Two essential questions about life in the Universe

How did life on Earth begin? Is there life on other worlds? These two questions have an excellent pedigree as human beings have been asking them for a very long time. What is remarkable about this historical moment, however, is how close we may be to answering either one. Even more remarkable, given their importance, is how an answer to either of these momentous questions will reflect heavily on the other. 

Is Earth Exceptional is a new book that deliberately takes on these two questions at once: the origin of life on Earth and the search for life beyond Earth. The pairing of the issues into a single linked set of explorations is not a conceit or a clever form of packaging. Written by astrophysicist Mario Livio and biochemist Jack Szostak, what this important new book offers is a deep dive into the rapidly advancing science associated with each question — and an equally deep mediation on how they each play off each other.

Is Earth exceptional?

Early on in the book, Livio and Szostak introduce the all-important “ZOI principle,” which stands for Zero-One-Infinity. At the heart of our questions about life in the Universe is a basic question about probabilities: How likely is it to get life started on a random planet where the conditions don’t exclude its emergence (conditions like having no atmosphere or being too hot or too cold)? If the basic material building blocks for life are present, then what is the probability that what happened on Earth some 3.5 to 4 billion years ago will happen elsewhere? 

The Z part of the ZOI principle stands for Zero. Is it possible that what happened on Earth was, essentially, a one-off? Was it a cosmic accident with a probability of, essentially, zero? That would mean the origin of life never occurs anywhere else. People who don’t study the problem often balk at this possibility. After all, there are so many potentially habitable planets in the Universe, (the number is thought to be 10 billion trillion), so surely what happened here must have happened elsewhere. The problem with this reasoning is it assumes that 10 billion trillion is a large number. However, numbers are only large relative to other numbers. If the odds of forming life on a randomly chosen and potentially habitable planet are less than one in 10 billion trillion, then the Universe simply runs out of planets. The Earth will be spectacularly unique because our planet just got spectacularly lucky. 

The important thing to recognize is that, as of today, we have no scientific idea what the odds should be of forming life on a randomly chosen potentially habitable planet. In other words, we don’t know what value nature has chosen for that probability. If, however, we could scientifically answer the question of how life formed on Earth, that would take us a long way toward knowing a universal probability for life’s origin. Half of the book focuses on this question of terrestrial origins. This is Szostak’s domain of expertise. A Nobel Prize-winning biologist, Szostak’s current research focuses on the origin of life as well as the creation of artificial life. He is the expert to talk with if you want to know how “accidental” the formation of life might have been. 

Then, however, there is the OI, or “One-Infinity,” part of the ZOI principle. This is the idea that if you found just one other independent example of life in the Universe beyond Earth, you could reasonably say there must be many others out there beyond your single discovery. Finding just one planet with “alien” life would, in other words, be enough to assume our Universe is teeming with alien life. 

So, how close are we to finding alien life? This is Mario Livio’s domain. A theoretical astrophysicist of wide-ranging interests and immense talent, Livio is the expert to talk with if you want to know about the science of astrobiology and its search for life on other worlds.

This pairing of Szostak and Livio and their particular specialties makes Is Earth Exceptional such a joy to read. It takes the reader deep into the frontiers of both the origin of terrestrial life and the astrobiological hunt for extra-terrestrial life. It’s not just that reading this book will teach you the where, what, and how of science on the front lines of these critical questions (it will!). Instead, it’s the insight the book gives on why these two questions together represent different faces of an ancient quest to understand our place on Earth and beyond it.