All the interest in NASA’s search for life on Mars led me to revisit old favorites.

People who want to write about life on other planets instead write about life on Earth. It’s the only life we know. These two books share the same information sources but the authors have very different perspectives.

What you’ll find
Rare Earth presents the paradox that microbial life may be nearly everywhere but complex life almost nowhere. While some exobiologists assume Earth is an average, typical world, Rare Earth shows how unusual Earth is. The Sun’s uncommon richness in heavy elements, the narrow habitable zone in space, our oddly large moon, and the unexpected role of plate tectonics make Earth a rare planet in a rare position.

Fierce volcanic ocean vents are supplanting the idea of gentle pools of prebiotic soup as the site where life began. Current thinking on global catastrophes from Snowball Earth to the giant meteor that destroyed the dinosaurs makes life’s persistence seem remarkably lucky.

Ward and Brownlee present the rich controversy in this active and far-ranging science. They explore lines of evidence and important clues that lead to competing theories. Their prose conveys the uncertainty without awkward phrasing. It is a wonderful book to read.

Rare Earth ends with a chapter assessing the famous Drake Equation. Captured opens with the creators of that equation, Frank Drake and science’s gatekeeper for wild ideas, Carl Sagan. We meet an array of people including NASA’s controversial administrator, the Mars Society (founded in Boulder), and UFO fans. These strong, flamboyant characters are obsessed with the thought of intelligent life on other worlds. How they go about designing laser-powered space ships, imaging the pareidolidal Face-on-Mars, searching for planets around distant stars (today found!), and arguing over the constraints on life makes interesting reading.

Same and different
You will learn more about science from Rare Earth and more about people from Captured by Aliens. From the number of words I wrote, I guess I like Rare Earth better. But both books draw the same conclusion. “To us, … it appears that Earth indeed may be extraordinarily rare.” [W&B] “You start adding these things together and you get a bit of a chill, an omen of present and future loneliness.” [A]

What Amazon says
These books are over a decade old – I could only find print versions on Amazon – so the details are out of date. They have fared quite differently over the years. Rare Earth is highly rated with many reviews and a high “Best Sellers Rank” on Amazon. Captured by Aliens is also rated highly but by fewer reviewers, with a modest sellers rank.