hi

Present conditions on Mars do not favor the existence of life. For one thing, modern Mars has no significant global magnetic field and an extremely thin atmosphere, so bombardment by cosmic rays is likely more severe than on Earth. (It’s been mentioned as one of the hazards to human exploration of Mars.)

If it was ever present, how far Martian life spread out in time and across the planet depends on how long conditions favoring its survival lasted. If life was localized rather than widespread, there would be no traces in most soils or bedrock. The term “bedrock” does not imply any great age. On Mars, much bedrock is likely to be volcanic lava eruptions since the time that life is mostly likely to have been present. Older bedrock may be exposed on Mars but only in cliffsides which rovers cannot sample. Large natural exposures of old rocks on Earth are mostly the result of active tectonics and erosion. Mars seems deficient in the right kinds of both of these.

Even on Earth, where conditions favor life, the rock record is not rife with fossils until about 600 million years ago or so (beginning of the last 13% or so of Earth’s history) and much of what has been found was found only recently in a few places in the form of possible microscopic cells. Stromatolites, structures produced by microscopic lifeforms even today, have been found in very old Earth rocks but I doubt if Mars rovers are equipped to search for either cells or stromatolites.

Even with all that, Martian life is still worth looking for. Humans spend a lot more effort and money on much more trivial things than that.

Some informed, imaginative musings are in order.

Exactly.

I think the clincher nay cone from isotope chemistry.