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Just to put things in context
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The Earth is roughly 4 billion years old, T-rex evolved roughly 4 billion years after the Earth was created, and humans evolved roughly 4 billion years after the Earth was created.
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Precambrian is made up of
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The Hadean, Archaean, and Proterozoic Eras, and ABIOGENESIS
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The HADEAN EON
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(4.5-4.0 billion years ago) is an unofficial eon.
The Hadean is characterized by high volcanic activity and heavy bombardment of the Earth by extraterrestrial bodies, such that the surface of the Earth is assumed to have been largely molten during this time. |
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The GIANT IMPACT HYPOTHESIS suggests that
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The moon was formed around this time by a collision between the Earth and another body approximately the size of Mars.
However, isotopic data calls this hypothesis into question. |
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There is an alternative hypothesis to the molten Earth scenario of the Hadean, called the
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COOL EARLY EARTH hypothesis.
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COOL EARLY EARTH hypothesis.
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Zircons are extremely tough minerals which can survive in environments which destroy or melt other rocks. Extremely old, pre-Archean zircons have been found in Australia, Canada, and Greenland. ISOTOPIC ANALYSIS of these mineral grains suggest that they were formed in a wet environment, implying the existence of liquid water during the Hadean Eon.
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LATE HEAVY BOMBARDMENT hypothesis
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That approximately 4 billion years ago the inner solar system was bombarded with asteroids.
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Was the Hadean generally hot or cool?
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Whether the Hadean was generally cool or hot is hard to say. When the Apollo astronauts brought back rock samples from the moon, it became apparent that most of them had been melted around 4 billion years ago.
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During the formation of the early solar system, _______ materials get blown off the inner planets by the solar wind. This includes the ______ which probably made up the Earth’s first atmosphere. Bombardment by asteroids would also have helped remove this gas. This is why.... ______________
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VOLATILE, hydrogen, the inner solar system planets are terrestrial and rocky, and the outer solar system planets are gas giants
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During the formation of the early solar system, _______ materials get blown off the inner planets by the solar wind. This includes the ______ which probably made up the Earth’s first atmosphere. Bombardment by asteroids would also have helped remove this gas. This is why.... ______________
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VOLATILE, hydrogen, the inner solar system planets are terrestrial and rocky, and the outer solar system planets are gas giants
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Where does the Earth’s atmosphere come from?
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Some gases, such as nitrogen and carbon dioxide were tied up in rocks, and not driven from the Earth. Volcanic activity released these gases to create Earth’s second atmosphere, composed mostly of these two gases.
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Some researchers have hypothesized that Earth’s water came from _____ and _____
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Asteroids and comets.
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This is a testable hypothesis because
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Materials from the same place usually have the same ISOTOPE RATIOS
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In this case....
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Earth seawater isotope ratios do not match those of comets which have been measured, but they DO match the ratios of chondritic meteorites which have been measured.
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By around _____ years ago, the ____________had ended, the Earth’s surface began to cool, and rocks began to form. This begins the ________
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3.8 billion, Late Heavy Bombardment, ARCHEAN EON, 3.8-2.5 billion years ago.
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