منابع مشابه
Fungal proliferation at the Cretaceous-Tertiary boundary.
The evolution of life on Earth has been interrupted by several mass extinction events. The Cretaceous-Tertiary (K-T) extinction [65 million years ago (Ma)] is associated with the impact of a large bolide (1). On the basis of extensive data (2–4), the K-T boundary is characterized by a palynological extinction horizon coincident with a geochemical marker bed commonly succeeded by a bed rich in f...
متن کاملPlacental mammal diversification and the Cretaceous-Tertiary boundary.
Competing hypotheses for the timing of the placental mammal radiation focus on whether extant placental orders originated and diversified before or after the Cretaceous-Tertiary (KT) boundary. Molecular studies that have addressed this issue suffer from single calibration points, unwarranted assumptions about the molecular clock, andor taxon sampling that lacks representatives of all placental ...
متن کاملAnalysis of the cretaceous-tertiary boundary clay: methodology questioned.
ic outflow (38), also thought to regulate immune function (39j. Although knowledge of the precise involvement of the immune system in surveillance against tumors is limited, there is evidence to suggest that NK cells play a pivotal role (6). In this regard, we found that the same footshock stress regimen which causes a naltrexone-sensitive suppression of NK activity also enhances development of...
متن کاملProximal cretaceous-tertiary boundary impact deposits in the Caribbean.
Trace element, isotopic, and mineralogic studies indicate that the proposed impact at the Cretaceous-Tertiary (K-T) boundary occurred in an ocean basin, although a minor component of continental material is required. The size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact-wave deposits suggest an impact between the Americas. Coarse boun...
متن کاملEmplacement of cretaceous-tertiary boundary shocked quartz from chicxulub crater.
Observations on shocked quartz in Cretaceous-Tertiary (K-T) boundary sediments compellingly tied to Chicxulub crater raise three problems. First, in North America shocked quartz occurs above the main K-T ejecta layer. Second, shocked quartz is more abundant west than east of Chicxulub. Third, shocked quartz reached distances requiring initial velocities up to 8 kilometers per second, correspond...
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ژورنال
عنوان ژورنال: Episodes
سال: 1979
ISSN: 0705-3797,2586-1298
DOI: 10.18814/epiiugs/1979/v2i4/004