Fossilization

There is some debate over the meaning of the word "fossil." If you had a text book that tried to define it growing up, you probably had the most commonly accepted definition that a fossil is "the remains of a living thing."

That's awesome. Road kill is fossil, scat is fossil, people in graveyards are fossils even the ones that died in the past century....

I really don't like that definition.

The next most commonly accepted definition is that there is an arbitrary time break; if an object is older than such, it is a fossil. If younger, it is not.

Ok... so where do we draw the line? Somewhere in the hundreds? Some living trees have seen that much time. Thousands? Well, mammoths are actually relatively recent animals and you may leave them out. Millions? Well, then you really just left out the mammoths, and people too.

I was taught that a fossil has to be altered or seen replacement in some way. For example, a track will  be filled in; it isn't in its original rock. Chemistry happened, and at least a little bit of the bone is replaced. If something hasn't changed, maybe its still organic matter. Its still really cool, but it hasn't under gone fossilization.

People don't like that. See, we don't actually know that much about the fossilization process, not enough to be able to define an old word off of it.

However, fossilization does imply some sort of change occurring. If a bone or other remains are completely the same as the originally were, such as a frozen mammoth, I'd say they've been preserved. Mummies tend to fall into this category.

So let's talk about the fossilization of the area.

Fossils, in general, when exposed to air have the potential to become very brittle. They've been removed from the environment that they have been in for millions of years, and frankly they don't like that. In North Carolina, where the air is moist, it's really bad for any fossil that has iron because of something called pyrite disease, which causes crystals to grow on and weaken fossils. NC fossil hunters, I recommend getting a lot of those little salt packs that come in shoe boxes. They help keep the air in your cases nice and dry.

Other times, like in some of the fossils nearby where I am in Nebraska, the iron in the fossils can cause them to turn red. This is similar to rust; basically a redox (reduction/oxidation) reaction occurs. Don't know chemistry? Every element has a slight charge to it, like a battery. Some elements can handle being 'charged' better than others, bringing them closer to neutral. So depending on the elements in the fossil and the surrounding sediments and liquids, different chemistry will happen, in this case turning the fossils a reddish color.

 Other fossils, like those exposed in the ash bed (and this guy) were exposed to and absorbed silicates and calcium carbonates. Not nearly as stable. In fact, a little weathering and they're gone. They're very brittle, and we have to be really careful with these guys. They will collapse under their own weight if not given good support, and we really take care to protect them from the weather. The building is even heated in the winter to prevent 'freeze-thaw,' which causes them to expand and contract, leading to them eventually shattering.

More stable, however, are these guys. They were exposed to manganese, much more stable. This came from source rock in the Rocky Mountains that had been deposited somewhere closer to Nebraska and then brought in as till by the glacial advances. See how they are just kind of sitting on the floor unlike the other two? They are fine.

So, I enjoy this stuff. I really want to get a better grasp on the chemistry behind it so that I can actually look into this. Rick and I had a really interesting conversation today about how these processes could be modeled, seeing as we really don't understand fossilization that much right now. We know that rapid burial is a key; everywhere else in Nebraska, only one or two feet of ash were deposited over the same period of time as the 10 feet we see in the ash bed here at Ashfall. Because the wind was blowing it into but not out of the water, anything in the water was being buried faster than anything anywhere else in Nebraska, easily covering rhinos and horses with 6 more feet of ash above them. Two feet would barely hide a rhino.

Fun fact: fossilization probably doesn't actually take millions of years. It probably happens pretty early on after an animal dies, or else the bones would basically turn into dust from exposure and scavengers. How it happens, however, is not well documented.

Who cares how fossils preserved, many will ask? We just want to see the bones in a museum on display.

Well, as we come to understand more about the "how" and "why," we can narrow down where to look more than we have, and paleontology would be less of a shot in the dark. And maybe put a few more on display for you!

I love these questions. Fossilization was something I tackled for some elementary school project on a really basic, immature level. I basically modeled total replacement, petrification, what happens to trees (...but I did it with bones.) Maybe someday, I can tackle the other factors and types with not just ideas, but experiments. Why did the unhealthy bone in the ashbed preserve white while the healthy bone is black? Are they different chemically, and in stability? What needs to be done 10 years from now to keep everything intact?

Finding questions. This is how a new generation of paleontologists is born.