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JohnOwens
2004-Mar-02, 05:05 AM
Something that occurred to me in the wee hours last night:
If there had been life on Mars at one point, but was no longer, would we even see anything resembling what we call fossils here on Earth? After all, the fossilization process involves water, and certain minerals which are slightly soluble in water to be deposited in the organic remains, and a slow but (at least somewhat) steady flow of water containing such a mineral.

So, I'm imagining a sequence of events somewhat like this:
1. Wet Mars, life exists, all is well.
2. Mars starts to dry up, reason unknown.
3. Martian biosphere goes to heck in a handbasket.
4. All life on Mars dies off.

Which brings up questions:
1. Around the time of 4 above, would there be more than the usual number of dead critters around waiting to be fossilized, since any bacteria-analogs responsible for decay would be dead? Or would the bacteria-analogs be the very last to die, with enough time to finish their job about as well as they usually had?
2. If the reason for the die-off had been that Mars was drying up, would there have been enough liquid to create fossils at that point? If there wasn't enough water, is there some other liquid that could serve similarly? Carbon dioxide couldn't possibly do because it would only be solid or gas, pressure being way below its triple point, right? (I'm assuming the pressure wasn't radically higher than at present; I couldn't find the triple point pressure for CO2 quickly online, and my Handbook of Chemistry & Physics is upstairs and I'm not going to bother, but I know it's considerably more than 1 Atm.)
3. If there weren't enough water/liquid for the above, would there have been some other process that would result in something fossil-like being preserved in the rocks? If so, what would they look like, and how different would they appear from what we're used to thinking of as a fossil?
4. On a less speculative note, does anyone know specifics on how they were thinking the might-be-fossil-bacteria in the Martian meteorite were fossilized?

Of course, just about all of this would be irrelevant (assuming a sequence of events similar to mine) as far as any fossils that might have formed before Mars started to dry up would be concerned. So I guess the main question upon which these would have any bearing is whether we'd be seeing any of the fossils from the time life died out, or only from earlier stages in their development.

mike alexander
2004-Mar-02, 06:55 AM
Actually a good question. There are lots of different kinds of fossils.
But as to which era you would be seeing, it would depend to a large extent on chance and geology; which strata have been exposed.

It occured to me that I could head over to the coast here and dig shells out of the exposed sand cliffs that are still fossilizing, go east over the Cascades to dig Cenozoic fossils out of the John Day beds in eastern Oregon, or go another 500 miles and dig 350 million year old horn corals out of the Rocky Mountain Front (actually did that last summer. Very hot, very fun). Depends completely on which beds are exposed.

Staiduk
2004-Mar-16, 02:43 PM
Hi all. :)
I was asked a very good question regarding fossilization via PM; and was directed to this topic.
First; my credentials. You must understand - I have none. My area of interest - palaeontology - and yours - astronomy - both share a great blessing; that is the devout interest of amateurs. In palaeontology, like in astronomy, much of what we know have been discovered by amateurs such as myself. I've found a couple of trackways not previously identified; a few bones, written a few papers, nothing of any signifigance. (Though the one which suggested a reclassification of hadrosaurs generated some talk at my local palaeontology society - 'bout the closest I'll ever get to recognition...thank God. :D )So please understand that everything I say here is based solely on my own opinions, observances and personal instruction.
Anyhoo; to the question. Since we have so much fun watching BA debunk woowoos, I'm going to debunk the question - strictly for fun. :)

1) We have to be careful when we discuss fossilization; there is no 'one thing' - or rather no one method - for creating a fossil. A fossil is described as 'the remains of animals and plants, or the record of their presence, preserved in the rocks of the Earth.' A pretty wide description, I think you'll agree. There are several known ways to create a fossil; each is dependant on its environment.
The first is the way you described; John - Permineralization. This happens most commonly with aquatic life forms (such as crinoid). The Petrified Forest is a stunning, beautiful example of permineralization. It's imortant to remember that with permineralization; although a body's soft parts are gone, the hard bits remain; suspended in the rock. Permineralization occurs when spaces in an organism - such as inside lungs or swim bladders - are filled with mineral-rich water. Over time; as the mineral concentration increases, the minerals precipitate out, taking the structure of the organism; in the same way ice cubes take the structure of the tray.
Another is dissolution and replacement; pretty much one step up from permineralization. In this case; the soft parts are dissolved away (mineral rich water is, by nature, an acid), leaving a hole. The minerals fill this hole and form a cast of the original creature.

