Biology
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p33c..04k&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P33C-04
Biology
[0406] Biogeosciences / Astrobiology And Extraterrestrial Materials, [5210] Planetary Sciences: Astrobiology / Planetary Atmospheres, Clouds, And Hazes, [5225] Planetary Sciences: Astrobiology / Early Environment Of Earth
Scientific paper
Earth has the peculiar property of remaining continuously habitable in spite of severe climate change throughout its 4.6 billion year (Ga) history. Life on this planet also has a resilient history, originating soon after Earth cooled and surviving many threats to its existence. In the anoxic Archean (2.8 Ga), the biological activity of methanogens resulted in greenhouse warming by methane and other hydrocarbons to counteract the 20% luminosity reduction from the faint young Sun, leading to the photochemical production of a shielding stratospheric organic haze. A negative feedback loop between methanogen activity and haze thickness maintained warm surface temperatures in the late Archean. The rise of atmospheric oxygen (2.4 Ga) following growth in photosynthesis by cyanobacteria triggered a global glaciation and may have been the most devastating climate change in Earth's history, yet the biosphere recovered to a richly oxic environment in which breathable life became possible. The adaptation of life to a range of ecological niche space, including extreme environments, has contributed to the persistence of life through mass extinctions, most significantly the Permian-Triassic extinction ~250 million years ago (Ma) when up to 96% of marine species and 70% of terrestrial vertebrates vanished. Abrupt climate change has also challenged the survival of life, including the Neoproterozoic Snowball Earth episode (~650 Ma) where evidence from glacial deposits suggests the tropical oceans froze over. During this period life may have thrived in a manner analogous to the Antarctic dry valleys, where sufficient sunlight penetrates the ice to allow photosynthesis. Present day climate change is marked by human influence on atmospheric composition and widespread loss of biodiversity, but even the most severe projected scenarios fall short of the global ecological catastrophes experienced in Earth's past--events from which life has always recovered. The challenge of global warming, then, is not to protect life on this planet but to ensure our own survival and a sustainable future.
Haqq-Misra Jacob
Kasting James F.
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