Thousands of years ago Mars’ atmosphere was much denser, so it could withstand the effects of the solar wind, as does Earth’s. But a near miss with another celestial body stripped much of that atmosphere, and we’re seeing the results.
That is based on the theory offered in “Worlds in Collision” by Immanuel Velokovsky, written in about 1950. For science buffs it is a great read, tying together a number of historical events to arrive at a most interesting conclusion.
http://www.archive.org/stream/earthupheaval010880mbp/earthupheaval010880mbp_djvu.txt
Immanuel Velikovsky
Earth In Upheaval.
EARTH IN UPHEAVAL is a book about the great
tribulations to which the planet on which we travel
was subjected in prehistorical and historical times. The
pages of this book are transcripts of the testimony of
mute witnesses, the rocks, in the court of celestial
traffic. They testify by their own appearance and by
the encased contents of dead bodies, fossilized skele-
tons. Myriads upon myriads of living creatures came to
life on this ball of rock suspended in nothing and
returned to dust. Many died a natural death, many
were killed in wars between races and species, and
many were entombed alive during great paroxysms of
nature in which land and sea contested in destruction.
Whole tribes of fish that had filled the oceans sud-
denly ceased to exist; of entire species and even genera
of land animals not a single survivor was left.