Publication Date:
1997-07-25
Description:
Knowledge of the production history of cosmogenic nuclides, which is needed for geological and archaeological dating, has been uncertain. Measurements of chlorine-36/chlorine (36Cl/Cl) ratios in fossil packrat middens from Nevada that are radiocarbon-dated between about 38 thousand years ago (ka) and the present showed that 36Cl/Cl ratios were higher by a factor of about 2 before approximately 11 ka. This raises the possibility that cosmogenic production rates just before the close of the Pleistocene were up to 50% higher than is suggested by carbon-14 calibration data. The discrepancy could be explained by addition of low-carbon-14 carbon dioxide to the atmosphere during that period, which would have depressed atmospheric radiocarbon activity. Alternatively, climatic effects on 36Cl deposition may have enhanced the 36Cl/Cl ratios.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Plummer, M A -- Phillips, F M -- Fabryka-Martin, J -- Turin, H J -- Wigand, P E -- Sharma, P -- New York, N.Y. -- Science. 1997 Jul 25;277(5325):538-41.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9227999" target="_blank"〉PubMed〈/a〉
Keywords:
Animals
;
Atmosphere
;
Carbon Radioisotopes/analysis
;
Chlorine/*urine
;
Cosmic Radiation
;
*Fossils
;
Nevada
;
Radioisotopes/*urine
;
Sigmodontinae/*urine
;
Time Factors
Print ISSN:
0036-8075
Electronic ISSN:
1095-9203
Topics:
Biology
,
Chemistry and Pharmacology
,
Computer Science
,
Medicine
,
Natural Sciences in General
,
Physics
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