With TV cameras pointed at her, Felisa Wolfe-Simon began speaking at NASA Headquarters in Washington, D.C., on Dec. 2, 2010.

“I’ve discovered — I’ve led a team that has discovered — something that I’ve been thinking about for many years,” Dr. Wolfe-Simon said. She was at that time a visiting researcher with the U.S. Geological Survey, speaking to a sizable audience of journalists and bloggers, two of them wearing tinfoil hats, and hordes of streamers online.

Days before, NASA had teased “an astrobiology finding that will impact the search for evidence of extraterrestrial life.” Speculation that NASA had discovered some kind of alien life bred exponentially across nascent social media platforms.

Dr. Wolfe-Simon had, unfortunately, not found aliens, nor had she ever said she did. But she had found a terrestrial organism that was behaving unlike any life form known on Earth.

The creature came from the mud of Mono Lake, a body of water near Yosemite National Park that is nearly three times as salty as the Pacific Ocean. The lake has the pH level of glass cleaner and, most importantly for her team’s discovery, is full of toxic arsenic.

All known living things use six major chemical elements to keep their bodies churning. One is phosphorus. But from Mono Lake, Dr. Wolfe-Simon’s team said they had isolated an organism that could replace phosphorus with arsenic.