An Ancient Building Block of Life

Behold a piece from the Tagish Lake meteorite fall of January 2000. The fragments — one of which seen here still encased in a chunk of ice — represent one of the oldest and most pristine samples of the early solar system.
Alan Hildebrand (University of Calgary)

Astronomers have long assumed that organic molecules — compounds fundamental to life — were among the primary components available to build the solar system. Now they have physical evidence to support this idea. The smoking gun comes from measurements of the famed Tagish Lake meteorite. The bolide, whose fragments fell to Earth on January 18, 2000, landed on a frozen lake in northwestern Canada. It represents one of the most pristine meteorite samples ever collected. Since the rock's fragments stayed frozen and were barely exposed to the terrestrial environment before they were collected, the pieces are chock-full of volatile (easily vaporized) compounds that date back to ancient times.

How ancient? A team headed by Keiko Nakamura-Messenger and Scott Messenger (NASA/Johnson Space Center) analyzed organic globules within the sample and found them to be more than 4.5 billion years old — hundreds of millions of years older than the most ancient terrestrial rocks. What's more, the globules inside the rocks likely predate our solar system and formed either in the outermost reaches of the protosolar disk or in a cold molecular cloud. "These organic grains are still intact in the meteorite, which means that we have direct samples of organic materials that formed in a distant cosmic environment before the planets did," says Messenger.