Dr. Pavlov's Research

Early Earth

Early Earth's atmosphere should have been rich in greenhouse gases to offset the faintness of

the young Sun. However, there is still a significant debate on which greenhouse gas helped to save

the early Earth from freezing. I explored the possibility of high methane abundance in the Archean/Proterozoic. Methane is expected to accumulate in the low-oxygen atmospheres and in

combination with large atmospheric CO2 abundance could keep the Earth above freezing:

Pavlov et al. (2000) "Greenhouse warming by CH4 in the atmosphere of early Earth" JGR, vol. 105,  p. 11,981-11,990.

Pavlov et al. (2001) "UV shielding of NH₃ and O₂ by organic hazes in the Archean atmosphere." JGR vol. 106, p. 23,267-23,287.

Pavlov et al. (2001) "Organic haze in Earth’s early atmosphere: source of low-¹³C late Archean kerogens?" Geology 29, p. 1003-1006.

Pavlov et al. (2003), "Methane-rich Proterozoic atmosphere?" Geology, 31, p. 87-90.

There is plenty of work to be done here given that hydrocarbon aerosols could form in such CH4-CO2

rich atmospheres and profoundly affect climate and photochemistry. Also all climate calculations has

to be redone with a 3-D model - a good project for an ambitious graduate student who is not afraid of

computer models.

Sulfur Isotopes

Anomalous fractionation (sometimes called mass-independent fractionation or MIF) in sulfur isotopes

was observed in the ancient terrestrial rocks, martian meteorites and in Antarctic ice-cores. MIF

makes scientists excited because it can be produced effectively only in the gas phase - atmosphere.

Therefore MIF in ancient rocks and martian meteorites is a direct signature of the ancient terrestrial

and martian atmospheres. The question is "Can we interpret this signature and place reasonable

constraints on the composition of the ancient Earth's atmosphere?"

Pavlov and Kasting (2002) "Mass-independent fractionation of sulfur isotopes in Archean sediments: Strong evidence for an anoxic Archean atmosphere." Astrobiology 2, p. 27-41.

Pavlov et al. (2005) "Mystery of the volcanic mass-independent sulfur isotope fractionation signature in the Antarctic ice-core." GRL doi10.1029/2005GL022784.

This field has to be advanced on two levels. First, the proper experiments have to be done by several independent groups. So far only one group did photochemical experiments trying to reproduce sulfur

MIF. Second, the theoretical basis for the sulfur MIF is still obscure and requires detailed quantum

mechanical calculations.   

Mass-extinctions

Mass-extinctions are fascinating and enigmatic phenomena in the Earth history. I am particularly

interested in various triggering mechanisms. Scientific community is split between proponents of

the extraterrestrial (impacts, superflares) and terrestrial (large volcanic eruptions, climate change)

triggers. As always, the challenge is not only to propose a trigger but also to point for possible

imprints of such trigger in the geologic record.   

A. A. Pavlov, A. K. Pavlov, M. J. Mills, V. M. Ostryakov, G. I. Vasilyev, O. B. Toon, Catastrophic ozone loss when “shields” are down. GRL 32 (1), Art. No. L01815, 2005.

L. R. Kump, A. A. Pavlov and M. A. Arthur, Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia. Geology 33,  397-400, 2005.

Hydrogen escape

Hydrogen escape from planetary atmospheres is a very important process which can control the

availability of water on a particular planet and the overall chemical composition of a planetary

atmosphere. It is still under debate at what rate hydrogen was lost to space from the atmospheres

of the early Earth, Mars and Venus. 

F. Tian, Toon O. B., Pavlov A. A., DeStark H., Transonic Hydrodynamic Escape of Hydrogen from Extrasolar Planetary Atmospheres. Astrophysical Journal 621 (2), 1049-1060, 2005.

F. Tian, Toon O. B., Pavlov A. A., DeStark H., A hydrogen-rich early Earth atmosphere. Science 308, 1014-1017, 2005.

Snowball Earth

Pavlov et al. (2005), "Passing through Giant Molecular Cloud – Effects on Climate. Possible link to Snowball Glaciations?" GRL 32 (3), Art. No. L03705, 2005.

Life on Mars

A. K. Pavlov, V. L. Kalinin, A. N. Konstantinov, V. N. Shelegedin, A. A. Pavlov, Was Earth ever infected by Martian biota? Clues from radioresistant bacteria. Astrobiology, 6(6): 911-918, 2006.