A new glimpse of old life.

A new glimpse of old life

How did life on earth come to be? A new exhibit at the Smithsonian Institution's National Museum of Natural History in Washington, D.C., displays publicly for the first time some of the earliest known traces of life, all of which are helping scientists wrestle with the question of life's origin and development. Shown in the inset is one of the world's oldest fossils, a 3.5-billion-year-old stromatolite from western Australia. The rounded stromatolite mound is thought to have been built, layer upon layer, by communities of blue-green algae or bacteria, which some researchers suspect were capable of photosynthesis (SN: 2/15/86, p. 108). Some scientists think that at the time this stromatolite was formed, the planet may have looked like the painting above--a world dotted with shallow-water stromatolites, wracked by intense volcanic activity and devoid of plants.

What happened between the time of these earliest fossils and the formation of the planet 1 billion years earlier is a matter of much speculation, says the Smithsonian's Kenneth M. Towe, who was chief curator of the exhibit. Included in the displays is the 4.6-million-year-old Murchison meteorite fragment. In this and other meteorites, researchers have found traces of amino acids and other organic compounds, leading some to posit that extraterrestrial bodies brought to earth the basic building blocks of life.

Also included are a few rocks, including a striking gray-and-red-striped "banded iron formation,' that have shaped scientific thinking about the timing and development of the earth's oxygen-rich atmosphere. In addition, the exhibit contains fossil records of life as it began to advance and diversify; on display are remains of single-celled, nucleus-containing creatures that lived 1.3 billion years ago, as well as 570-million-year-old jellyfish and other soft-bodied, multicelled creatures.

Future exhibits may benefit from a recent discovery reported in the June 19 NATURE. Andrew H. Knoll at Harvard University and his co-workers found a rich collection of 700- to 800-million-year-old fossil bacteria, algae and fungi in east Greenland limestones. According to the researchers, the find demonstrates that limestones, which have been poorly explored, are good places to hunt for early microfossils.