In a salty hot spring near Mono Lake, California, researchers have found two new species of bacteria that use arsenic for photosynthesis, and require no oxygen to fuel the process. Researchers say the bacteria may be similar to those that existed on primordial Earth where oxygen was scarce, and may illustrate an important stage of how early life developed in mineral-rich waters over 2 billion years ago.

Arsenic is well-known for its toxicity; it was used so often as tool for homicide in the 1800s that it earned the nickname “king of poisons” [The Scientist]. Yet the newly discovered bacteria can not only tolerate the element, they require it to survive. One of the first steps most organisms perform in photosynthesis is to split water molecules, creating oxygen. Oxygen donates energy in the form of electrons to other molecules, setting off a chain reaction that eventually results in the building of sugars for the organism’s own food. For the red and green bacteria found in Mono Lake, arsenic plays the role of oxygen [Science News].

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Researchers say that diamond fragments from the dawn of time may contain evidence that life began on Earth as early as 4.25 billion years ago, just a few hundred million years after the planet came into existence–although they also say that their findings aren’t conclusive and that they may well be wrong.

Studying anything about the ancient earth is extremely difficult. Rocks that formed four billion years ago will long since have been beat up, metamorphosed, or melted [Nobel Intent blog, Ars Technica]. Researchers got around that problem by studying microscopic diamond pieces inside zircon crystals, which are themselves the tough remnants of ancient rocks that have long since disappeared. “We don’t have the rocks. These zircons are just little fragments of something that was broken up, weathered and redeposited as sediments,” explained [coauthor Martin] Whitehouse [BBC News].

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