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Speeding Up Evolution
Dr. Emma Bakes has all the time in the world---not Earth, however, but an exotic moon orbiting a distant planet in our solar system. Bakes, a SETI Institute scientist and NASA Astrobiology Institute (NAI) lead team member, studies the chemical evolution in the atmosphere of Titan, Saturn's giant satellite and the only known planetary companion in our solar system swaddled in a thick atmosphere. Rich in large, complex carbon- and nitrogen-bearing chemicals, Titan's dense smog-like haze is thought to be similar to the primitive atmosphere of early Earth. Inside Bakes' powerful Sun Microsystems processor, the smoggy shroud evolves at breakneck speed. Millions of years of complex chemical reactions condense into hours. And what results may help us learn more about how life emerged and survived on Earth.
Having a lab in a computer offers "instant gratification," says Bakes, whose work will also offer valuable insights to other astrobiologists. Modeling complex chemical processes on this distant moon could shed light on the emergence of life on early Earth and the transition of Earth's atmosphere from anoxic into one where molecular oxygen became freely available for complex, oxygen breathing species. The results of Bakes' computer simulation will add to the broad picture she and her colleagues on the Institute's NAI team are painting of life's co-evolution with its planetary environment.
Titan's Haze and the Early Earth
"The NAI project is concerned with something called nitrogenated heterocyclics," Bakes explains. "These are hexagons of carbon atoms with nitrogen atoms attached." In other words, large macro-molecules composed primarily of carbon interwoven with nitrogen, e.g. purines, pyrimidines, and pyrroles, for example. These macro-molecules have a tendency to clump, forming spherical aggregates Carl Sagan named "tholins." The macro-molecule and tholin haze forms a particularly effective UV screen on Titan, and may have served a protective role on early Earth.
Today, terrestrial biology is shielded from UV rays in large part by an atmospheric layer of ozone. Before the rise of oxygen on the early Earth, large fragile molecular precursors of life and early biology lacked the protective ozone shield, and the smog-like haze could have served as a UV screen that allowed the vulnerable bio-chemicals and early living systems to develop.
Not only do Bakes' models show that a Titan-like haze efficiently filters UV rays, but they also strongly suggest that the chemical reactions that result over time in such an atmosphere may have facilitated the rise of free oxygen by "clearing the deck" of reactive hydrogen. In the Titan simulations, atoms of hydrogen tends to pair-up, forming stable H2, which then leaves the atmosphere and dissipates into space. On the early Earth, this slow depletion of hydrogen would have allowed atoms of oxygen to pair-up in similar fashion rather than bond with hydrogen to form water. Enriched with oxygen, Earth's atmosphere was primed to support the rise of complex, oxygen breathing organisms and ultimately all of us, sentient beings who can conduct research into our own origins.
Studying the Origin of Life
While Titan may itself be lifeless, the biological implications of the organic chemistry taking place in the distant, smoggy world have fueled Bakes' own interest in biology. "I'm actually taking some biology classes at Foothill College," the physicist offered during a recent interview.
In addition to the NAI research, Bakes investigates structural properties of DNA and speculates that perhaps a helix is a universal configuration for life's instructions. "We always want to know where we come from," says Bakes of her investigations into life's origins. "And for me, just answering a few of those questions is very rewarding."
August 12, 2003