Abstract:
:The temporal distribution of the major extinctions over the past 250 million years has been investigated statistically using various forms of time series analysis. The analyzed record is based on variation in extinction intensity for fossil families of marine vertebrates, invertebrates, and protozoans and contains 12 extinction events. The 12 events show a statistically significant periodicity (P less than 0.01) with a mean interval between events of 26 million years. Two of the events coincide with extinctions that have been previously linked to meteorite impacts (terminal Cretaceous and Late Eocene). Although the causes of the periodicity are unknown, it is possible that they are related to extraterrestrial forces (solar, solar system, or galactic).
journal_name
Proc Natl Acad Sci U S Aauthors
Raup DM,Sepkoski JJ Jrdoi
10.1073/pnas.81.3.801subject
Has Abstractpub_date
1984-02-01 00:00:00pages
801-5issue
3eissn
0027-8424issn
1091-6490journal_volume
81pub_type
杂志文章abstract::Plasmids have been constructed to generate substrates for the study of proteinases 2A and 3C of poliovirus. They contain the P1 (capsomer precursor) region of the poliovirus genome or P1 and part of P2 (a nonstructural precursor), which can be transcribed and translated in vitro. A transcript containing the entire 5' ...
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
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更新日期:1989-11-01 00:00:00
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journal_title:Proceedings of the National Academy of Sciences of the United States of America
pub_type: 杂志文章
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更新日期:1997-11-11 00:00:00