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Interview: Elemental evolution
15 April 2009
Ariel Anbar talks to May Copsey about fossils, Star Trek and life on Mars
Ariel Anbar is a biogeochemist in the department of chemistry and biochemistry and the school of earth & space exploration at Arizona State University, US and a member of the Metallomics editorial board. His research is focused on the chemistry of transition elements in the environment, and understanding how changes in bioessential elements during Earth's history have affected evolution.
What was it that inspired you to be a scientist?
Could you tell me about what is going on in your lab at the moment?
The core research in my group is geochemical and focuses on the development and application of novel methods for measuring natural variations in the concentrations and isotope compositions of transition metals in geological materials. Our major focus is to use such measurements to try to understand ancient environments and how the environment has changed with time. For example, we look at the isotopes of molybdenum in two and half billion year old rocks and measure how their abundances differ from those in similar rocks today. Those variations tell us about differences in chemical processes in the environment, such as the extent to which molybdenum interacted with oxygen in the atmosphere and oceans. So, from measurements of molybdenum isotopes in ancient rocks we can learn about the rise of oxygen in the ancient environment. To decipher how those changes in isotopic composition related to the amount of oxygen or other variables, you have to do laboratory experiments to figure out what it is that causes the isotopes to fractionate in plausible natural conditions. So we have a major laboratory research effort as well.
You've recently been looking at the oxygen content in the oceans, can you tell me more about that?
Molybdenum is an unusually redox-sensitive metal in the environment and so its concentrations and isotope compositions in ancient oceans vary as a function of oxygen. This has interesting implications beyond the use of molybdenum as a tracer of ancient oxygen. For example, today, among the transition metals, molybdenum is the most abundant in the oceans. However, it was much more scarce in ancient oceans. Molybdenum is important in many enzymes, so you can start to ask whether or not molybdenum scarcity affected the biosphere in the past. My group has been instrumental in measuring molybdenum isotope variations and the redox sensitivity of its isotope chemistry, and so now we're applying that knowledge to questions in evolution.
You've recently obtained funding from NASA, is that work related to looking at possible life on Mars?
I'm the leader of a NASA Astrobiology Institute (NAI) team at Arizona State University. This is one of the 14 teams that make up the NAI. The theme of our team is 'Follow the Elements'. For about a decade, in searching for habitable environments beyond those on Earth, NASA has had the mantra of 'Follow the Water'. But it's not enough to know if there was water there. That's a necessary condition, but not sufficient. What else makes a place habitable? One of the criteria in addition to water is the presence of the elements required for biology. Therefore, if you think that there was an ancient groundwater system in some location on Mars, we need to ask what we can infer about the nitrogen budget there, or the availability of phosphorus in that environment or in those ancient waters. Our team focuses on that topic. One of the goals we have is to help inform what it is that we really want to measure, what kind of materials we really want to look at and what concentrations of bioessential elements we really want to look for.
Looking back, what do you consider to be your most rewarding achievements?
When I started my independent academic career I gambled on this idea that transition metal isotopes would fractionate in the environment to a degree that was measurable. Many of my seniors told me I was a little crazy! The technology to measure the consequences of isotope sensitivities for carbon and oxygen has existed for 50 years. However, for transition metals, the challenge is that the difference in mass between isotopes as a percentage of the total mass is much smaller, so the size of fractionation is much smaller. It was a question of whether the technology existed to actually measure the variations and whether nature gives you the kind of chemistry that enables that fractionation to be realised. So I took this gamble that the development of ICP mass spectrometry combined with multiple detectors had matured to the point that we could make sufficiently precise measurements, and that an assistant professor could actually build a career doing this. That gamble has paid off very nicely and I'm pretty proud of the role I played being one of the early leaders in this field.
Geochemists were generally unaware of metal use in biology, and, with some notable exceptions, biochemists and bioinorganic chemists tended to pay little attention to the evolutionary implications of metal use in biology. So I wrote a paper in 2002 in Science1 with Andy Knoll, a paleobiologist at Harvard University, postulating that molybdenum availability in the oceans should have changed with time and this should have had an impact on the nitrogen cycle. We further argued that this connection might explain a puzzle of eukaryote evolution. We still aren't sure if that idea is correct, but the idea intrigued others. Increasingly I see other people publishing really good papers in which they've developed other ideas that link metals and evolution. I like to think that my work had some influence on getting people to develop those ideas.
As a research community, what do you think is the best way to encourage future communication across the sciences?
You need to get people to talk to each other, of course, but even before that you have to get people to really respect each other's research. That is the first challenge which needs to be overcome. I think this is often the biggest barrier, getting over the question of 'why would that be important?' when one specialist encounters another.
Prestigious journals play an important role in breaking these barriers down. If you get something published in these journals it usually leads to respect across disciplines, so that helps. Journals that explicitly try to build bridges across disciplines, like Metallomics, play a vital role too.
What advice do you have for young scientists?
What do you like doing when you're not in the lab?
I'm a simple person - I enjoy hanging out with my family. I have an eight year old and five year old, so I can often be found watching an old Star Trek episode with them. I was a Star Trek fan as a kid. That definitely influenced my choice of career!
1. A. D. Anbar and A. H. Knoll, Science, 2002, 297, 1137
Ariel Anbar's homepage
Research and recent publications of Ariel Anbar
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Also of interest
Isotope fractionation during microbial metal uptake measured by MC-ICP-MS
L. E. Wasylenki, A. D. Anbar, L. J. Liermann, R. Mathur, G. W. Gordon and S. L. Brantley, J. Anal. At. Spectrom., 2007, 22, 905
Assimilatory and dissimilatory processes of microorganisms affecting metals in the environment
Laura J. Liermann, Elisabeth M. Hausrath, Ariel D. Anbar and Susan L. Brantley, J. Anal. At. Spectrom., 2007, 22, 867