The Allan Hills meteorite (ALH 84001), discovered in Antarctica in 1984, is a sample of the early martian crust. It is about 4.5 billion years old and is thought to have been blasted off of Mars by a meteor impact about 16 million years ago. A possible microfossil, found in a sample of the meteorite, measures less than 1/100th the width of a human hair. This microfossil has caused much debate about whether or not it is evidence for past life on Mars. There is currently not enough evidence to form a conclusion.