How Are Fossils Formed

Tuesday, August 10, 2010

When I was a child, I thought I would make my own fossil. So I took the body of a bird that had died in the yard and buried it in the garden thinking it would become a wonderful fossil like that ones I saw at the natural history museum. You know how well my experiment worked out. When I went back a few weeks later, I found that the bird's body had been reclaimed by nature and had begun to become part of the garden itself. I left it there.

The very fact that we have dinosaurs fossils at all shows that from time to time the natural order of things doesn’t happen the same exact way. Our planet and the way nature works is built on the theory of recycling. So when something dies in nature, something either eats it or it decays and becomes part of the soil again to feed plants which grow fruit to feed birds who feed animals and the cycle is repeated. When a creature becomes fossilized, something different happens. And how that happens is a pretty fascinating twist on how nature works.

The first element in fossilization is water. While some fossils are formed in mud or ice, the presence of moisture is part of the formula. Most fossils were formed when an ancient animal, perhaps a dinosaur, dies and is submerged in water either because it fell into a lake or ocean or some form of water migration buried the corpse in water before it had naturally decayed. Because the body is cut off from air, the normal process of decomposition does not occur exactly the same way as above ground.

The body will settle into the floor of the lake or ocean where it settles to be processed by bacteria and sea creatures who will dine on the soft flesh and body parts of the animal. But these underwater recyclers will leave the skeleton intact, which becomes the base material for our future fossil find. The bones will settle further into the mud at the bottom of the seabed. Very often that settling will leave the structure of the animal relatively intact which is delight when we find a fossil in that good of shape.

Over time sentiment buries the bones and many thousands of years slowly changes the nature of the bone matter essentially turning the skeleton into rock to become part of the solid matter around it. By this time, that fossil may be buried very deep under the floor of the ocean. But the earth is always moving and changing and millions of years of that movement may cause the rock to emerge from the water and become dry land.


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