Those are the types of fossils most people think of. They require three things in common: 1)that the organism is buried quickly. 2) that the be immersed in mineral-rich water. 3) they need lots of time. There are other ways, however.
Crystallization - In this case the parts - which are usually formed of unstable materials; such as aragonite in clamshells - slowly break down into more stable forms. This destroyed fine detail, but preserves the overall shape. You've undoubtedly seen lovely gypsum shark teeth - that's a good example.
Another type is called carbonization. This occurs when an organism's VOC's (volatile organic compounds) disperse from the body during decay; and end up leaving a thin film of carbon. Best example? You use it every time you drive to work. IOW; hydrocarbons.
Organic trapping. The LaBrea tar pits, and bugs in amber. In these cases; the organisms are kept whole; with the soft body tissues intact.
Don't want to go on too long; just got back from work; and I'll talk all dcday. Suffice it to say; that depending on the type of fossilization; you do not necessarily need either water or bacteria. In fact; you don't want bacteria at all - a sterile environment is best for fossilization.
OK; next point. You said:
So, I'm imagining a sequence of events somewhat like this:
1. Wet Mars, life exists, all is well.
2. Mars starts to dry up, reason unknown.
3. Martian biosphere goes to heck in a handbasket.
4. All life on Mars dies off.

Which brings up questions:
1. Around the time of 4 above, would there be more than the usual number of dead critters around waiting to be fossilized, since any bacteria-analogs responsible for decay would be dead? Or would the bacteria-analogs be the very last to die, with enough time to finish their job about as well as they usually had?

A very, very good question; let me point out that if your sequence (1-4) is correct, it makes one very big assumption - that the death of Mars occured quickly. Very quickly. So quick dead animals don't have time to decay. I know I just said baceria has little place iin fossilization; but there's another form of preservation to consider: mummification. Let's assume (a) a past Mars with a rich biosphere and (b) a quick die-off. So quick that bacteria - or their analogs; as you so excellently put - died off as well. (Terrestrial bacteria are the toughest things on earth. Even cockroaches are fragile compared to the survivability of bacteria.) so what would you see? Not fossils. You'd see mummies. Countless thousands upon thousands of mummies. All you have to do is look at a dead camel in the desert to see what I mean.
(a point occurred to me as I was writing that; I forgot that dead Mars has weather. In it's current state; wind and dust. So much of those left over may indeed be fossilized - metamorphically. But there would still be plenty of mummies left over; in sheltered areas, so the point is still valid. Nyeah, nyeah. :p )
You don't see mummies; you see nothing. So either a)Mars didn't have a rich biosphere or b) the die-off didn't occur quickly. IMO; probably both. I strongly doubt that any life on Mars existed beyond the simple aquatic plant stage. Damnit.
So anyway; I've totally lost track of my original line of argument. ::) The point is; water or no water; there are possibilities for fossilization. Remember; most fossils are found in sedimentary rock; the rest in metamorphic. Mars has a lot of both. If there were life forms on Mars; I'll bet a paycheque there are fossils somewhere. That thing that opportunity destroyed wasn't one of them; nor are the 'blueberries'; but I'm betting they're out there, somewhere.
I hope that helps; I ramble too much.
Cheers!

Kaptain K
2004-Mar-17, 07:34 AM
FWIW - The pressure for the triple point of CO2 is about 5 atmospheres. 8)

Gremalkyn
2004-Mar-17, 07:49 AM
Assume that Martian life can be fossilized. Then, assume we come across such a find. What would be the odds that we would quickly know what we had found? True, the imprint of the life-form against the background material (think shape-against-medium) would indicate the presence of something, but how easy would it be for us to quickly identify a part of a plant from a part of an animal when we would not have a visual reference for the entirity of either? *

Some aspects of biology would probably be similar, but the interplanitary differences in environment would, to some extent, create different aspects in the Martian development.

Ex: A fern from Earth looks like a fern because it developed here, under our gravity and under our (evolving) climate. What would a Martian "fern" look like, and how would we know it *was* a fern if all we had was part of the first fossil?

* How would we know that what we have found is part of a multi-articulated plant frond and not part of the webbing from an aquatic/amphibian animal? If the plant has stems like bamboo, how would we know the fossil was the fern and not finger bones?

