Wednesday, February 22, 2012

First Civilization Part 1 Chapter 3

 

4450 Ma: 100 million years after the Moon formed, the first lunar crust, formed of lunar anorthosite, differentiated from lower magmas. The earliest Earth crust probably forms similarly out of similar material. On Earth the pluvial period starts, in which the Earth's crust cools enough to allow water accumulate in pools and streams.

pluvial earth

Pluvial Earth

4400 Ma: First known mineral, found at Jack Hills in Western Australia. Detrital zircons show presence of a solid crust and water.

oldest zicron2

Oldest Zircon form Jack Hills area western Australia

This is Latest possible date for a secondary atmosphere to form, produced by the Earth's crust outgassing, reinforced by water and possibly organic molecules delivered by comet impacts and carbonaceous chondrites (including type CI shown to be high in a number of amino acids and polycyclic aromatic hydrocarbons.

allen3CC

A Carbonaceous Chondrite Comet

late-heavy-bombardment

Late Heavy Bombardment

 

During the Archean Eon the Late Heavy Bombardment occurred (approximately 4100 Ma to 3800 Ma) during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus and Mars as well was produced by comets and asteroids. This was caused  by the planetary migration of Neptune into the Kuiper belt as a result of orbital resonances between Jupiter. Gravitational disruption from the outer planets' migration would have sent large numbers of asteroids into the inner Solar System, severely depleting the original belt until it reached today's extremely low mass. This event is what may have triggered the Late Heavy Bombardment. This period of heavy bombardment lasted several hundred million years and is evident in the cratering still visible on geologically nearly dead bodies of the inner Solar System such as the Moon and Mercury.

moon early

The Early Moon

The oldest known evidence for life on Earth dates to 3.8 billion years ago—almost immediately after the end of the Late Heavy Bombardment.  Mars's two small moons, Deimos and Phobos both thought to be originally asteroids, are believed to have been captured by this time.

marsmoon

Mars and its two Moons

The first signs of life were showing up on Mars too.

Ordovician_Land_Scene

The Mid Noachian or Early Theakian Period on Mars

The Earth of the early Archean Eon (3,800-2,500 Ma) may have had a different tectonic style. During this time, the Earth's crust cooled enough that rocks and continental plates began to form. Some scientists think because the Earth was hotter, that plate tectonic activity was more vigorous than it is today. In contrast to the Proterozoic, Archean rocks are often heavily metamorphized deep-water sediments, such as graywackes, mudstones, volcanic sediments and banded iron formations. Greenstone belts are typical Archean formations, consisting of alternating high- and low-grade metamorphic rocks. The high-grade rocks were derived from volcanic island arcs, while the low-grade metamorphic rocks represent deep-sea sediments eroded from the neighboring island arcs and deposited in a forearc basin. In short, greenstone belts represent sutured proto-continents. About 3.5 billion years ago, the magnetic fields of Earth and Mars were formed.

earths_field_

The Magnetic Field of Earth

original Mars Magnetosphere

Mars Early Magnetosphere

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