Decline and fall of the empire.

"Are they worlds, or are they mere masses of matter? Are physical forces alone at work there or has evolution begotten something more complex, something not unakin to what we know on Earth as life? It is in this that lies the peculiar interest of Mars." Percival Lowell (in ref. 1, p. 3)     

Comet dust as a source of amino acids at the Cretaceous/Tertiary boundary

Large amounts of apparently extraterrestrial amino acids have been detected recently in rocks at the Cretaceous/Tertiary (K/T) boundary at Stevns Klint, Denmark. The amino acids were found a few tens of centimetres above and below the boundary layer, but were absent in the boundary clay itself. If one supposes that these compounds were carried to the Earth by the giant meteorite thought to have impacted at the end of the Cretaceous, some puzzling questions are raised: why weren't the amino acids incinerated in the impact, and why are they not present in the boundary clay itself? Here we suggest that the amino acids were actually deposited with the dust from a giant comet trapped in the inner Solar System, a fragment of which comprised the K/T impactor. Amino acids or their precursors in the comet dust would have been swept up by the Earth both before and after the impact, but any conveyed by the impactor itself would have been destroyed. The observed amino acid layers would thus have been deposited without an impact.     

Annihilation of ecosystems by large asteroid impacts on the early Earth

Large asteroid impacts produced globally lethal conditions by evaporating large volumes of ocean water on the early Earth. The Earth may have been continuously habitable by ecosystems that did not depend on photosynthesis as early as 4.44 Gyr BP (before present). Only a brief interval after 3.8 Gyr exists between the time when obligate photosynthetic organisms could continuously evolve and the time when the palaeontological record indicates highly evolved photosynthetic ecosystems.     

Ignition of global wildfires at the Cretaceous/Tertiary boundary

An impressive amount of evidence supports the proposal of Alvarez et al. that the Cretaceous era was ended abruptly by the impact of a comet or asteroid. The recent discovery of an apparently global soot layer at the Cretaceous/Tertiary boundary indicates that global wildfires were somehow ignited by the impact. Here we show that the thermal radiation produced by the ballistic re-entry of ejecta condensed from the vapour plume of the impact could have increased the global radiation flux by factors of 50 to 150 times the solar input for periods ranging from one to several hours. This great increase in thermal radiation may have been responsible for the ignition of global wildfires, as well as having deleterious effects on unprotected animal life.