The vast majority of life on Earth is heavily dependent on the availability of molecular oxygen (O2). Modern life thrives in its presence, and is pushed to its limits when it goes away.
Our group is very much interested in Earth's oxygenation history. Lucky for us, many fundamental questions on this topic remain unanswered. When did O2 first appear at Earth's surface? Once it was available, how stable was it in the atmosphere? What about in the oceans? AnbarLab staff and students have many projects dedicated to addressing these questions.
Our window to early-Earth: Ancient marine Sedimentary Rocks
Certain marine sedimentary rocks capture and preserve key chemical details of Earth's ancient oceans and atmosphere. For example, the abundance of redox-sensitive trace metals can provide invaluable information about changes in atmospheric and oceanic oxygenation that occurred when the rock was originally deposited. Our group uses drill cores from all over the world to assess changes in these elemental abundances at various points in geologic time.
Direct Clues: isotopes
Some processes in nature prefer to use versions of an element with more or less neutrons, referred to in chemistry as "isotopes". If this happens, evidence is sometimes left behind in the ancient rock record.
If these processes are linked to the availability of O2, investigating these clues becomes a powerful tool in reconstructing Earth's oxygen history.
To date, our group has developed and refined the use of Fe, Mo, and U isotopes as paleoredox proxies for perturbations in ancient Earth O2.
Indirect clues: Experiments
Experiments under simulated early-earth conditions provide unrivaled information about how changes in the environment are reflected in the ancient rock record.
For example, experiments can be conducted under O2-deficient conditions to test the viability of alternate oxidation pathways, or to estimate the rate of elemental delivery to the ocean in a dominantly anoxic atmosphere.
Our analytical tool of choice: mass spectrometry
Bulk elemental abundances of samples can be directly measured using a quadrupole inductively-coupled plasma mass spectrometer (ICPMS).
For isotope ratio measurements, we instead turn to the more powerful Neptune multi-collector ICPMS (MC-ICPMS).
For details about our instrumentation, sample preparation, and analyses, please visit the website of the W. M. Keck Foundation Laboratory for Environmental Biogeochemistry (LINK).
Learn more about this research:
- Web site of the NSF “Dynamics of Earth Surface Oxygenation” project based at ASU (PI: Anbar)
- Web site of the Australian project of the Agouron Institute Drilling Program
- “A whiff of oxygen before the Great Oxidation Event?” Anbar et al., Science (2007)
- “Metal stable isotopes in paleooceanography” Anbar and Rouxel, Ann. Rev. Earth Planet. Sci. (2007)
- “Reconstructing paleoredox conditions through a multitracer approach: the key to the past is the present” Severmann and Anbar, Elements (2009)
- “Rapid expansion of oceanic anoxia immediately before the end-Permian mass extinction” Brennecka et al., Proc. Nation. Acad. Sci. (2011)
- Forbes interview about O2 and the NSF FESD project.