[meteorite-list] Discovery of distal ejecta from Sudbury impact event

[Paul H]

Discovery of distal ejecta from the 1850 Ma Sudbury
impact event
from "March Geology and GSA TODAY" media highlights
at:

http://www.eurekalert.org/pub_releases/2005-02/gsoa-mga022805.php
http://www.gsajournals.org/gsaonline/?request=get-current-toc&issn=0091-7613

Addison, W. D., and others, 2005, Discovery of 
distal ejecta from the 1850 Ma Sudbury impact 
event. Geology: Vol. 33, No. 3, pp. 193–196.

 Addison et al. announce the discovery of impact 
ejecta from the Sudbury, Ontario, Canada, 
structure, the second largest and third or fourth 
oldest extraterrestrial Earth impact site. At 1.85 
billion years old, these Paleoproterozoic ejecta 
are three times older than the previous oldest 
dated ejecta linked to a specific impact (Acraman, 
Australia, 0.59 billion years old). It is also larger 
than the well-known Chicxulub, Mexico (0.065 
billion years old) impact linked to the extinction 
of the dinosaurs and many other species. The 
young Chicxulub impact, particularly its well-
preserved worldwide ejecta debris layers, have 
produced criteria to judge other large ejecta 
deposits. Foremost is the occurrence of sets of 
microscopic parallel lamellae in quartz and 
feldspar grains produced by the intense shock 
generated at the point of impact. Secondarily, 
the impact generated a megaplume of vaporized, 
melted, and crushed crustal rocks, creating molten 
droplets containing bubbles of gas, and larger 
accreted balls of dust and rock shards called 
impact accretionary lapilli. These features, and 
more, are seen in the Sudbury debris. The debris 
(ejecta) studied here, landed 650 km west northwest 
of Sudbury near Thunder Bay, Ontario, Canada, and 
875 km west of Sudbury near Hibbing, Minnesota, 
United States. This huge impact likely deposited 
debris all around Earth, but it is very difficult to 
find because so much of the evidence has been 
destroyed in the recycling of Earth's crust by plate 
tectonics. Life at the time of the Sudbury impact 
was confined to the oceans and consisted of 
unicellular and colonial unicellular organisms. So 
far, Addison et al. have found no evidence of 
extinction of this life. However, future studies may 
link this impact and its ejecta with changes in the c
lassic Gunflint Iron Formation unicellular organisms 
and their photosynthetic microbial mats, which 
helped produce Earth's atmospheric oxygen.


	
		
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