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Australia: The Land Where Time Began |
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Jack Hills - Light Carbon Reservoir Recorded in Zircon-Hosted Diamond
A unique opportunity to investigate the Earth’s oldest known carbon
reservoir has been provided by a recent discovery of diamond-graphite
inclusions in the oldest known zircon grains, dating to up to 4,252 Ma,
from the metasediments of Jack Hills in Western Australia. In this paper
Nemchin et al. report the
results of ion probe analyses of these diamond-graphite inclusions. The
δ13CPDB values observed, expressed in the PeeDee
Belemnite standard, ranging from -5/ml to -58/ml with a median of
-31/ml. This extends beyond mantle values typically of around -6/ml to
values that are observed in metamorphic and some eclogitic diamonds that
have been interpreted to reflect deep subduction of low δ13CPDB
biogenic surface carbon. Inorganic chemical reactions (2) may also
produce low δ13CPDB values, which therefore means
they are not unambiguous evidence of life on Earth as early as 4,250 Ma.
Their results nevertheless suggest that a low δ13CPDB
reservoir may have existed on the early Earth in the deep past.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |