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What is the oldest unit on the Geologic Time Scale? (hint: Eon)
The Archean Eon; 4.6 billion years ago
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The Precambrian Period is comprised of what 2 Eons?
- 1.) Archean Eon
- 2.) Proterozoic
- spans 87% of the Geologic Time Scale
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The oldest rocks that have been dated are meteorites
4.6 billion years old
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The oldest dates of Earth rocks are detrital zircon grains in a sandstone in western Australia
4.4 billion years old
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Earth’s oldest know crustal rocks, found in Canada
4.4 billion years old
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Earth > Solar System > Milky Way galaxy > the Universe
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How old is the Universe?
13.7 billion years old; big explosion (Big Bang)
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Solar Nebula Hypothesis (how solar system formed):
Solar system distilled from a rotating cloud of dust, particles, and gases (called solar nebula)
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(Solar Nebula Hypothesis) Heavier material concentrated towards the center. created terrestrial planets such as:
Mercury, Venus, Earth, Mars
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(Solar Nebula Hypothesis) lighter material at the periphery. Jovian plants that include:
Jupiter, Saturn, Uranus, Neptune
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Chunks of rock from the Solar System that reach Earth's surface; include fragments of asteroids, moon rock, planets
Meteorites
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Earth's internal layered structure is composed of 3 actions:
- 1.) Accretion
- 2.) Shrinking due to gravitational compression
- 3.) Differentiation
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Homogeneous conglomeration of space debris occurs during:
Accretion
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Raises internal temp. to melt irons, nickel
Shrinking due to gravitational compression
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Gravitational seperation, heavier materials toward center (forming core), light materials float out to form mantle/crust
Differentiation
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The Archean Crust
magma cooled to form oceanic crust (komatiites-basalt); partial melting of basalt at subduction zone created first continental (i.e. granitic) crust
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Earth has 2 types of crust today:
- 1.) Dense, mafic (Mg, Fe) oceanic crust dominated by basalt.
- 2.) Less dense, sialic (Si, Al) continental crust dominated by granite
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Today we are adapted with air that has 21% oxygen
Earth's first atmosphere lacked free oxygen. Evidence: lack of oxidized iron in the oldest sedimentary rocks
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Early Ocean: formation of hydrosphere in 2 steps:
- 1.) Volcanic outgassing released water-vapor into the atmosphere
- 2.) Water-vapor condensed and fell as rain to form seas
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Having outgassed all the water early in history, Earth has been recycling it ever since via the _____ cycle
Hydrologic cycle (evaporation, condensation, rain, etc).
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Free oxygen started to appear after 3.7 billion years ago when photosynthetic prokaryotes appeared
Oxygen was abundant in the atmosphere around 2.5 billion years ago– when photosynthetic eukaryotes evolved
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The earliest evidence of life occurs in 3.5 billion year old sedimentary rocks
Stromatolite, an organo-sedimentary structure; Microscopic cells of prokaryotes, photosynthetic cyanobacteria, or blue-green algae
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Life may have also originated at midoceanic ridges because:
Nutrient-rich, heated water supports chemosynthetic bacteria
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The earliest organisms that developed in the atmosphere which lacked oxygen:
anaerobic prokaryotes. unlike photosynthesis, energy is produced by chemosynthesis
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Later evolved photosynthetic prokaryotes
use photosysthesis to produce energy and oxygen as byproduct
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Finally evolved eukaryotic cell, which could cope with oxygen in the atmosphere
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