Thursday, December 01, 2011

Nature: newborn Earth's atmosphere close to ours

As soon as our planet was born together with the Solar System about 4.7 gigayears before Jesus Christ ;-), it entered the so-called Hadean eon. About 3.85 billion years ago, Hadean was superseded by Archean.

This is a rare photograph because during the Hadean eon, they didn't possess too many digital cameras. The Moon (if it is the Moon) seems large: our satellite was about 30% closer than it is today.

The name is derived from the Greek word "Hades" which means something like "underworld" or "socialism". Tom Vonk may tell us whether "Hades" is etymologically related to "had" which is a snake in Czech. ;-)

This terminology is meant to indicate that the world probably resembled the Hell. Well, this has always been a somewhat loaded term because you would imagine that the climate was hot. However, the young Sun actually boasted just 70% of the current output (according to the current solar models) so it should have been very cool over here. However, the data indicate that we had liquid water from the beginning. This mismatch in the most naive estimate of the temperature is known as the faint young Sun paradox.

The chemical composition of the atmosphere is yet another unknown. It could have been much less hellish than expected, too.

At least, this is the main claim of the following new paper in Nature,
The oxidation state of Hadean magmas and implications for early Earth’s atmosphere
written by Dustin Trail, E. Bruce Watson, and Nicholas D. Tailby. They made some redox-sensitive calibration of the oldest minerals and determined that the oxidation state of the magmas on Earth was close to ours.

Just to be on the same frequency: "redox" stands for "reduction and oxidation". Oxidation is an atom's loss of electrons (it plays the role of a less negative or more positive ion in the molecules than what it did before); reduction is the gain of electrons. For example, carbon \(C\) is neutral and it oxidizes to become \(C^{++}\) or \(C^{++++}\) in \(CO\) and \(CO_2\), respectively. Oxygen is consistently capable of coming in the \(O^{--}\) form so it is the primary element that is able to oxidize others (and the universal process is therefore named after oxygen).

Well, they looked at some chemical properties of the magmas and decided that there had to be much more oxygen in the atmosphere than previously thought. I am not able to verify their claims.

Previously, the newborn terrestrial atmosphere would be full of oxygen-poor compounds such as \(CH_4\), \(H_2\), \(H_2S\), \(NH_3\), and \(CO\). But if they're right, the atmosphere would have been dominated by friendly gases such as \(H_2O\), \(CO_2\), \(SO_2\), and \(N_2\). Well, \(SO_2\) is not too friendly but it is still very familiar to our noses, at least the noses of us who grew up in the socialist bloc.

Of course that I believe that only some very hardcore technical research may resolve such fascinating qualitative questions such as the question whether the newborn Earth was very different from the modern one or pretty similar to the present blue planet as we know it. On the other hand, it's fascinating to think about the question whether we could nevertheless try to find some legitimate "philosophical" or "quasi-religious" arguments why the answer should go in one way or the other, e.g. some anthropic arguments. (We surely do know that the Universe as a whole was cooling and changing in pretty monotonic ways from the beginning.) A simple example of such an assertion I can make is that it is surely easier for life to evolve and adapt if the atmosphere isn't changing "qualitatively".

At any rate, if the authors are right, the Earth will look even more "self-regulating" in the long run than what we were believing yesterday.

See also a press release.

1 comment:

  1. This is nuts, there was nothing except life coming along about a billion years after the earth formed that could possibly have converted a reducing atmosphere to an oxidizing one.

    "Methane greenhouses" invented by mescaline-stupefied hippie astronomers like Carl Sagan to explain the presence of ocean water in the presence of a 20-30% weaker Sun are even more nuts.

    Fossils of what must have been Archean protozoa clearly show that heating came from the bottom up and not from the top down; evidently the heat was geothermal of origin, even though the Earth had cooled sufficiently over the first 100 - 500 million years to allow water to freeze, the continents had not yet formed and plate tectonics must have accounted for most of the geothermal heat (and not as yet decayed isotopes of uranium, thorium, and potassium accounting for the other fraction).

    This greenhouse was invented to promote the idea that if a greenhouse "happened once it could happen again"

    Four billion, six hundred of million years of Earthly history need to be revised by the Communist Party to justify the need for carbon taxes and solar panels.

    Jesus, the Bolsheviks only needed to revise a couple thousand years of history to justify themselves.