IS EARTH EXCEPTIONAL?

What is life, and where, besides earth, might it exist?

Bestselling author and astrophysicist Livio and Nobel Prize–winning professor of chemistry at the University of Chicago Szostak admit that neither question has yet been answered, but they assert that recent decades have seen spectacular advances. They ask: Did life develop through a freak chemical accident, or is it inevitable under the right conditions? As long as life exists on only a single planet, the answer remains speculation, but discovering a second example would open the floodgates to a universe teeming with life. Unlike other universal goals (world peace, a cure for cancer), this one seems on the verge of being achievable. Researchers have demonstrated that simple compounds present on the early Earth can trigger chemical reactions that produce building blocks of the earliest protocells: nucleic acids for their genes, amino acids for their proteins, lipids for their cell walls. The authors’ warning that “there is quite a bit of chemistry involved” is no exaggeration; they proceed with details of processes, reactions, and molecular structures that may flummox readers who are unfamiliar with college biochemistry and may breathe a sigh of relief when they reach Chapter 7 (halfway through the main text) and the focus changes to astronomy. In searching for life in our solar system, Mars and Venus have proved a disappointment, but promising water oceans exist on moons of Jupiter and Saturn, and Saturn’s largest moon, Titan, has a thick atmosphere as well as rivers, rain, and seas, although they’re of liquid methane, not water. From the first planet discovered around a distant star 29 years ago, the number has grown into thousands, and Earthlike planets make up a significant fraction. Livio and Szostak conclude that, to date, hard evidence of alien life hasn’t appeared, but they deliver a compelling account of what would constitute proof. Everyone has high hopes for the next generation of probes and telescopes.

The latest on a fascinating search.