After more than four decades of searching for organic molecules on the surface of Mars, scientists have conclusively found them in mudstones on the lower slopes of Mount Sharp. A variety of organic compounds were discovered by NASA’s Curiosity rover, which heated the Martian rocks to 500° Celsius to release the chemicals.

The finding is significant—for life to have ever existed on Mars there would almost certainly need to be organic molecules to get it started; they’re the basic building blocks of life as we know it. And if life did get started, it would have left organic molecules behind. However the confirmation of organics on Mars raises more questions than it answers. Based upon the information scientists have gleaned so far, they cannot determine whether these organics were produced by life, delivered to the surface of Mars by meteorites, or are the byproduct of geological processes on Mars.

The Viking landers reached the surface of Mars during the summer of 1976 amid some expectation that they might find evidence of past life, if not life itself. However, when Viking landers sampled the Martian soil they found no past life, nor did their gas chromatograph mass spectrometers find any organic molecules. Nada.