Phys.org [phys.org]:
If you could borrow H.G. Wells' time machine and travel back three billion years, it would take your breath away, literally. There was no oxygen in the air. You wouldn't be able to breathe.
"The Earth was as alien as another planet, with no oxygen in the atmosphere, acid oceans and high levels of toxic elements like arsenic," said researcher Barry Rosen, a Distinguished Professor at the FIU Herbert Wertheim College of Medicine and a world-renowned expert on arsenic. "The first organisms had to evolve ways to detoxify arsenic to survive in that hostile environment."
Those organisms developed arsenic resistance genes that had genetic information for transport systems that pumped arsenic out of the cells and for enzymes that transformed arsenic into more complex molecules.
The research has implications for human exposure to arsenic in groundwater.