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(Brief notes start here)
| Layer Name | Depth (km) | State | Composition | Density |
|
| Crust (Continental) | 55 (25-90) | solid (rigid) | "granite" | 2.7 | <1000 |
| Crust (Oceanic) | 10 (5-10) | solid (rigid) | basalt | 3.0 | <1500 |
| Mantle | to 2900 | solid (ductile) | Mg, Fe silicates | 4.5 | 1500-3000 |
| Core, Outer | 2900-5300 | liquid | Fe, Ni metal | 11.5 | 4000 |
| Core, Inner | 5300-6370 | solid | Fe, Ni metal | 13.0 | 5000 |
| Layer | Depth (km) | Rheology |
| Lithosphere | 150 (continents), 70 (oceans) | rigid, elastic |
| Asthensophere | bottom of lithosphere to ~250 | ductile, plastic |
"Big Bang"
Earth and Solar System
Origin of Oceans and Atmosphere
Oceans
Geologic Time Scale: based on record in rocks of "events"
(mountain building, fossil evolution); radioactive dating gave
"absolute" ages (in years).
Important events:
Origin of Earth: 4,600 m.y.
Appearance of "oceans": ~4,400 m.y.
Oldest preserved rock on continents: 4,200 m.y.
First bacteria: >3,800 m.y.
Photosynthesizing algae appear: 3,500 to 2,500 m.y.
O2 in the atm.: ~2,000 m.y.
Multicellular organisms: ~600 m.y.
First "hominids": ~4 m.y.
(Detailed notes begin here)
"Big Bang:" We know that the galaxies of the universe are rushing apart, i.e., the universe is expanding, and thus, the "birth" of the universe is assumed to have started with a dense, hot "exploding" moment. During expansion, the matter of the Universe "segregates" into lumps to form galaxies and their stars. The region between stars and galaxies contains gas and dust.
Earth and Solar System: The most widely accepted theory involves the following stages of development:
(1) Gravitational collapse of a rotating mass of interstellar
gas
(mostly H and He) and dust beginning about 5 billion years (b.y.)
ago.
(2) Formation of flat, rotating disk with matter concentrated into central "protosun" -- heating by compression and nuclear reactions in interior
(3) In the enveloping disk of gas and dust, cooling allowed
solids to condense and accrete into larger and larger bodies:
dust -->"pebbles"--> asteroid-sized bodies = "planetismals",
parents of meteorites ---> planets
The origin of the Earth, other planets, and meteorites is dated at 4.6 b.y. = 4600 m.y. (million years)
The Earth and other planets continued to be bombarded intensely by planetismals and comets to about 4400 m.y. ago; impacts continue to occur. This early, intense heating of Earth (impacts, compression, radioactive decay) lead to (a) violent volcanic activity and (b) segregation of interior into silicate mantle and metallic core.
Various lines of evidence indicate that the interior of Earth consists of three concentric shells: core, mantle, and crust. The following table lists the important physical and chemical properties of those internal shells
| Layer Name |
Depth (km) |
State | Composition | Density (g/cc) |
|
| Crust (Continental) | 55 (25-90) | solid (rigid) | "granite" | 2.7 | <1000 |
| Crust (Oceanic) | 10 (5-10) | solid (rigid) | basalt | 3.0 | <1500 |
| Mantle | to 2900 | solid (ductile) | Mg, Fe silicates | 4.5 | 1500-3000 |
| Core, Outer | 2900-5300 | l iquid | Fe, Ni metal | 11.5 | 4000 |
| Core, Inner | 5300-6370 | solid | Fe, Ni metal | 13.0 | 5000 |
The best evidence for this "model" of Earth's interior comes from the passage of seismic waves (earthquake-generated vibrations) through the Earth.
o Earthquakes are due to the sudden release of energy stored in the crust and mantle due to movement and deformation in those layers. When the amount of deformation becomes high, rocks are displaced violently, usually along a fault zone.
o Energy released by earthquakes is carried by different kinds of waves. The two most common are P-waves and S-waves.
Wave velocity changes and waves are bent (refracted) as they pass through different layers.
With the development of plate-tectonic theory, earth scientists realized that the outer portion of Earth (crust and upper mantle) behaves as a rigid lithosphere (broken into plates) underlain by a ductile (plastic) layer, the asthenosphere.
Internal Zones: lithosphere, asthenosphere
| Layer | Depth (km) | Rheology |
| Lithosphere |
150 beneath continents, 70 beneath ocenas |
rigid, elastic |
| Asthensophere | bottom of lithosphere to ~250 | ductile, plastic |
The composition of the atmosphere changed (evolved) as (a) reactive gases were oxidized and removed by reaction with surface rocks and (b) CO2 removed and O2 accumulated as life developed and evolved.
As earliest Earth surface cooled (first few 100 m.y.), water vapor condensed ("rained-out") to form the early ocean
Acidic gases (like HCl and H2SO4) were dissolved in this "rain" and reacted with surface silicate rocks to form (a) sediments and (b) dissolved products carried by rivers to the early ocean.
How have the oceans changed over their ~4,000 million years history? This is rather speculative, but our best estimates are:
(a) Salinity and area covered have remained about constant.
(b) Depth and volume probably increased over the first 2,000 million years of Earth history, as continental crust thickened and ocean basins became deeper.
Geologic time scale is like a "terrestrial calendar," in which geologic time is subdivided into units called Eons, Eras, Periods, etc. just like our annual calendar is divided into months, weeks, days, etc. The time scale was based initially on world-wide "events" recorded in rocks, such as fossil evolution (including mass extinctions) and the appearance of large mountain chains ("tectonic" events). Dating of rocks by radioactive methods gave ages in "years" to the "relative" geologic time scale.
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