How do planets sustain life? We explore this question by examining the evolution of Earth as an inhabited world, and by assessing the habitability of worlds beyond our own.
O2 in Earth’s Atmosphere and Oceans
Until about halfway through its history, Earth’s atmosphere was devoid of O2. The transition to a modern, O2-rich atmosphere – beginning with the so-called “Great Oxidation Event” that occurred ~ 2.4 billion years ago – was one of the most profound transitions the planet has undergone. While it was caused by life and paved the way for life like ours, we do not understand why it happened when it happened. Nor do we fully understand the causes and consequences of later variations in ocean and atmosphere O2.
In our research, we: seek evidence of the earliest “whiffs” of O2 to learn when photosynthesis began to pump O2 into the environment; examine the interactions between biological production and geological consumption of O2; and develop new “redox proxy” methods to examine changes in O2 in the environment through time.
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.
Elements and Evolution
Living things are made up of a distinct subset of chemical elements from the Periodic Table. These include C, H, O, N, P, and S – the major elements in DNA, RNA, proteins, and cellular structures – as well as a host of trace elements, such as Fe, Cu, Zn, and Mo, that are important enzyme cofactors. The abundances of many of these elements in the oceans and at Earth’s surface change with time, in large part as a consequence of changes in O2. The abundances may also differ on other Earth-like planets, as a consequence of variations in element abundances among the stars.
We are interested in the complex relationships between the chemical requirements of life and these variations in environmental abundances, leading us to: examine the “plasticity” of life’s use of particular elements; determine the compositions of organisms in extreme environments; assess the effects of environmental element variations on biological evolution in Earth’s past; and consider the consequences for life on other planets.
Learn more about this research:
- Web site of the NASA Astrobiology Institute “Follow the Elements” team at ASU (PI: Anbar)
- Web site of the NASA Astrobiology Institute’s “Stellar Stoichiometry Workshop” at ASU, 2012
- “Proterozoic ocean chemistry and evolution: a bioinorganic bridge?” Anbar and Knoll, Science (2002)
- “Elements and Evolution” Anbar, Science (2008)
- “Coevolution of metal availability and nitrogen assimilation in cyanobacteria and algae” Glass et al., Geobiology (2009)
- The “arsenolife” controversy – Wolfe Simon et al. + comments + reply, Science (2011)
- “Bioavailability of zinc in marine systems through time” Scott et al., Nature Geo. (2013)