This graph shows the abundances of some elements and isotopes in the martian atmosphere compared to the same elements and isotopes in the martian meteorite EETA 79001. The martian atmosphere was measured, on Mars, by the Viking lander spacecraft in 1976. The gas in the martian meteorite was measured in laboratories on Earth. If the two gas samples were identical, points on the graph would fall on the straight line from lower left to upper right. As you can see, the gas from the martian meteorite is identical to the martian atmosphere.