Primeval 4 – Archean Eon

 

Since the Late Heavy Bombardment life has thrived on the Earth, first during the Archean Eon, and then throughout the Proterozoic and Phanerozoic Eons that followed. Life during the Archean Eon was quite different from the eons that followed. At the time, the atmosphere was thick, dark, and contained very little oxygen, meaning that the life that thrived in it was anaerobic.(1)Alexander A. Pavlov et al. (May 2000) “Greenhouse warming by CH4 in the atmosphere of early Earth” Journal of Geophysical Research, Volume 105, Number E5, Pages 11981–11990 Anaerobic life forms do not require oxygen to survive. This eon lasted until about 2.3 billion years ago, when the Great Oxidization massively altered the atmosphere. This event was a sudden rise in the free oxygen in the atmosphere, which is itself, another mystery.

Archean Eon

Archean Eon

The Great Oxidization, also called the Oxygen Catastrophe, is generally related end of the Faint Young Sun Paradox. In 1972, astronomers Carl Sagan and George Mullen first raised the issue of the Faint Young Sun Paradox, when they observed the apparent contradiction between observations of liquid water early in Earth’s history and the astrophysical expectation that the Sun’s output would be only 70 percent as intense during that epoch as it is during the modern epoch.(2)Carl Sagan and George Mullen (1972) “Earth and Mars: Evolution of Atmospheres and Surface Temperatures” Science, Volume 177, Number 4043, Pages 52–56 In the standard solar model, stars like the Sun gradually brighten over their main sequence lifetime.(3)D. O. Gough (1981) “Solar Interior Structure and Luminosity Variations” Solar Physics, Volume 74, Number 1, Pages 21–34 The predicted solar luminosity 4 billion years ago, should have resulted in any liquid water on the surface of the Earth being frozen solid. Nevertheless the geological record shows a continually warm surface throughout Earth’s early existence, with the exception of a cold phase, the Huronian glaciation, about 2.4 to 2.1 billion years ago.

The Huronian glaciation is generally believed to have been caused by the Great Oxidization, as the carbon-dioxide in the atmosphere was converted into oxygen and greenhouse effects of the carbon-dioxide were lost. Attempts to explain the early Earth’s warm surface have looked at increased levels of greenhouse gases, however an analysis of nitrogen and argon isotopes in fluid inclusions trapped in 3.5 to 3.0 billion year old hydrothermal quartz concluded that dinitrogen did not play a significant role in heating the atmosphere of the ancient Earth and that the Archean Eon partial pressure of carbon-dioxide was probably lower than 0.7 bar,(4)B. Marty et al. (2013) “Nitrogen Isotopic Composition and Density of the Archean Atmosphere” Science, Volume 342, Number 6154, Page 101 meaning it did not play much of a role either.

Another attempt to explain the warm young Earth suggested it could have been caused by an increased geothermal release of decay heat. The heat emitted from the decay of the isotopes potassium-40, uranium-235 and uranium-238 was considerably greater than it is today.(5)R. Arevalo Jr. et al. (2009) “The K/U ratio of the silicate Earth: Insights into mantle composition, structure and thermal evolution” Earth and Planetary Science Letters, Volume 278, Number 3, Pages 361–369 This theory suggests that naturally occurring nuclear reactors could have provided warmth to the world, however there is no evidence of excessive radiation in the young Earth as the theory predicates.

Greater tidal heating caused by the Moon being closer to the Earth would have also been present, however the Earth maintaining a relatively warm state for over a billion years when it should have been frozen is not yet explained by all of these explanations combined. The planet seems to have been artificially maintained at a warm temperature for a very long time. If this was caused by an intelligent civilization, then they must have been fundamentally different than us, as the atmosphere at the time would have only supported anaerobic lifeforms.

anaerobicorganism

Loricifera – Multi-Cellular Anaerobic Lifeforms

While multi-cellular anaerobic lifeforms do exist on the Earth,(6)Gretchen Vogel (2010) “ScienceShot: Animals That Live Without Oxygen” Science Magazine they are very rare in our oxygen-rich biosphere, so we don’t know how they might have evolved in the 1.5 billion year long Archean Eon. Most rocks we have from the eon are heavily altered by billions of years of heat, pressure and deformation, and it is unlikely that any actual fossils could have survived to the present. Archean rocks are often heavily metamorphized deep-water sediments, such as graywackes, mudstones, volcanic sediments, and banded iron formations. Carbonate rocks are rare, indicating that the oceans were more acidic due to dissolved carbon-dioxide than during the later Proterozoic Eon.(7)John D. Cooper et al. (1986) A Trip Through Time: Principles of Historical Geology Page 180

References   [ + ]

1. Alexander A. Pavlov et al. (May 2000) “Greenhouse warming by CH4 in the atmosphere of early Earth” Journal of Geophysical Research, Volume 105, Number E5, Pages 11981–11990
2. Carl Sagan and George Mullen (1972) “Earth and Mars: Evolution of Atmospheres and Surface Temperatures” Science, Volume 177, Number 4043, Pages 52–56
3. D. O. Gough (1981) “Solar Interior Structure and Luminosity Variations” Solar Physics, Volume 74, Number 1, Pages 21–34
4. B. Marty et al. (2013) “Nitrogen Isotopic Composition and Density of the Archean Atmosphere” Science, Volume 342, Number 6154, Page 101
5. R. Arevalo Jr. et al. (2009) “The K/U ratio of the silicate Earth: Insights into mantle composition, structure and thermal evolution” Earth and Planetary Science Letters, Volume 278, Number 3, Pages 361–369
6. Gretchen Vogel (2010) “ScienceShot: Animals That Live Without Oxygen” Science Magazine
7. John D. Cooper et al. (1986) A Trip Through Time: Principles of Historical Geology Page 180