Most scientists who study the origin of life assume that it occurred in the ocean. But a minority view is that ions in seawater may interfere with prebiotic chemistry, making a freshwater environment more likely.

“The main argument for a marine origin is that there is so much seawater,” says David Deamer of UC Santa Cruz. Roughly 98% of the Earth’s water bodies are salty, and this percentage was likely much higher 4 billion years ago when we think the first life-forms made their appearance.

But Deamer doesn’t think quantity is a substitute for quality. Seawater, in his estimation, is too reactive with certain biomolecules to have served as the “broth” for the primordial soup.

Deamer and his colleagues are testing this idea by studying several geothermally heated “ponds” around the world to see if they can’t cook up some of the more complex molecules of life in these freshwater environments. Deamer recounts these adventures in a new book called “First Life: Discovering the Connections between Stars, Cells, and How Life Began.”