Life on Earth

Life on Earth [blank] six basic ingredients - carbon, hydrogen, nitrogen, oxygen, sulphur and phosphorus. Those six elements are the building [blank] for DNA and RNA, along with proteins and fats. Which means they're essential for life - as we know it. But it might be time to update that list. Scientists have found a bacterium that can be done without phosphorus - living on arsenic instead. The researchers had a hunch a bug like this might exist, because arsenic has some chemical properties in common with phosphorus. They collected mud from California's Mono Lake, where the waters are naturally salty and laced with arsenic. Back in the lab, they cultured microbes from that mud. But instead of adding phosphorus to the culture to help the bugs grow, they added varying levels of arsenic. One bacterial strain continued to thrive. And tests [blank] that the organisms compensated for the lack of phosphorus by building their DNA with arsenic instead. The research appears in the journal Science. This is the first known life form that seems to be able to swap [blank] one of life's fundamental building blocks with another element. So for astrobiologists hunting for life in space, don't rule out places filled with poison.