to that of the Earths mantle, which suggests that the collision with the mars sized body happened when the earth had already began to separate into distinct layers. |
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Term
| The first protocontinents were caused by? |
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Definition
| Mantle convection, primordial heat |
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Term
| The first protocontinents were of what composition? |
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Definition
| Mafic. Similar to todays oceanic plates. |
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Term
| Why are some of the oldest rocks found in the middle of continents? (cratons) |
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Definition
| They are sheltered from destructive plate boundaries, continents are less dense than oceanic plates so they do not subduct, and felsic continental crust is more stable and resistant to erosion than oceanic crust. |
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Term
| What distinguishes a protocontinent from a continent? |
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Definition
| When the protocontinent reaches a similar size to the continents we know of today. |
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Term
| What are greenstone belts indicative of? |
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Definition
| The material in suture zones of protocontinents. |
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Term
| How are zircons used as evidence for protocontinents? |
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Definition
| Presence of light isotopes of oxygen. (Light oxygen is preferentially evaporated and then rained down onto the protocontinent to be locked away in zircons) |
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Term
| Describe the "primordial soup" hypothesis |
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Definition
| The necessary elements for life were contained in pools of water and were supplied with a source of energy (possibly lightning, which resulted in primitive life. |
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Term
| Why were mid ocean ridges a more likely place for the formation of life than the primordial soup theory? |
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Definition
| For life to first occur, there had to be no oxygen present. UV light passing through the early atmosphere created O2, so the deep anoxic enviro. of oceanic ridges provides a better suited place along with all necessary chemicals and an energy source. (also a puddle getting struck with lightning is pretty unlikely) |
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Term
| Why is the Earth layered? |
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Definition
| The dense materials sank to the middle and the light materials floated to the top. |
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Term
| Early lifeforms carried their genetic code on what molecule? |
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Definition
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Term
| What types of life were present in the Archean? |
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Definition
| Cyanobacteria(stromatolites) and bacteria. No eukaryotes, only prokaryote micro fossils have been found. |
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Term
| What caused a dramatic rise in the amount of free oxygen at the end of the Archean? |
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Definition
| The rise of stromatolite population. |
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Term
| What proof do we have that there were photosynthesizing organisms in the Archean? |
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Definition
| More light carbon isotopes (these are preferentially taken up by photosynthesizing organisms) |
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Term
| How were bacteria preserved? |
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Definition
| In chert and on the edges of cooling pillow basalts. |
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