"Other images show the "sphericals" as being hollow and easily crushed by the treads, and having stalks, and growing together."

This is an example of "proving too much". If Mars had plant life developed to the point of having stalks and visibly growing in macroscopic amounts over this time frame, we wouldn't be "debating" life on Mars because it would be plainly obvious that it has life, if life was that active.

This is why we discuss whether or not it has a micro-organism based ecology that it is hiding, rather than discussing whether or not it has forests that we just haven't found yet.

I've noticed this is one of the key signs you can use to identify cranks massively overfitting data about life being here or there.

Fungi (and lichen) is known to be able to survive in places where plants cannot. So it's entirely possible that fungi could survive on Mars while trees/moss/grass could not. We also know where this happens on Earth[1][2]. We didn't discover these life forms from orbit or even by standing and looking at them.

[1]: https://en.wikipedia.org/wiki/Biological_soil_crust [2]: https://www.wbur.org/hereandnow/2021/02/15/antarctic-ice-new...

> So it's entirely possible that fungi could survive on Mars while trees/moss/grass could not

Nope, there is no real chance to find fungi living at -50C to -70C, with no liquid water. There is no life on Earth that lives at such low temperatures, and there is no way for life as we know it to work without liquid water (or perhaps other liquid solvents, though that is highly speculative).

Also note, fungi in particular can't deal with extreme cold, the coldest I've read about any kinds of fungi living is ~0C. There are bacteria and other prokaryotes that survive at temperatures below that, but even then only at high pressures that allow liquid water to exist at very low temperatures - whereas Mars has extremely low pressure, much lower than anyone on the Earth's surface (Martian atmospheric pressure is comparable to Earth's upper atmosphere).

Whether life could survive is entirely orthogonal to my point, and sneaky life surviving that we can't even see is exactly what I said could still be on Mars. What can't be on Mars is life with stalks (it may not sound like much to a Earth-bound human in 2021, but that's actually quite sophisticated for life) that grows macroscopically over the course of just a few days. There'd be evidence of their metabolites, probably color and spectra changes like Earth's greenness as something uses sunlight, all kinds of things. Macroscopic plants are way too much to claim on the basis of a few photos. I mean, if nothing else, we ought to see lots of them.

I assume you're referring to Fig 31. (I was referring to Fig 32)

"Spherical" clumps of blue dust would crush just the same. Mars is reeeeally cold a lot of the time and has a bit less gravity. Dust can clump. Again, not a geologist.

What's important to me is that they're presenting crossing tracks as evidence of before/after, when it's not. They don't have two images of the same area separated by X days, they have one image of two tracks separated by X days, and are interpreting the crest-clumping as "new". This is a somewhat disingenuous way to present, if I'm reading it right.

I'm into sending a robot to grab some, don't get me wrong, but I'm also not privy to all the details to make an intelligent prioritization of the robots' time.

> the rest of the evidence really pushes towards organic growth as the most likely scenario

We know next to nothing about geological processes that can happen at low temperatures and extremely low air pressure. Biological explanations are never 'the simplest', as there is no kind of geological formation that comes even close to the complexity of a single cell, nevermind the complexity of a multicellular organism.