Thursday, July 30, 2009

The Planet Hunters - Extreme Life - Eating Rocks - The debate part deux

Eagle averro/true masked wabbit

In the last debate with eagle averro and myself we were debating about micro organism that can feed on rocks (coming up article, micro organisms that feed on iron). In that discussion we both stumbled on to another dilemma where we stand on the opposite side of the spectrum and undoubtedly will head into another fierce discussion where feathers and fur will be flying; whether or not our earth began in the Hadean Eon as some scientists claim as findings had suggested, or whether our earth was covered entirely in water, relying on the crystal rocks recently found in Australia dating as far back where the chemical make up of the Jack Hills crystals suggests that they formed in the presence of liquid water, likely even an ocean. These crystals provide evidence that even the very early Earth was cooler and wetter than scientists used to think. A gentler Hadean could have permitted life to evolve far earlier in the planet’s history than scientists originally supposed.

In the absence of Hadean rocks, scientists have relied on indirect evidence of what went on for 500 million years after the formation of the Earth about 4.57 billion years ago. Lunar observations and astronomical models of solar system formation paint a picture of a violent Earth, bombarded with meteors, covered with an ocean of magma, and boiling with volcanic activity. This fiery, Hades-like image gave rise to the period’s name.

4.6 to 3.8 billion years ago The Hadean includes the first 800 million years of Earth's history - the time of the formation of the planet from a presumably molten mass. The oldest dated rocks found so far are from Canada and are dated at 3.96 billion years old, the end of the Hadean. Any older rocks either are deeply buried and yet to be found or have been remelted and recycled. Meteorites and moon rocks date from this ancient time when the Earth's crust was forming and was continually bombarded by meteorites and comets.

During Hadean time, the Earth and Solar System formed by coagulation and gravitational contraction from a large cloud of gas and dust around the sun, called an accretion disc. The sun formed the nucleus, shrinking in on itself by gravitational compaction until it reached a stage where it ignited with nuclear fusion and give off light and heat. The surrounding particles within this cloud coalesced into planetisimals which then aggregated to form microplanets (rather like modern asteroids).

The energy of the collisions between the larger microplanets, as well as interior radioactive and gravitational heating, generated a huge amount of heat, and the Earth and other planets would have been initially molten. The Earth and Moon formed rather late in this process, from a collision between two large bodies -- a mars-sized planetoid and a slightly larger body.

During this period the heavier molten iron sank to the down to become the core, while the lighter rock rose to the surface. The lightest of all became the crust as a sort of "scum" on the surface. There was also an outgassing of volatile molecules such as water, methane, ammonia, hydrogen, nitrogen, and carbon dioxide. An initial steam atmosphere formed of water from comets and hydrated minerals. Rain fell to form a proto-ocean 4.3 to 4.4 billion years ago. All terrestrial planets had a similar process in their early histories.

Once most of the planetisimals were gone the planetary bombardment stopped, and a stable rocky crust was able to formed on the Earth. This is the age of the oldest rocks on earth and also of moon rocks. Atmospheric water condensed into oceans and proto-life formed in the soup of primordial organic molecules, either in the early oceans or in clay or rocks within the crust itself.

Foot note: While it is true that at times eagle averro and I get into a furious debate of whose theory holds better scientific logics, to the point where I worry if I’ll give him a heart attack I want to reassure everyone our fierce debates are exactly that, fierce debates with a respect towards each other’s theories and we both know when to call it a draw until further scientific facts come to the surface or just simply walk away from the debate before we scratch either’s eyes out. And so the debate continues …

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