Co-Evolution of Atmospheres, Life, and Climate
Journal article, 2010
After Earth's origin, our host star, the Sun, was shining 20-25% less brightly than today. Without greenhouse-like conditions to warm the atmosphere, our early planet would have been an ice ball, and life may never have evolved. But life did evolve, which indicates that greenhouse gases must have been present on early Earth to warm the planet. Evidence from the geological record indicates an abundance of the greenhouse gas CO2. CH4 was probably present as well; and, in this regard, methanogenic bacteria, which belong to a diverse group of anaerobic prokaryotes that ferment CO2 plus H-2 to CH4, may have contributed to modification of the early atmosphere. Molecular oxygen was not present, as is indicated by the study of rocks from that era, which contain iron carbonate rather than iron oxide. Multicellular organisms originated as cells within colonies that became increasingly specialized. The development of photosynthesis allowed the Sun's energy to be harvested directly by life-forms. The resultant oxygen accumulated in the atmosphere and formed the ozone layer in the upper atmosphere. Aided by the absorption of harmful UV radiation in the ozone layer, life colonized Earth's surface. Our own planet is a very good example of how life-forms modified the atmosphere over the planets' lifetime. We show that these facts have to be taken into account when we discover and characterize atmospheres of Earth-like exoplanets. If life has originated and evolved on a planet, then it should be expected that a strong co-evolution occurred between life and the atmosphere, the result of which is the planet's climate.
Biomarker
2-dimensional model
long-term
Atmospheres
Climate
habitable zones
Exoplanets
middle-atmosphere
evolution
earth-like planets
halogen occultation experiment
hydrogen
ozone
Early Earth
methane
Author
J. L. Grenfell
German Aerospace Center (DLR)
H. Rauer
German Aerospace Center (DLR)
Technische Universität Berlin
F. Selsis
University of Bordeaux
L. Kaltenegger
Harvard-Smithsonian Center for Astrophysics
C. Beichman
Jet Propulsion Laboratory, California Institute of Technology
W. Danchi
National Aeronautics and Space Administration (NASA)
C. Eiroa
Universidad Autonoma de Madrid (UAM)
M. Fridlund
European Space Research and Technology Centre (ESA ESTEC)
T. Henning
Max Planck Society
T. Herbst
Max Planck Society
H. Lammer
Institut fur Weltraumforschung
A. Leger
University of Paris-Sud
René Liseau
Chalmers, Department of Radio and Space Science, Radio Astronomy and Astrophysics
J. Lunine
University of Arizona
F. Paresce
Istituto nazionale di astrofisica (INAF)
A. Penny
STFC Rutherford Appleton Laboratory
A. Quirrenbach
Heidelberg-Königstuhl State Observatory
H. Rottgering
Leiden University
J. Schneider
Observatoire de Paris-Meudon
D. Stam
Netherlands Institute for Space Research (SRON)
G. Tinetti
University College London (UCL)
G. J. White
Open University
STFC Rutherford Appleton Laboratory
Astrobiology
1531-1074 (ISSN)
Vol. 10 1 77-88Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Roots
Basic sciences
DOI
10.1089/ast.2009.0375