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Have distal impact ejecta changed through geologic time?

Bruce M. Simonson and Paul Harnik
Have distal impact ejecta changed through geologic time?
Geology (Boulder) (November 2000) 28 (11): 975-978


Sand-size spherules of former silicate melt have been identified in approximately 10 thin Early Archean to Paleoproterozoic layers that appear to be reworked ejecta from large impacts. Melt spherules are common in Phanerozoic layers of distal impact ejecta, but the aggregate thickness of spherules in early Precambrian layers is generally 10 to 100 times greater, and they display textures rarely seen in Phanerozoic spherules. These contrasts suggest secular variations in the nature of both impactors and target materials, such as a progressive decrease in the size of impactors and a progressive increase in the fraction of Earth's surface covered by continental crust.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 28
Serial Issue: 11
Title: Have distal impact ejecta changed through geologic time?
Affiliation: Oberlin College, Department of Geology, Oberlin, OH, United States
Pages: 975-978
Published: 200011
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 35
Accession Number: 2000-075401
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Paleontological Research Institution, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200024
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