Life's First Scalding Steps

Science News, Jan 9, 1999 by Sarah Simpson

Hazen and Morowitz assembled specialists, each capable of attacking the origins-of-life question from a different area of expertise, from several institutions. What's more, they are backed by NASA's new Astrobiology Institute, which is exploring where and how life may exist throughout the universe. "We're trying to use a systematic approach to what is a huge and complicated field," Hazen says.

Their approach recently took advantage of Brandes' focus on nitrogen, another important life-building element. Organisms gain nitrogen through reactions involving ammonia, a simple combination of nitrogen and hydrogen. In Wachtershauser's theoretical assembly line, ammonia is a key player: It helps convert compounds from the citric acid cycle into amino acids. Yet few had expected ammonia to survive the vent inferno.

Brandes led the way to proving that expectation false. In the tiny gold capsules, he mixed water with nitrogen oxides presumed to be present in ancient oceans and added Wachtershauser's sulfide minerals to jump-start any reactions. Inside the bomb, heating elements and pneumatic pistons subjected the capsules to conditions typical of hydrothermal vents. After only 15 minutes at 500 [degrees] C and a pressure 500 times that at the planet's surface, the experiment created ammonia--and lots of it. What's more, the ammonia was stable up to a fiery 800[degrees]C. The team reported their findings in the Sept. 24, 1998 NATURE.

Once the Carnegie researchers knew that the hydrothermal mix could create ammonia, they turned to the next step, in which ammonia combines with pyruvic acid to build the amino acid alanine. Again, the scientists mixed their ingredients in a gold capsule and heated and squeezed them. Even without a catalyst, as much as 40 percent of the pyruvic acid converted to alanine.

Amino acids made at hydrothermalvent conditions don't impress the researchers who have most enthusiastically promoted the primordial soup hypothesis. They've had amino acids in hand for decades. Back in 1953, chemist Stanley L. Miller of the University of California, San Diego shot a streak of electricity through a laboratory mixture of methane, hydrogen, and ammonia--a replica of the primordial atmosphere. This imitation lightning sent chemicals raining down into a flask of oceanlike water below, which grew red and yellow with amino acids in a week's time.

Research has since drawn Miller's hypothetical atmosphere into question, causing many scientists to doubt the relevance of his findings. Recently, scientists have focused on an even more exotic amino acid source: meteorites. Chyba is one of several researchers who have evidence that extraterrestrial amino acids may have hitched a ride to Earth on far-flung space rocks.

Amino acids from a variety of sources almost certainly seasoned a broth on the planet's surface 4 billion years ago, Chyba says, but he points out that no one has ever satisfactorily explained how the widely distributed ingredients linked up into proteins. Presumed conditions of primordial Earth would have driven the amino acids toward lonely isolation. That's one of the strongest reasons that Wachtershauser, Morowitz, and other hydrothermal vent theorists want to move the kitchen to the ocean floor. If the process starts down deep at discrete vents, they say, it can build amino acids--and link them up--right there.