Scientists have modeled
the chemical composition was found in the limestone age of 2.7 billion years
micrometeorites. The obtained results indicate very high (more than 70
percent by volume) carbon dioxide content in the atmosphere of the time. Gas
shell with these properties can explain the high temperature of the Earth in
the late Archean, despite the fact that the Sun at that time should be significantly dimmer, write the authors in the journal Science Advances.
The composition of Earth’s atmosphere
have undergone considerable changes over the life of the planet. In
the early periods in the gas shell were virtually no required for
breathing oxygen, since this substance is chemically very active.
One of the key events
in the evolution of the Earth is oxygen catastrophe, which occurred about 2.45
a billion years ago. At this time, the air began to appear pure oxygen
what associated with the activities of photosynthetic organisms. This stage is so
strongly affected the biosphere and Geology of earth’s crust that he shared
ancient period the history of the planet, the archaea, from subsequent history.
The concentration of carbon dioxide
gas in the Archean is known bad. There are separate estimates based on different
methods which give values between 3 × 10-3 to 0.75 bar, that is different
about three orders of magnitude. The composition of the ancient atmosphere are important in the context of
climate of the early Earth and the conditions of existence of primary life. On the one hand,
so long gone the Sun was 20-30 percent darker, but on the planet clearly present liquid water, and according to some it
typical temperature reached 70 degrees Celsius.
American scientists when
the participation of Owen Lehmer (Lehmer Owen) from the University of Washington evaluated
early carbon dioxide by modeling the oxidation of micrometeorites,
preserved in the limestone rocks, the age of 2.7 billion years. In the previous
it has been shown that the observed composition of bodies can be explained by the interaction
with atmosphere with modern fractions of oxygen, which does not match the current
views. According to the results of a new study, in the case of carbon dioxide
gas will need a content of not less than 70 percent.
When Nickel-iron micrometeorites
entering the atmosphere at high speed, they can melt due to
heat from friction. In the case of a liquid state such bodies come into
active reaction with oxygen or carbon dioxide, oxidized to wustiteor
magnetite. While such bodies may solidify before colliding with
surface and in the oxidized state, have chemically inert and stored
throughout geological time.
Scientists have created a numerical
model and spent 15 thousands of simulations of the fall of micrometeorites through the atmosphere of
carbon dioxide and nitrogen with the pressure of modern. Calculations
repeated for the case of the atmosphere with the addition of pure oxygen with a concentration of not
more of interest which may arise as a result of photodissociation of carbon dioxide
gas in the upper atmosphere.
In the end, the authors come to
the conclusion that the explanation of the available data on the oxidation of micrometeorites
need age need the atmosphere with carbon dioxide content approximately
64 percent. The estimate is almost independent of the presence of impurities
oxygen and the total pressure, but its error is very high — two standard deviation range from
-58 to +36, that is, range from 6 to 100 percent. Scientists say that such a low accuracy in the first place
associated with a large scatter of the only two at the moment, quality
measurements of oxidation of micrometeorites — 0,555 and 0.003. At the same time, for
the receipt is almost completely oxidized body, regardless of the settings
its trajectory requires at least 70 percent of the carbon dioxide in the atmosphere (against
0.04 percent modern).
Climate models with
such high levels of carbon dioxide predict global average
the temperature of the Earth in the late Archean at 30 degrees centigrade (lower if the pressure was less modern). The researchers also
note that there are many iron micrometeorites that fell in the next EON
— the Proterozoic. If the measure of the degree of oxidation of a substance in them, then tested
method to assess the concentration of carbon dioxide, and for other
ages, at least until the oxygen content at low altitudes was
Previously, scientists found evidence that atmospheric pressure on the ancient Earth was two times lower than modern. There is also limited evidence that oxygen was present in the atmosphere, before the oxygen catastrophe.