Kaptain K
2004-Mar-17, 10:09 AM
True, the imprint of the life-form against the background material (think shape-against-medium) would indicate the presence of something, but how easy would it be for us to quickly identify a part of a plant from a part of an animal when we would not have a visual reference for the entirity of either?
How would we know it was the imprint of a life-form? Assuming that there was life on Mars at one time, we don't even know what it looked like. We identify fossils on Earth by their resemblance to life-forms we already know about. Either by their direct resemblance to living creatures, or by a concatination from current life back through a chain of fossils.

Gremalkyn
2004-Mar-17, 10:33 AM
I think I am not being clear. Part of that is due to my lack of specific scientific training and the fact that I have not had any "schooling" for over 10 years now (my geology class, specifially, here). Let me also say that, regardless of what the fossil was, it would be a wonderful find.

Quote: "We identify fossils on Earth by their resemblance to life-forms we already know about. Either by their direct resemblance to living creatures, or by a concatination from current life back through a chain of fossils."

My point exactly. How would we know what the thing was if this was (one of) the first fossil(s) of the Martian life-form? We could theorize that a Martian fern was a fern because it looked like an Earth fern, but we would not know for sure until, as you say, above.

My example of the fern and the amphibian may need a bit of work. Assume the fossil depicted three mostly straight "pencils" with two connected segments each, with some sort of material between the "pencils." How would we, way back here on Earth, know if the life-form fossilized was:

1) a plant, where the "pencils" are veins for conducting nutrients and the other material was the light-gathering portion, or,

2) an animal, where the "pencils" are the bones and the other material is some sort of webbing between those bones?

Gremalkyn
2004-Mar-17, 11:02 AM
Perhaps I should just restate the question.

Assume the rover (pick one) finds a fossil and studies it to the best of its ability. Regardless of it being plant or animal remains, can the rover's equipment sufficiently differentiate between "rock" and "fossilized organic," or would we have to primarily rely on the visuals provided by the cameras to know it had found a fossil?

Kaptain K
2004-Mar-17, 11:22 AM
I don't think you understand what I was trying to say. I believe that all we can say is that we have found an anomalous rock formation that "might" be a fossil. We don't know that Mars ever had life and if it did, we have no idea what it looked like. Speculating as to whether it is a fern or an amphibian is pointless as long as there is a strong probability that it is nothing more than an unusual rock!

Gremalkyn
2004-Mar-17, 11:26 AM
I understood your direction, just not your point of origin; I got what you were saying, just not why you said it as you did.

Got it now, though.

Staiduk
2004-Mar-17, 12:57 PM
Eek; a tough question - way beyond my ability to even speculate.
Still; I personally believe that life evolves using the path of least resistance; so to speak. It finds the simplest solutions; and goes with it. For all the incredible complexity and diversity of life on Earth; each life-form;s individual mutations (individual to a species that is) represents the simplest answers to that species' needs.
Not very helpful; I'll admit.
Still; while we may have no idea what kind of fossil we find; I personally have a suspicion that should we find one; we'll probably know about it. Take plants, for instance. Your average ground plant has two characteristics: It's green and leafy. Green; because it uses Chlorophyll for photosynthesis. Leafy; because the leaves are solar collectors/food factories for the plant. As insanely complex as plants are; (and a simple leaf is not simple; it's an amazing piece of evoultion) they are the simplest they can possibly be; or rather no more complex than they have to be. So I'm willing to theorize that if we did find the remains of a martian plant it would likely have leaves of some description - assuming of course that Martian life evolved to that level.
Thre's no scientific means to back that statement up; just belief. So; I think that were we to see a fossil; we would probably recognize it as such. Just what the dead thing was would be another matter; and surely a ripe topic for another round of debunking on this site! LOL!

Kaptain K
2004-Mar-18, 08:10 AM
Life does not "choose the simplest solution". It "tries lots of solutions". Those that work, reproduce. Those that don't, don't. Those that work better than others reproduce more and eventually drive the less successful out.

