Astrobiologia na Terra
Posted: 14 Apr 2010 09:10 PM PDT
Scientist find life in a lake of asphalt that is the closest thing on Earth to the hydrocarbon seas on Titan.
Pitch Lake is a poisonous, foul smelling, hell hole on the Caribbean island of Trinidad and Tobago. The lake is filled with hot asphalt and bubbling with noxious hydrocarbon gases and carbon dioxide. Water is scarce here and certainly below the levels normally thought of as a threshold for life.
These alien conditions have made Pitch Lake a place of more than passing interest to astrobiologists. Various scientists have suggested that it is the closest thing on Earth to the kind of hydrocarbon lakes that we can see on Saturn's moon Titan. Naturally, these scientists would very much like to answer the question of what kind of life these places can support.
Today, Dirk Schulze-Makuch from Washington State University and a few buddies provide an answer. Pitch lake, they say, is teaming with microbial life. They say that, on average, each gram of goo in the lake contains some 10^7 living cells.
These bugs are unlike anything we normally see on Earth. Analysis of gene sequences from these creatures show that they are single celled organisms such as archea and bacteria. They thrive in an oxygen-free environment with very little water, eating hydrocarbons and respiring with metals.
This may be the first time life has cropped up in hydrocarbon lakes on Earth's surface but these kinds of creepy crawlies have previously reared their heads in hydrocarbon samples from subsea oil wells. Which is another reason they are of interest. Just how microbial organisms can degrade and process of oil reservoirs is poorly understood. A better understanding could lead to a number of advances in techniques for things like microbial remediation.
But the most exciting implication of this discovery is for the possibility of life on Titan. There is a growing sense that Titan may have all the ingredients for life: thermodynamic disequilibrium, abundant carbon-containing molecules and a fluid environment.
And there is also evidence that liquid water may not be as important as everybody has assumed. Schulze-Makuch and co point to recent evidence that some microorganisms can make there own water by chewing on various hydrocarbons. However it is not yet clear how much water the bugs in Pitch Lake require. Although there is very little water here, it's just possible that the organisms are confined to regions where the water content is higher, as happens with ice-bound colonies in frozen lakes and glaciers. More work needs to be done on this.
Nevertheless, this is an exciting discovery and further study of the extraordinary residents of Pitch Lake will throw new light on all these questions. As Schulze-Makuch and co put it: "Our research is a starting point on investigating what life's principle constraints are in a hydrocarbon matrix and whether the hydrocarbon lakes on Titan could possibly contain life."
Ref: arxiv.org/abs/1004.2047: Microbial Life in a Liquid Asphalt Desert