• Publications
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Cratering Rates in the Outer Solar System
  • K. Zahnle
  • Geology, Environmental Science
  • 1 September 1999
We have constructed a self-consistent study of cratering rates in the outer solar system. Two papers were written, one on cratering asymmetries on synchronously rotating satellites and the other onExpand
Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of Early Earth
TLDR
Expected irreversible oxidation (∼1012 to 1013 moles oxygen per year) may help explain how Earth's surface environment became irreversibly oxidized. Expand
Annihilation of ecosystems by large asteroid impacts on the early Earth
TLDR
The Earth may have been continuously habitable by ecosystems that did not depend on photosynthesis as early as 4.44 Gyr BP (before present), but only a brief interval after 3.8 Gyr exists between the time when obligate photosynthetic organisms could continuously evolve and thetime when the palaeontological record indicates highly evolved photosynthetics ecosystems. Expand
Carbon dioxide cycling and implications for climate on ancient Earth
The crustal Urey cycle of CO2 involving silicate weathering and metamorphism acts as a dynamic climate buffer. In this cycle, warmer temperatures speed silicate weathering and carbonate formation,Expand
Photochemistry of methane and the formation of hydrocyanic acid (HCN) in the Earth's early atmosphere
The photochemistries of methane and HCN are discussed in the context of the primitive terrestrial atmosphere, using a detailed numerical model. In the absence of abundant O2, absorption of solar EUVExpand
Nitrogen-enhanced greenhouse warming on early Earth
Early in Earth’s history, the Sun provided less energy to the Earth than it does today. However, the Earth was not permanently glaciated, an apparent contradiction known as the faint young SunExpand
The loss of mass‐independent fractionation in sulfur due to a Palaeoproterozoic collapse of atmospheric methane
We use a 1-D numerical model to study the atmospheric photochemistry of oxygen, methane, and sulfur after the advent of oxygenic photosynthesis. We assume that mass-independent fractionation (MIF) ofExpand
Why O2 is required by complex life on habitable planets and the concept of planetary "oxygenation time".
TLDR
It is argued that the oxygenation time is likely to be a key rate-limiting step in the evolution of complex life on other habitable planets, including Earth-like planets orbiting short-lived stars that end their main sequence lives before planetary oxygenation takes place. Expand
Emergence of a Habitable Planet
Abstract We address the first several hundred million years of Earth’s history. The Moon-forming impact left Earth enveloped in a hot silicate atmosphere that cooled and condensed over ∼1,000 yrs. AsExpand
Environmental Perturbations Caused by the Impacts of Asteroids and Comets
We review the major mechanisms proposed to cause extinctions at the Cretaceous-Tertiary geological boundary following an asteroid impact. We then discuss how the proposed extinction mechanisms mayExpand
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