  An origin of Earth life on Mars would resolve significant inconsistencies
between the inferred history of life and Earth's geologic history. Life as we
know it utilizes amino acids, nucleic acids, and lipids for the metabolic,
informational, and compartment-forming subsystems of a cell. Such building
blocks may have formed simultaneously from cyanosulfidic chemical precursors in
a planetary surface scenario involving ultraviolet light, wet-dry cycling, and
volcanism. However, early Earth was a water world, and the timing of the rise
of oxygen on Earth is inconsistent with final fixation of the genetic code in
response to oxidative stress. A cyanosulfidic origin of life could have taken
place on Mars via photoredox chemistry, facilitated by orders of magnitude more
sub-aerial crust than early Earth, and an earlier transition to oxidative
conditions. Meteoritic bombardment may have generated transient habitable
environments and ejected and transferred life to Earth. The Mars 2020
Perseverance Rover offers an unprecedented opportunity to confirm or refute
evidence consistent with a cyanosulfidic origin of life on Mars, search for
evidence of ancient life, and constrain the evolution of Mars' oxidation state
over time. We should seek to prove or refute a Martian origin for life on Earth
alongside other possibilities.
