Ancient life on Mars?

In short, they have never before seen anything like that body, nor any analogous life-form.

What are some of the methods that might be used to identify the body as a dead creature, as opposed to some accidental planetary formation? There is probably no single criterion, no touchstone that can provide an answer. Rather, a combination of factors is likely to be indicative, even if proof might be impossible. Here are some questions that might be asked.

How does the body relate to its surroundings? Is it demarcated from the surrounding material by some discontinuities? We need to have a good idea of extent and limits of the body if we are to be able to analyze its characteristics.

What is the body’s scale relative to the creatures performing the analysis? If the body were millions of times larger or smaller, it might not be recognized as a body. These first two questions relate to the issue of what scope of a system can be considered as alive. Is a DNA molecule alive? A virus? How about a planet, such as Earth?

How complex is the structure of the body? Is it composed of identifiable sub-structures, themselves of a certain level of complexity? Can the body be distinguished, for example, from a mineral crystal? Crystals might be orderly and distinct from the matrix in which they are embedded, but are they ever alive?

Is there reason to believe that the body was a component in a sustainable eco-system, even if that eco-system is itself dead? For example, if you find a dead jellyfish floating in the ocean with the remains of partially digested fish inside and the same fish swimming around it, you have clear evidence that the jellyfish could eat, a key characteristic of life. But if you find that same jellyfish in the middle of a desert, you might wonder if such a structure could have ever survived in such a place. Of course, a waterspout might have picked it up and somehow deposited it elsewhere, but such hypotheses render the conclusion many orders of magnitude less likely. But, what if we discover traces of water frozen underground and fish skeletons near the jellyfish. Now we have traces of an ancient eco-system, making the supposition of life less fantastic. This same approach is used when coprolites are related to the dinosaurs that presumably produced them.

However we define life, a creature must have a means of absorbing and using energy. Do the structures of the body support a hypothesis for how that energy might have been used in a way different from a simple physical process? For example, the action of sunlight on a puddle might result in its evaporation, but we would hardly call the puddle alive. Suppose, though, we find a canteen containing one liquid near one opening of canal that traverses the creature’s body, and the remains of another liquid, with a different chemical composition, near the other opening of that canal. Might not this be evidence of complex processing of the ingested liquid?

Has the surrounding of the body been disturbed or transformed in a way that natural processes could not easily explain? Even the simplest organisms with which we are familiar affect their environment. An unusual distribution of bacteria might be the result of the presence of penicillium. Our paleontologist might find a series of holes in the ground near the body. Are they randomly distributed, perhaps due to karstic erosion, or are they equally spaced in a circle, suggesting that the body had built a shelter, now long disappeared? Can we confuse the pyramidal mountains whose form is due to the natural splitting of rock or the erosion from wind-borne particles, with the structures built in Egypt by the pharaohs over 4’000 years ago?

Is it possible to reanimate the body? A few jolts of lightning, à la Frankenstein, and we see for ourselves that the body, once alive, has come to life again. Alas, what about those molecules in the primordial soup, also struck by lightning? If this indeed was the origin of life on Earth, then (re-)animation is not, by itself, a definitive indicator of life.