PSU Magazine Spring 2000

A microscopic photograph of heat– loving bacteria. playing field, making their detection work simpler than in other places. These environments are also where scientists are likely to find the types of microorganisms that lived at the dawn of life. Evidence suggests that life may have originated at high temperatures at chemical extremes-in environ– ments similar to the deep-sea hydrothermic vents where these scien– tists get their samples, Cady explains. Others argue that life may have evolved at cooler temperatures. In either case, the period of intense meteor bombardment early in Earth's history probably extinguished life several times, says Cady. The only survivors of this period may have been the high temper– ature microbes that lived in vents in the deepest water-the only water that was left after the oceans were vaporized from the high impact. T heories abound about the beginnings of life. But most of them point to the high probability that the microbes living near the deep-sea vents or in other harsh envi– ronments are life's earliest ancestors. These early life forms got their energy through chemical reactions-a process called chemosynthesis-eons before the photosynthesis used by modem plants. The microbes in the hot pools at Yellowstone use that very process, giving hints to their ancestry. Both Reysenbach's and Cady's work take them to Yellowstone National Park, which, fortunately for them, holds the dual attraction of being one of the richest sources of chemosyn~ PHOTO BY ANNA-LOUISE REYSENBACH