Within the past 100--150 years, the conventional wisdom regarding life
in the solar system (beside the Earth) has been on a roller coaster
ride.  Life on other planets used to be considered likely.
Suggestions for sending messages to other planets included cutting
down huge tracts in the Siberian forests or filling and setting afire
trenches of kerosene in the Sahara.  Lowell believed that he could see
evidence for a civilization on Mars.

During the Space Age the planets were explored with robotic craft.
The images and other measurements sent back by these craft convinced
most scientists that only the Earth harbored life.

With even more recent findings, the possibility of life that life
exists or existed elsewhere in the solar system is now being
re-examined.