The Case of ALH84001

Have signatures of alien life arrived on Earth?

Astronomers think comets and asteroids made consistent collisions with Earth up until about 3.9 billion years ago. They brought carbon compounds and water, possibly leading to the formation of our oceans. But ALH84001 brought something extraordinary in its own way. Image by NASA.

It’s December 1984 and the Antarctic landscape is a glimmering, slippery expanse in the sun. Raucous winds mold the ground into ripples, ice appearing as soft and shiny as wax despite its true hardness. Cracks in its surface can be as deep as 600 feet. Daisy-white graves for anyone that falls inside. The cold needles its way into the crevices of jacket sleeves and flushes the researchers’ skin as they huddle beneath heavy scarves and gloves and fresh powder from their expedition. It’s a stark and unforgiving world. But these are also the best conditions in which to find meteorites, nestled at the base of mountain ranges and preserved in sheets of old blue ice. The blue ice is exposed when the newer layers above are eaten away by scraping winds. It pushes against the tents where the scientists work. This occasion is proving to be special.

The meteorite found in the Allan Hills region, at the edges of the continent and on the cusp of the Southern Ocean, weighs nearly 5 pounds (2 kg) and bears traces of fusion crust — a dark glassy texture formed when the rock cut a burning path through the Earth’s atmosphere. Once landed it was preserved for 13,000 years in the protective low temperatures. Some researchers believe the rock looks green from the inside, though the color is duller when it’s properly at the…