Bacteria in Deep Rocks, but not really Deep Rocks

Life is found in deepest layer of Earth's crust - environment - 18 November 2010 - New Scientist

www.newscientist.com

An expedition to the deepest layer of the Earth's oceanic crust has revealed an ecosystem living over a kilometre beneath our feet

Bacteria were found in a deep drill hole where life was not expected. Now Sam sent this to me and I think I read the abstract that day too. This guy Sam does some kind of computery work and he rides a bike, but he definately has a sensitive science antenna because it clearly quivered enough for him to recognize that this is a potentially important article.

The idea of microscopic life surviving, and even thriving, in pore spaces or tiny fractures deep underground is not new. Dr. Tom Kieft has been doing this for some time (http://infohost.nmt.edu/~biology/people/faculty/t_kieft/research.html) and his group has been going much deeper than the New Scientist story. The difference is that Dr. Kieft has started at the bottom of deep mines in South Africa (with plans to do similar studies at DUSEL in South Dakota) and drilling down to access even deeper depths. The depths his group could theoretically reach with the infrastructure of DUSEL make the New Scientist study look like they just scratched the surface...and they expect life as far as they can drill. 

So, what's the big deal? They say in the article that they didn't expect to find life in this Gabbro layer, which is right above the mantle. However, careful study of the little cartoon shows that they just hit the very top of the gabbro layer. The substantive difference between the basalt and the gabbro is minimal. There is a relatively small geochemical difference and the crystals are bigger. Both will possess very similar porosities and minerals that the bugs can use to survive. I think as long as the temperatures are low enough to allow proteins to function, there is sufficient chemistry for microbiota to process, and water, you will find life in earth. And life seems to find ways to push the limits of temperature, chemistry, and water that we think will allow them to survive. 


There was one little gem that they mentioned but did not elaborate. They only found bacteria, but no Archaea. Now Archaea are a type of single celled microscopic bug that look, smell and taste just like bacteria, which is why they were not included in the textbooks until recently. For example, Archaea are not to be found in my high school text books. But recent advances in cell culturing, genetic sampling of ground up DNA, and a phylogenetic analysis indicate that Archea are distinct from bacteria and our branch of the tree, eukarotes. Archaea are typically known as the extremophiles that have the ability to live in super-high temperatures or chemical environments that kill off all the other types of life. They also do a lot of interesting geochemistry that allows them to not only survive, but use poisonous gasses and chemicals to gain energy. 

Why, why, why are Archaea not present in the basalt layer? What kind of genetic advantage do bacteria have that allow them to live so deep? Is it possible that the Archaea simply were not detected? The authors do include a hypothesis that the bacteria migrated from oil reserves. But is it reasonable that bacteria would go from a very high hydrocarbon environment to a very sparse hydrocarbon environment? Why would Archaea not be capable of making the same evolutionary step? 

Understanding the evolution of microscopic single celled life on earth is important because it holds the spot at the root of our tree of life. You could also imagine that better understanding the conditions that these critters live and evolve under will be helpful when we investigate other planets, like Mars and Europa, for life. And that is exciting. I think there are some big holes in this particular story that are open to the researcher community. It will be interesting following this story over the next few years.