Staiduk
2004-Mar-19, 05:10 AM
Well yes; but that's a different aspect. As organisms adapt to meet their environment; the successful adaptations will succeed while the unsuccessful die. But each time an organism adapts; that adaptation will be the simplest possible adptation that solves the problem.
for example; let's consider a ground-dwelling leaf-eater. It is in competition for all the leaves it can reach with all the other leaf eaters. Ultimately; this creature's decendants may become giraffes; but for now; it's immediate offspring may have slightly longer front claws that give it an advantage in hooking down the higher branches. Or it might learn to stand on its hind legs. Whichever works; the simplest, smallest adaption that will correct the problem. So when our hypothetical leaf-eater has kids, it isn't going to suddenly pop out a girraffe; comical as that might be to watch. :D

RBG
2004-Mar-19, 07:06 AM
On the other hand,

maybe some very specific & extremely, extremely rare sets of complex circumstances are needed before life can kick-start and Mars has always been as sterile as our moon.

Ok, pretend I didn't write that.

RBG

Kaptain K
2004-Mar-19, 09:14 AM
But each time an organism adapts; that adaptation will be the simplest possible adptation that solves the problem.
Not necessarily! The adaptation that works, simple or complex, is the one that will be adopted. Mutation is blind. Evolution is not goal-directed. It is results-directed. Whatever works, works. The simplicity or complexity of the solution is irrelevent. Of all the possible solutions, the one(s) that are most efficient succeed better than those that are less so. That is all that matters.

eburacum45
2004-Mar-19, 10:44 AM
Absolutely; evolution very often does not produce the simplest solution for a given environment; the remarkable and baroque diversity of the Earth's environment is a testimony to that.

Martian fossils might well be difficult to classify as to their function; consider the early Earth fossils in the Ediacaran assemblage; flattened disks, fronds, stalks and leaf like forms; particularly the Vendian fossils (whatever they are)
it is not possible to easily determine if these were animals plants or some but the Vendian fossils can be identified as fossils per se because of the degree of organisation they display.

--------
Another problem is the corrosive nature of the environment as the water on Mars escaped to space or froze into the soil; the water will have been exceedingly salty, or acidic, or both; fossils are difficult to find in evaporite deposits but not impossible...
I doubt if any rover vehicle will be likely to find such problematic remains.otherwise unknown kingdom of lifeforms (the Vendazoa)
http://www.fact-index.com/v/ve/vendian_faunas.html


But a team of human geologists probably could, if they are there.

Staiduk
2004-Mar-19, 01:18 PM
Once again; I agree with everything said. The trouble may be in my definition of the term 'simple'.
Briefly; an adaptation takes place by modifying something already existing on the organism at the time; it doesn't 'invent' something totally new. Feathers, for instance; didn't appear overnight; they're adaptations of an already existing body structure - scales.
I'll try to describe my opinion (and remember; the simple argument is my opinion; nothing more) this way:
Let's look at an imaginary creature I'll call a 'Sea Beaver'. (We'll use a pretend animal to avoid comparison with real ones.) Sea Beavers live in the sea reasonably close to shore; feeding on fish and shellfish. They're a little over two meters long; fully aquatic. They have a powerful vertically fluked tail for swimming; with fore and aft flippers for control. They have lovely glossy dark brown pelts. Now; let's look at the creature Sea Beavers evolved from.
(Hop in the DeLorean; get up to 88...boom!)
OK; here we are about 2 million years earlier. We're about five kilometers inland from the water; it's a lush rainforest where insects, ground vegetation and small mammals are abundant. Now - look under that fern there - see it? That's another imaginary creature I'll call a woodhog. Woodhogs are about a meter long; low, badger-like creatures. They're omnivores and scavengers; anthills are a favourite food source. We're looking at a small family group of five males; seven females and a few pups. Aside from stripes in the coats; there's very little to distinguish them - except for one. That male in the back - call him Male 1 - has a problem - Woodhogs' front claws are large and strong; for ripping into wood to get at the grubs. His claws are too big, however. He has trouble walking due to the claws' impedance. He's young - about two years; but he's not likely to see three with such a disability - it's a simple mutation that will ultimately kill him from starvation, predation or conflict.
This particular family of woodhogs have ambled their way down to the shore; and begun experimenting with the local restaurants - which serve sushi. They find it quite to their liking; and stay put. Funny thing though; Male 1 has really seemed to come into his own. The soft sand and water are no problem for his oversized claws; and he's a whiz at getting clams open. His random mutation; once a disability, becomes an advantage. He grows sleek, strong and fat as he enters sexual maturity. He's now the dominant male; it's his genes the females want to pass on. So, he reproduces.
Over the years; his offspring and those of other woodhogs are no different than any others; save that those rare ones with long claws do better. Eventually, over time; long-clawed woodhogs become the rule; not the exception. Soon; short claws are gone completely as the gene is bred out. (This is what happens on the North shore. On the South shore; a similar change is happening; but these woodhogs like diving for fish; and develop powerful hindlegs. Eventually; they develop webbed feet.)
Back to the sea-beavers; compare the two animals now: Ultimately; woodhogs (now waterhogs) will grow a sculling tail; the feet will become flippers; and other adaptations will occur to turn them into fully aquatic sea beavers. But at no time will a waterhog bear a pup with a vertically fluked tail. Such an adaptation would be the most efficient; but there's no mutation that could create it...yet. Evolution chooses the simplest answers - making something already there a bit better; those with the new advantage thrive while those without are eventually replaced.) Back to the waterhogs. We've come perhaps a thousand generations since old male 1 started this mess; the species looks completely different. (and it is a different species now. Woodhogs still bumble around in the undergrowth; happily chomping termites.) North and South shore waterhogs have long interbred; mixing their two advantages. Waterhogs are larger, sleeker, more streamlined. They have valves over their nostrils and nictitating membranes on the eyes. Claws are still fashionable; but their paws are now large, flat and webbed fore and aft. The tail is much larger and broader as a body once built for ambling is losing out to animals built for swimming; with larger tails, heavier xyphoid processes to support bigger sculling muscles.
Some more thousands of years; and another evolutionary advancement: Flat tails provide a great advantage for diving and catching fish; so it's the flat-tailed adults that get to mate. The shape of the sea-beaver is now recognizeable.
To the present: Waterhogs still abound; surfing around the shorelines. Sea beavers take to the deeper water; diving to the ocean floor for abalone and clams; and no longer need to come to shore except to give birth. Eventually; evolution will create another creature resembling a dolphin; one that has no more need of dry land at all.

