Introduction to Geochemistry
Introduction to Geochemistry
Introduction to Geochemistry
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Explaining Cosmic Abundances<br />
! H and He are most abundant<br />
• Because they were formed in the Big Bang<br />
! Exponential decrease in abundance of first 50 elements<br />
• Reflects decreased productivity of He capture processes<br />
! Lower abundances of heavier elements<br />
• Caused by sluggishness of neutron capture reactions in normal stars<br />
! Greater stability of nuclides with even-numbered numbers of pro<strong>to</strong>ns and/or<br />
neutrons<br />
• Nucleons with paired spins have stronger nuclear binding affinities<br />
! Low abundances of Li, Be, B<br />
• Because production processes tend <strong>to</strong> bypass these elements, also they are<br />
destroyed by nucleon bombardment inside the star
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