Look what they said - conditions would have been very challenging for the last 4 BILLION YEARS.

Four billion years ago the Sol system was still being major-leagued bombarded by space rocks.
The planets were still molten. Heck, wasn't it around that time that Earth got hit by that huge
space rock that eventually created the Moon? I doubt conditions on Mars were very Earthlike
at all. Or maybe they were, but Earth 4 billion years ago was anything but life friendly.

And the words they use - very challenging. That's almost a PC term for Unless you are one
of those microbes that can survive without water and sunlight and take levels of radiation
that would fry more complex creatures in a second, life didn't have a chance on Mars.

We are still thinking (wishing) about Mars as it was in the pre-Viking/post-Canals days.
If there is any life on the Red Planet, it has to be buried very deep, where we won't find
it until we start having human colonies there. We won't find it by scratching the surface
as we have been and will be on the next few upcoming missions.

Yes, Mars is a fascinating place in its own right, but if we want to find any kind of life -
especially in our lifetimes -we need to get past the Mars paradigm and start checking
out places that have major league abundances of liquid water, like a certain moon
around a certain giant gas planet.