Since the Viking landers' footpads touched down on Mars, scientists have been searching for complex carbon molecules there, which on this planet are the building blocks of all life. They've found some examples in meteorites purported to come from the Red Planet, but debate persists about the origin of those rocks, let alone the carbon signatures inside them, which some have (controversially) argued could indicate life. Now a new study says the rocks in question are from Mars, but the carbon molecules are not relics of extraterrestrial life.