Planet Earth - The Hadean Eon - Part Two

It started from approximately 4.5 billion years ago and ended approximately 3.8 billion years ago; the Hadean Eon named by the geologist, Preston Cloud , in 1972 was used to represent a time of bombardment by extra-terrestrial material, fire and possibly like a vision of hell. 

The examination of the moon's surface and by dating moon rock, it has helped to partition the Hadean Eon into further time periods:

Birth of the Moon - (4.527 billion years ago) an approximate date for when a bombardment hit the molten proto-planet Earth and thus created a satellite.

Pre-Nectarian - (3.92 billion years ago) an approximate date of the crust's formation of the moon.

Nectarian - (3.85 billion years ago) an approximate date of when the terrestrial bombardment started to recede.

Using locations in western Greenland, north western Canada and Western Australia, there are provisions of  evidence of Hadean sediments (Greenland) and zircon crystals (Australia and Canada). The crystals are estimated at 4 billion years old and the sediments to 3.8 billion years old. The latter rock has also evidence of banded iron beds with the potential for organic carbon and with that it suggests that photosynthetic life had already been established.

But as with all science and their associated theories and evidence; the suggested period of Hadean-like life as purported by Preston Cloud may be be different. During the time of bombardment, approximately 4.527 billion years ago, an impact into the partially molten planet may have formed the Earth's satellite, the moon. This dislodgement not only moves material but it also dislodges water molecules that have been trapped within the planet's rock structure and surface into the proto-atmosphere. This is due to the gravity of the planet being less strong due to the planet being 40% of its present size. This proto-atmosphere consisted of a heavy carbon-dioxide atmosphere laden with hydrogen and water vapour (a combination of hydrogen and oxygen). The raised atmospheric pressure, due to the presence of carbon dioxide led to collections of water be present on the planet's surface despite a suggested surface temperature of two hundred and thirty degree Centigrade (446 degrees Fahrenheit in old money).

The study of the zircon crystals in 2008 has shown that liquid water may have been present 4.4 billion years ago and they may also hold evidence of plate tectonic activity approximately 4.0 billion years ago. The action of subducting (sinking) plates traps both rock and carbon dioxide, so as the process carried on  it took more carbon dioxide out of the atmosphere. This reduced the greenhouse effect leading to a cooler surface temperature, the formation of rocks and even life. This, of course, at present is partially conjecture based on archaeo-geological (or palaeo-geological) evidence and next time, we enter the Archaean Eon.