--------------------- #1506 - Geological History of the Earth
- The planet Earth was formed 4,600 million years ago ( MYA) along with the nine other planets and a whole lot of other debris. ( See Review #1507 for the astronomical geological history of the Solar System.)
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- The oldest rocks found to date are the debris from the formation of the Solar System that have arrived as meteorites. These oldest rocks are called “ Chondrites” and they have been dated at 4,568 MYA.
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- Chondrites are stony meteors containing Chondrules, and Chondrules are small spheres of olivine or pyroxene. Olivine being a mineral found in igneous rocks containing the elements consisting of magnesium iron silicates. Pryoxene is a very similar group of minerals that are silicates of magnesium, iron, calcium and other elements.
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- Minerals are molecules and compounds of the elements which were formed in supernovae explosions. We know our Solar System accretion disks was composed of debris from 2nd or 3rd or 4th generation stars that died as supernovae. The larger the star the shorter its lifetime and the sooner supernova occurs. We know that because our Solar System is rich in the heavier elements it came from the generational stars.
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- In the beginning it was just the elements hydrogen and helium. The supernovae created the heavier elements. Then these elements began growing into molecules and compounds called minerals. A small number of elements in the beginning have grown to over 4,500 minerals found today. And, the list grows at the rate of about 12 new minerals per year being discovered.
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- 4,550 MYA: There were about 150 minerals on the planet. Minerals are inorganic substances having definite chemical composition and often a definite crystalline structure.
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- 4,500 MYA: The Moon was formed. It was believed to be created by the Earth’s crust being splashed into orbit after being hit by a meteor or a sub-planet, about the size of Mars. (footnote 2).
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- 4,400 MYA: The second oldest rocks to be found were zircons. Zircons are zirconium silicate minerals, ZrSiO4, having a tetragonal shaped crystalline structure. Zircon crystals are hard enough to resist erosion. They have a high melting point and can withstand most chemical attacks.
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- 4,200 MYA: Most of Earth’s atmospheric oxygen was in the form of water vapor.
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- 4,000 MYA: The list of minerals had grown to about 350 different minerals. The Earth’s crust was forming new compounds and molecules out of the elements churned in the caldron of volcanoes and tectonic lava flows.
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- 3,900 MYA: Earth and the Moon experienced very heavy meteor bombardments. (footnote 1).
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- 3,800 MYA: Earth’s surface solidifies, liquid water first appears, and the oceans formed.
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- 3,700 MYA: Coarse-grained igneous rocks formed called Granites. These Granites were composed of feldspars, and quartz with some mica, hornblende, and augite. feldspars are a group of minerals composed of aluminosilicates of potassium, sodium, and calcium. Quartz is silicon dioxide, SiO2. It is the chief constituent of sand. By now 550 minerals existed on the Earth.
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- 3,600 MYA: The planet’s first super continent formed.
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- 3,500 MYA: The planet’s first life arrived in the form of single-celled cyanobacteria .
Cyanobacteria began the first photosynthesis. ( Spring Lake has had an algae bloom this summer. Green algae has filled the lake. Mats of algae formed on the surface and blue-green moss-like colors formed on the mats. This was cyanobacteria that is toxic if ingested. I had to be careful to keep my dog out of the water. We walk around the lake every day. Dogs lick their fur that gets wet and can get poisoned.) (See footnote 1)
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- 2,500 MYA: The Earth has now created 1,500 different minerals.
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- 2,400 MYA: The algae and photosynthesis in the oceans have created oxygen in the atmosphere. ( See footnote 1).
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- 1,500 MYA: Oxygen has reached the concentration of 10% of the gas in the atmosphere.
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- 1,000 MYA: The super continent “ Rodina” has formed.
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- 310 MYA: The oxygen content in the atmosphere reaches 30%.
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- 250 MYA: The oxygen content has dropped to 12%.
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- 200 MYA: The Pacific Ocean forms.
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- 180 MYA: North America separates from Africa.
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- 110 MYA: The Atlantic Ocean forms.
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- 60 MYA: The Rocky Mountains form.
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- 0 MYA: Today, there are over 4,500 minerals in the Earth’s crust and the atmosphere has 21 % oxygen.
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- (1) 2.400 MYA: was the greatest climate change Earth has ever experienced. the primordial methane-rich atmosphere changed to an oxygen content level that we can still breath today. This change occurred because primitive , single-celled cyanobacteria began the process of photosynthesis to be alive.
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- The bacteria took in carbon dioxide and warm sunlight to grow while exhaling oxygen into the atmosphere. The rocks in the Earth took on the oxygen and “ rust” until there were no more unoxidized metals left. After that there was a runaway build up of oxygen in the atmosphere.
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- (2) The six Apollo missions to the Moon brought back 842 pounds of lunar rocks. All the rocks were dated to 4,000 MYA to 3,850 MYA. This is hundreds of millions of years after the Moon was formed. The conclusion: The Earth and the Moon were bombarded with these rocks for a period of 100 million years. The bombardment almost completely remade the surface of the Moon by 3,850 MYA.
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- (3) What caused this immense meteor bombardment?
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- There are several theories still under study. A likely scenario has the outer planets orbiting nearer to each other and nearer to the Sun when the Solar System first formed. Originally the giant planets were 5 to 17 astronomical units from the Sun. ( The Earth is 1 AU). The asteroid belt was 35 AU distant. After a few hundred million years Jupiter and Saturn passed through orbits that had 2:1 resonance. Jupiter made 2 revolutions around the Sun for every 1 revolution Saturn made. The combined gravitational effects of these resonances caused Uranus and Neptune to pass through the asteroid belt scattering the small bodies everywhere. These meteors entered the inner Solar System and created the bombardments on the Earth, Moon , and inner planets.
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707-536-3272, Tuesday, October 30, 2012
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