Sciency Words: Preservation Bias

Hello, friends!  Welcome back to Sciency Words, a special series here on Planet Pailly where we take a closer look at interesting and new scientific terms in order to expand our scientific vocabularies together!  Today’s Sciency Word is:


So is there life on Mars?  Well, there could be.  It’s not totally impossible.  But as I’ve said before on this blog, I think the odds of us finding living things on Mars are pretty low.  The odds of us finding dead things on Mars, however… I think those odds are much better!

Or at least I did think that until I read this paper, entitled “A Field Guide to Finding Fossils on Mars.”  That paper introduced me to the concept of “preservation potential,” and subsequent research led me to learn about something paleontologists call “preservation bias.”

Basically, turning into a fossil isn’t easy.  A lot of factors have to come together just right in order for a dead organism to become preserved in the fossil record.  As that Martian fossil field guide explains:

On Earth, most organisms fail to fossilize because their remains are physically destroyed, chemically oxidized or dissolved, digested by their own enzymes, or consumed by other organisms.  Fossilization only occurs when processes of preservation outpace degradation.

Preservation bias refers to the fact that certain organisms—or certain parts of certain organisms—stand a better chance of fossilizing than others.  Preservation bias can also refer to the fact that some environments (rivers and lakes, for example) do a better job creating and preserving fossils than others (for example, deserts).

A lot of factors can get involved in this, but as a quick and easy example, think of the dinosaurs.  Dinosaur bones fossilize easily enough.  Other parts of the dinosaur… not so much.  That, my friends, is preservation bias at work, favoring hard tissue, like bone, over soft tissue, like muscle or fat.

Now imagine what would have happened if dinosaurs somehow evolved without bones (that’s a weird concept, I know, but just bear with me a moment).  How much would we know about those boneless dinosaurs today?  Would we know about them at all?  Those hypothetical boneless dinosaurs could have roamed the earth for billions of years and left hardly a trace of evidence for us modern humans to find!

Which brings us back to Mars.  There was a time, very long ago, when Mars was a much warmer and wetter planet than he is today.  It’s possible—no, I’d say it’s probable!—that life of some kind developed on ancient Mars, just as it did on ancient Earth.  But would that ancient Martian life have left us any fossils to find?  Maybe.  Maybe not.  It depends on the various factors involved in preservation bias.

P.S.: Boneless dinosaurs are delicious.

7 thoughts on “Sciency Words: Preservation Bias

  1. I’ve read stuff before arguing that the Cambrian Explosion was really the skeleton explosion, that there may have been some pretty sophisticated life forms prior to that time, just without skeletons. Of course, it seems difficult for animals to have the mobility they have without the skeletons.

    Adrian Tchaikovsky in Children of Ruin imagines alien animals with hydrostatic skeletons, which probably wouldn’t fossilize. Although given that the wrong kind of injury could deflate a creature’s limb, it seems like the mineralized form we’re used to would be selected over them, if evolution in that biosphere stumbled on it.

    Liked by 1 person

    1. I’ve heard that about the Cambrian explosion too. I remember reading somewhere that paleontologists found some sort of jellyfish-like thing that might have been pre-Cambrian, but I don’t remember the details or even if it was confirmed. The broader point is that it’s plausible: lots of organisms might have been swimming around in pre-Cambrian oceans, and we might never know about them.

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      1. Definitely. And we do know there were animals in the Ediacaran, the geological period prior to the Cambrian. Although the ones that have been found are strange, and seem far less mobile or in possession of distance senses (sight, hearing, smell, etc) than their Cambrian descendants.

        Liked by 1 person

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