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Evidence of arsenic-breathing life has been discovered by researchers in oxygen-starved waters while working off the coast of Mexico. These resilient microbes, aside from being a vestige of the ancient past of the Earth, could be a sign of the influence the climate change has on our planet’s waters.

When the Earth was just in its youth, billions of years ago, there was not an abundance of oxygen that the first organisms to emerge could enjoy. Instead, these pioneering microbes got their energy from other elements such as sulfur, nitrogen, and even arsenic which is known to be a poisonous compound. After some more time passed, our planet became rich in oxygen and organisms began photosynthesizing and converting carbon dioxide into oxygen.

Scientists used to think that those early microorganisms were made obsolete by generous amounts of oxygen, but this week new research has been published in Proceedings of the National Academy of Sciences says that there are still some organisms with an arsenic-based respiratory system and their location is quite self-explanatory, they live in low-oxygen environments.

The Pacific Ocean is home to some Arsenic-Breathing Microbial Life

Their favorite places include marine oxygen-deficient zones (ODZs) which are a middle layer of the tropical ocean where there are extremely small amounts of oxygen, only traces of it. A team along with their leader, Jaclyn Saunders, a postdoctoral fellow at the Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology, discovered these atavistic microbes off the coast of Mexico in the Eastern Tropical South Pacific ODZ.

“We’ve known for a long time that there are very low levels of arsenic in the ocean,” Gabrielle Rocap, a co-author of the study and a University of Washington professor of oceanography, said in a press statement. “But the idea that organisms could be using arsenic to make a living—it’s a whole new metabolism for the open ocean.”