OK, ok; a long story. I could've just described the process; but I like having fun and letting my imagination go. :)
The point is everyone's right here - yes; evolution chooses the most efficient forms; but it does so in small steps; each simple answer leading to another simple answer. In no place does evolution skip steps and invent something totally new. That's what I mean by taking the simplest path.
Cheers!

HypersonicMan
2004-Mar-21, 03:33 PM
I think given the short amount of time Mars may have been habitable, life (if it ever existed) likely never got out of the unicellular stage. Remember, it took 3 billion years for life to go multicellular here on Earth.

Therefore, I believe that the most likely candidate for Martian fossils would be stromatolites (http://www.ucmp.berkeley.edu/bacteria/cyanofr.html)

HypersonicMan
2004-Mar-21, 06:06 PM
I think given the short amount of time Mars may have been habitable, life (if it ever existed) likely never got out of the unicellular stage. Remember, it took 3 billion years for life to go multicellular here on Earth.

Therefore, I believe that the most likely candidate for Martian fossils would be stromatolites (http://www.ucmp.berkeley.edu/bacteria/cyanofr.html)

Kaptain K
2004-Mar-22, 12:47 PM
Staiduk,

I agree with you up to this point:

...evolution chooses the most efficient forms...
Evolution does not choose "the most efficient form". Evolution choose the "adequate form". "Survival of the fittest" should be "survival of the good enough".

Staiduk
2004-Mar-22, 02:32 PM
Staiduk,

I agree with you up to this point:

...evolution chooses the most efficient forms...
Evolution does not choose "the most efficient form". Evolution choose the "adequate form". "Survival of the fittest" should be "survival of the good enough".

I agree; a much better word.

xbck1
2004-Mar-22, 05:33 PM
Fossils don't always need mineral-rich water to form, as was pointed out by Staiduk. In fact, many fossils didn't form in conditions like that. The fossils of the Gobi desert and many of the fossils found in places like Argentina are actually the original bones. I believe you can find an explanation of this in Jack Horner's book, Digging Dinosaurs, and you can also find a bit about it in the book Hunting Dinosaurs by Louis Psihoyos and John Knoebber.

I've also heard theories about the actual bone being replaced, but this is very unlikely to happen with water because it flows. In fact, fossils would be more likely to form in dry climates because the creature would form a mummy and then be covered with sand or something, like many of the fossils in Mongolia. Here (http://www.amnh.org/exhibitions/fightingdinos/ex-fd.html#) is a famous specimen that is apparently two dinosaurs that got trapped under some sand as they were fighting(?). Those are the original bones from millions and millions of years ago.