Wall Street Journal,
April 23, 2011Link
The bottom of a mine shaft doesn't seem like the sort of place a naturalist should go to look for life. But scientists have found thriving communities of microbes living as deep as two miles underground. These organisms can't rely on sunlight for their energy, so they survive instead on the radioactivity of the rocks in which they dwell. They exist in a world separate from our own, an ecological Hades.
As Marc Kaufman explains in First Contact,
these microbes are important for two reasons: They show the extremes to which life on Earth can go, and they can help us imagine what life might look like on other worlds. Mars, for example, was probably a warm, wet planet in its infancy four billion years ago. But then it lost its heat-trapping atmosphere and became cold and dry. If life took hold early on in Martian history, it might have been able to retreat inside the Red Planet. It might still be there today.
In First Contact,
Mr. Kaufman reports on the many different ways in which scientists are investigating the possibility of extraterrestrial life. His research took him to the bottom of South African mine shafts. He traipsed through Death Valley to study puzzling microbial crusts known as desert varnish, which might be another model for extraterrestrial life. He traveled to the Australian outback to see how astronomers hunt for Earth-like planets orbiting other stars. All his research has led Mr. Kaufman, a science writer and national editor at the Washington Post, to a stark conclusion: "Before the end of this century, and perhaps much sooner than that, scientists will determine that life exists elsewhere in the universe," he writes. Not whether life exists, mind you, but that it exists.
Astrobiology is a vibrant field of research these days, and Mr. Kaufman has selected a good group of scientists to profile in his book. Unfortunately, First Contact
reads like a collection of newspaper articles that has not been fully transformed into a book-length narrative. The stories don't unfold--they leap forward, shift without warning and stop for no apparent reason. Some of the scientists Mr. Kaufman profiles speak in transcribed paragraphs. Others say practically nothing. I had a hard time telling who was who, because many scientists seemed interchangeable. One scientist was "tall and thin." Another scientist, a few pages away, was "tall and lanky."
To make the case that extraterrestrial life exists, moreover, Mr. Kaufman tips the balance of the book in favor of scientists who offer favorable evidence. They become maverick, out-of-the-box thinkers, while many scientists who legitimately question those arguments end up looking, when they appear at all, like dark lords of conventional wisdom.
In recent years, for example, a NASA scientist named Michael Mumma has been pointing ground-based telescopes at Mars. In 2009, he and his colleagues presented evidence suggesting that fresh methane was wafting off the surface of the Red Planet--possibly a signature of Martian microbes. This is important research that certainly deserves a place in a book on astrobiology. But Mr. Kaufman casts Mr. Mumma as "a rebel since he was a boy." (I could discern nothing rebellious in his careful work as a scientist.) Meanwhile, Mr. Kaufman gives no serious attention to Mr. Mumma's critics. To name just one example, Kevin Zahnle, another NASA scientist, has argued that the methane Mr. Mumma detected is actually in Earth's own atmosphere.First Contact
also recounts the recent headline-grabbing announcement that NASA-funded scientists had discovered arsenic-based life. All known living things use phosphorus to build the backbone of their DNA. Yet, in December, a team of scientists claimed that they had isolated a strain of bacteria from Mono Lake in California that could use arsenic instead. These bacteria were not aliens. They had evolved here on Earth, adapting to the arsenic-laced water in their lake. What made these arsenic-based organisms important, the scientists argued, was that they widened the chemical possibilities of life, both here and on other planets.
Mr. Kaufman describes the press conference in glowing terms, quoting the arsenic team making grand statements. "We have cracked open the door to what is possible for life elsewhere in the universe," declares team member Felisa Wolf-Simon. Mr. Kaufman acknowledges some critics of the research, but he portrays them as little more than uninformed bloggers.
In fact, the critics were scientists who delivered detailed critiques. Ms. Wolfe-Simon and her colleagues claimed, for example, that the microbes could not be growing on phosphorus because they had removed almost all of it from the experiment. Yet other scientists have found that microbes in the Sargasso Sea can survive on such low concentrations. The critics also pointed out that the experiments could not reveal whether the arsenic was actually incorporated into the DNA or just stuck to it. And in the weeks that followed, other scientists published papers to show just how unstable arsenic-based DNA would actually be.
It is certainly possible that, as Mr. Kaufman asserts, scientists will find life someday on other planets. But I doubt that any of us will live to see it. There's no probe scheduled for launch in the next few decades that's specifically designed to test for the presence of life. Many researchers believe that, on its own, a robotic probe wouldn't be able to distinguish chemical signatures of life, or even fossils, from lifeless geology. We would have to either send astronauts or ship material back to Earth to study in labs. And if life is indeed hiding two miles underground on another planet, chances are that we'll miss it, no matter how hard we scrape the surface.
Copyright 2011 Carl Zimmer