Previous missions, notably the Viking landers in the 1970s, have hinted at the presence of organics on Mars.

BBC: Gale Crater: Geological 'sweet shop' awaits Mars rover

The Viking landers took over 7, 000 images of the surface of Mars.

NPR: Revisiting the Viking Missions to Mars

After the Viking landers failed to find life on Mars in 1976, the scientific consensus was one of skepticism that bordered on ridicule.

FORBES: We've Got Company

Thirty-six years after the Viking landers collected soil on Mars, scientists can still make news by declaring that the samples indicate the presence of microbes.

NEWYORKER: The Cosmic Menagerie

Ken Edgett with Malin Space Science Systems, which operates the camera for NASA, compared some of the newest Mars images for the group that gathered last week in Buffalo, New York, with those taken from 1976 to 1980 by the two Viking landers.

CNN: High-resolution images help prepare for Mars landing