Final answer:
The Viking landers, launched in the 1970s, were sent to Mars with the principal goal of searching for evidence of life. They carried out complex experiments but found no conclusive proof of life, only chemical activity in the soil.
Step-by-step explanation:
One of the principal goals of the Viking landers in the 1970s was to search for life on Mars. The Viking 1 lander touched down on the surface of Chryse Planitia on Mars on July 20, 1976, followed by Viking 2 in Utopia Planitia. These missions aimed to photograph the Martian surface and carry out complex experiments to search for evidence of life. Despite the sophisticated equipment and experiments designed to detect biological activity and organic molecules, no conclusive evidence of life was found. The soil tests indicated some activity, but this was attributed to chemical reactions rather than biological processes, suggesting that Martian soil is chemically active due to its exposure to solar ultraviolet radiation.