I had a terrifying dream a few nights ago involving nematodes living deep, deep underground in the hot rocks miles beneath my house. The nightmare was particularly vibrant because I had just learned that such creatures really do live there. For this new knowledge and my subsequent loss of sleep, I blame Marc Kaufman and his new book, “First Contact.” I didn’t think that any beasts, no matter how microscopic, could survive in the Earth’s crust with no contact with the sun-lit world. Apparently, most other scientists didn’t think so either, until Gaetan Borgonie and his colleagues ventured into the extreme depths of South African mines and found them. I’ve never been in a mine so far underground that boreholes gush scalding water, but Kaufman, a Washington Post science writer, got to tag along, and his vivid writing about the hellish conditions no doubt contributed to my wild dreams.

Life underground might seem a strange place to start a book about the expanding new field of astrobiology, but modern astrobiologists are trying not just to find life elsewhere in the universe, but also to chart the extremes to which life on earth can go. Underground? Check. Inside microscopic water bubbles in glaciers? Yes. In arsenic-rich pools? Why not? (In meteorites that fall from the sky? OK, probably not.) Life, as anyone who has ever tried to disinfect his kitchen can testify, is a tenacious thing.

It is no doubt this tenaciousness that leads many of the scientists whom we meet in the book to feel that the existence of life throughout the universe is not just possible, but inevitable. You might be surprised to read, then, that there is no agreement on the answer to what sounds like a simple question: What is life, anyway?

This lack of agreement doesn’t slow scientists down, nor do the setbacks and controversies and arguments that follow anyone who dares to make claims about extraterrestrial life. Kaufman journeys to a telescope high in the mountains of Chile with an astronomer hoping to prove he has found life on Mars, in the form of the methane respired from microbes (many scientists remain skeptical of the data). He revisits the scientists involved in the decade-old claims that there are microbes in Martian meteorites and lets them argue that some of the claims that sounded outrageous 15 years ago are now generally accepted (I will admit: I am less skeptical than I was before); and he treks into the Australian outback with a jazz-loving former chemist who is now one of the premier finders of planets around other stars and who last year dramatically announced the discovery of a “Goldilocks” planet where conditions were just right for liquid water — and thus possibly even life as we know it — to exist on the surface (subsequent observations have failed to confirm the planet’s existence). The range of this new field of astrobiology is exhilarating, and even though scientists are still learning how to sort out the hard science from the understandably infectious enthusiasm, getting to ride along with Kaufman is an expansive joy.

He concludes that our life-finding eureka moment could be just around the corner. I’m less sure, for I know — as Kaufman demonstrates time and time again — that we scientists will argue until our last breath over any data of such monumental import. Still, I’m willing to step back long enough to look at this new field as an enthusiast, rather than a typically skeptical scientist. It’s hard not to become infected by the clear passion and excitement that the search for life beyond the earth brings out. Even in the unlikely event that we end up being all there is in this universe, the insights that we are gaining into our own existence and origins are well worth the loss of sleep that nematode nightmares might cause.

Mike Brown is a professor of planetary astronomy at the California Institute of Technology and the author of “How I Killed Pluto and Why It Had It Coming.”


Scientific Breakthroughs in the Hunt for Life Beyond Earth

By Marc Kaufman

Simon & Schuster. 213 pp. $26