It came from Mars and crashed into Antarctica. Its journey from the red planet to the frozen plains was a long one. About 17 million years ago, a monster rock collided with Mars, punching a hole in its side and jettisoning planetary debris across the solar system. The wreckage raced away at more than 3 miles per second, escaping the planet's gravitational pull and fleeing into the cosmos. Then, some 13,000 years ago, a piece of that wreckage landed near a Y-shaped ridge in the Transantarctic Mountains known as Allan Hills. The area, draped in layers of snow, has been dubbed "meteorite heaven" by planetary scientists because the flowing ice sheet of East Antarctica butts up against the mountain range, forming a natural collection area for space rocks.
Cracking open ALH84001 is like opening a portal to a planet more than 140 million miles away. Many research teams had done so since its discovery, but it's NASA geologist David McKay whose name is forever linked to the Martian chunk. McKay had worked on the Apollo moon program, studying lunar dust, and was well-versed in studying samples from other worlds. His team of scientists at Johnson went to work examining ALH84001's chemical components in the early '90s, hoping to reveal what was happening on the red planet 4 billion years ago. In studying the rock, the team uncovered carbonate minerals and unusual, wormlike microstructures within. Over 20 years later, few serious planetary scientists believe ALH84001 contains life from another planet. But the meteorite focused efforts in astrobiology and saw organizations like NASA double down on investigating Mars.
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https://www.cnet.com/science/biology/features/the-antarctic-meteorite-that-changed-our-perception-of-life-in-the-universe-alh84001/
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