Abstract/Details

Large impact events and atmospheric evolution on the terrestrial planets


1989 1989

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Abstract (summary)

This dissertation is an exploration of the effects of the collision of large asteroids and comets on the atmosphere of the Earth and Earthlike planets. The first task undertaken is the characterization of the impact rates in the inner solar system during the present time, and during the first billion years of Solar System history when the flux was changing rapidly. Once defined, these fluxes are used to model the long term cumulative effect of multiple impacts on planetary atmospheres.

The implications of cometary impacts on evolution of the water and deuterium abundances on Venus are examined. The short lifetime of water on Venus suggests that the water abundance is in a quasi-steady-state balance between loss by escape and replenishment by infall. In addition, the observed deuterium-to-hydrogen ratio on Venus is consistent with a steady state and does not necessarily imply a past water excess. Results are presented of a model incorporating a stochastic cometary source and nonthermal escape of hydrogen that produces the observed water abundance and D/H ratio. The stochastic variability of each of these quantities is shown to be large. Water on Venus is likely to be in a near steady state mediated by large comet impacts. The early history of water on the planet has been obscured by a history of random impacts.

A study of the effects of impact-generated dust clouds on the primitive Earth leads to the conclusion that such clouds were significant perturbers of the early climate. The Earth was shrouded by an optically-thick dust cloud for $\approx$150-250 m.y. During this time the surface temperature was equal to the planetary equilibrium temperature unless significant heating by impacts or surface heat flow existed beneath the dust cloud. An admixture of a few per cent of organic materials in the cloud may have significantly lowered the planetary bond albedo, thereby raising the equilibrium temperature. The epoch of continuous dust shrouding was followed by a period of stochastically intermittent dust clouds occuring at greater intervals as the early intense bombardment subsided towards the present day flux.

Indexing (details)


Subject
Geology;
Astronomy;
Astrophysics
Classification
0372: Geology
0606: Astronomy
0606: Astrophysics
Identifier / keyword
Pure sciences; Earth sciences
Title
Large impact events and atmospheric evolution on the terrestrial planets
Author
Grinspoon, David Harry
Number of pages
210
Publication year
1989
Degree date
1989
School code
0009
Source
DAI-B 50/05, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
Advisor
Lewis, John S.
University/institution
The University of Arizona
University location
United States -- Arizona
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
8915959
ProQuest document ID
303738091
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/303738091
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