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Because the core was recovered from deep underground, it contains
materials untouched by the atmosphere for billions of years. After
retrieval, the scientists sliced the core longitudinally for analysis.
Study results appeared in a pair of papers in the journal
Science.
The UCR contribution:
Geochemists Timothy Lyons, Steven Bates, and Clinton Scott of the UCR
Department of Earth Sciences - working with
teams from Arizona State University and the universities of Maryland,
Washington, and Alberta - generated elemental
and isotopic data that provide indirect, or proxy, evidence for the
evolving atmosphere and its relationship to the early evolution of
life.
�This is the earliest convincing record for an ephemeral accumulation
of oxygen in the biosphere before its irreversible rise beginning 2.4
billion years ago,� said Lyons, a professor of biogeochemistry.
Scott, a graduate student working with Lyons, used metals in the
ancient ocean - now trapped in sedimentary
rocks - as proxies for the amount of oxygen in
the early ocean and atmosphere. His doctoral research provided a
baseline for the Australian samples, showing that the 2.5 billion-year
old rocks look more like those from younger times when oxygen was
higher in the atmosphere.
These results revealed to the UCR geochemists and their colleagues at
Arizona State University that oxygen increased significantly but
briefly 100 million years before its permanent place in Earth�s
atmosphere.
Working principally with colleagues at the University of Maryland,
Bates, a research associate, and Lyons analyzed sulfur present in the
Australian rocks as another fingerprint of oxygen concentrations at
Earth�s surface. Their analysis of the sulfur also confirmed that the
world changed briefly but importantly 2.5 billion years ago, presaging
the life-affirming oxygenation of the atmosphere 100 million years
later.
�We were surprised to see evidence of increasing oxygen in rocks so
old,� Lyons said. �And the fact that two independent lines of evidence
point in the same direction suggests that Earth�s most dramatic shift
in atmospheric composition and its relationship to the evolution of
life began earlier and was more complex than most imagined.�
Tim Lyons joined UCR�s Department of
Earth Sciences almost three years ago. As a geochemist specializing in
studies of how elements cycle in the ocean and atmosphere and their
cause-and-effect relationships with the evolution of early life, he
uses elemental and isotopic methods developed through studies of
modern oxygen-poor settings, such as the Black Sea. These geochemical
tools are then turned toward fundamental questions about Earth�s early
history recorded in the chemical properties of rocks formed many
millions to billions of years ago.
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