149 research outputs found
Atmospheric Evolution
Earth's atmosphere has evolved as volatile species cycle between the
atmosphere, ocean, biomass and the solid Earth. The geochemical, biological and
astrophysical processes that control atmospheric evolution are reviewed from an
"Earth Systems" perspective, with a view not only to understanding the history
of Earth, but also to generalizing to other solar system planets and
exoplanets.Comment: 34 pages, 3 figures, 2 tables. Accepted as a chapter in
"Encyclopaedia of Geochemistry", Editor Bill White, Springer-Nature, 201
Near miss: the importance of the natural atmospheric CO2 concentration to human historical evolution
Earth: Atmospheric Evolution of a Habitable Planet
Our present-day atmosphere is often used as an analog for potentially
habitable exoplanets, but Earth's atmosphere has changed dramatically
throughout its 4.5 billion year history. For example, molecular oxygen is
abundant in the atmosphere today but was absent on the early Earth. Meanwhile,
the physical and chemical evolution of Earth's atmosphere has also resulted in
major swings in surface temperature, at times resulting in extreme glaciation
or warm greenhouse climates. Despite this dynamic and occasionally dramatic
history, the Earth has been persistently habitable--and, in fact,
inhabited--for roughly 4 billion years. Understanding Earth's momentous changes
and its enduring habitability is essential as a guide to the diversity of
habitable planetary environments that may exist beyond our solar system and for
ultimately recognizing spectroscopic fingerprints of life elsewhere in the
Universe. Here, we review long-term trends in the composition of Earth's
atmosphere as it relates to both planetary habitability and inhabitation. We
focus on gases that may serve as habitability markers (CO2, N2) or
biosignatures (CH4, O2), especially as related to the redox evolution of the
atmosphere and the coupled evolution of Earth's climate system. We emphasize
that in the search for Earth-like planets we must be mindful that the example
provided by the modern atmosphere merely represents a single snapshot of
Earth's long-term evolution. In exploring the many former states of our own
planet, we emphasize Earth's atmospheric evolution during the Archean,
Proterozoic, and Phanerozoic eons, but we conclude with a brief discussion of
potential atmospheric trajectories into the distant future, many millions to
billions of years from now. All of these 'Alternative Earth' scenarios provide
insight to the potential diversity of Earth-like, habitable, and inhabited
worlds.Comment: 34 pages, 4 figures, 4 tables. Review chapter to appear in Handbook
of Exoplanet
Permo–Triassic boundary carbon and mercury cycling linked to terrestrial ecosystem collapse
Records suggest that the Permo–Triassic mass extinction (PTME) involved one of the most severe terrestrial ecosystem collapses of the Phanerozoic. However, it has proved difficult to constrain the extent of the primary productivity loss on land, hindering our understanding of the effects on global biogeochemistry. We build a new biogeochemical model that couples the global Hg and C cycles to evaluate the distinct terrestrial contribution to atmosphere–ocean biogeochemistry separated from coeval volcanic fluxes. We show that the large short-lived Hg spike, and nadirs in δ²⁰²Hg and δ¹³C values at the marine PTME are best explained by a sudden, massive pulse of terrestrial biomass oxidation, while volcanism remains an adequate explanation for the longer-term geochemical changes. Our modelling shows that a massive collapse of terrestrial ecosystems linked to volcanism-driven environmental change triggered significant biogeochemical changes, and cascaded organic matter, nutrients, Hg and other organically-bound species into the marine system
Was The Archean Biosphere Upside Down
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62929/1/329710a0.pd
Possible limits on the composition of the Archaean ocean
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62704/1/302518a0.pd
Carbon Geodynamic Cycle
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62503/1/303730b0.pd
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