WHAT ARE FOSSILS AND WHAT IS PALEONTOLOGY?
The only direct way we have of learning about dinosaurs is by studying fossils. Fossils are the remains of ancient animals and plants, the traces or impressions of living things from past geologic ages, or the traces of their activities. Fossils have been found on every continent on Earth, maybe even near where you live.
The word fossil comes from the Latin word fossilis, which means “dug up.” Most fossils are excavated from sedimentary rock layers . Sedimentary rock is rock that has formed from sediment, like sand, mud, small pieces of rocks. Over long periods of time, these small pieces of debris are compressed (squeezed) as they are buried under more and more layers of sediment that piles up on top of it. Eventually, they are compressed into sedimentary rock. The layers that are farther down in the Earth are older than the top layers.
The fossil of a bone doesn’t have any bone in it! A fossilized object has the same shape as the original object, but is chemically more like a rock.
Paleontology is the branch of biology that studies the forms of life that existed in former geologic periods, chiefly by studying fossils.
What Do Fossils Look Like?
Fossils have the same shape that the original item had, but their color, density, and texture vary widely. A fossil’s color depends on what minerals formed it. Fossils are usually heavier than the original item since they are formed entirely of minerals (they’re essentially stone that has replaced the original structure). Most fossils are made of ordinary rock material, but some are more exotic, including one fossilized dinosaur bone, a Kakuru tibia, which is an opal!
HOW FOSSILS FORM
Fossils of hard mineral parts (like bones and teeth) were formed as follows:
- Some animals were quickly buried after their death (by sinking in mud, being buried in a sand storm, etc.).
- Over time, more and more sediment covered the remains.
- The parts of the animals that didn’t rot (usually the harder parts likes bones and teeth) were encased in the newly-formed sediment.
- In the right circumstances (no scavengers, quick burial, not much weathering), parts of the animal turned into fossils over time.
- After a long time, the chemicals in the buried animals’ bodies underwent a series of changes. As the bone slowly decayed, water infused with minerals seeped into the bone and replaced the chemicals in the bone with rock-like minerals. The process of fossilization involves the dissolving and replacement of the original minerals in the object with other minerals (and/or permineralization, the filling up of spaces in fossils with minerals, and/or recrystallization in which a mineral crystal changes its form).
- This process results in a heavy, rock-like copy of the original object – a fossil. The fossil has the same shape as the original object, but is chemically more like a rock! Some of the original hydroxy-apatite (a major bone consitiuent) remains, although it is saturated with silica (rock).
Here’s a flow chart of fossil formation:
There are six ways that organisms can turn into fossils, including:
- Unaltered preservation (like insects or plant parts trapped in amber, a hardened form of tree sap)
- Permineralization=petrification (in which rock-like minerals seep in slowly and replace the original organic tissues with silica, calcite or pyrite, forming a rock-like fossil – can preserve hard and soft parts – most bone and wood fossils are permineralized)
- Replacement (An organism’s hard parts dissolve and are replaced by other minerals, like calcite, silica, pyrite, or iron)
- Carbonization=coalification (in which only the carbon remains in the specimen – other elements, like hydrogen, oxygen, and nitrogen are removed)
- Recrystalization (hard parts either revert to more stable minerals or small crystals turn into larger crystals)
- Authigenic preservation (molds and casts of organisms that have been destroyed or dissolved).
Most animals did not fossilize; they simply decayed and were lost from the fossil record. Paleontologists estimate that only a small percentage of the dinosaur genera that ever lived have been or will be found as fossils.
Most of the dinosaur skeletons that are shown in museums are not actually fossils! They are lightweight fiberglass or resin replicas of the original fossils.
Why are Fossils Rock-Colored?
Because they ARE rocks! A fossilized object is just a rocky model of an ancient object. A fossil is composed of different materials than the original object was. During the fossilization process, the original atoms are replaced by new minerals, so a fossils doesn’t have the same color (or chemical composition) as the original object. Fossils come in many colors and are made of many different types of minerals, depending on what the surrounding rock matrix was composed of; one dinosaur bone (Minmi) is an opal.
Also, some fossils of skin (and other soft body parts) have been found. Again, the color of the skin is not retained during the fossilization process, all that remains today is a rocky model of the original.
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What Is the Difference Between Artifacts & Fossils?
A fossil, not an artifact
trilobite image by Alison Bowden from Fotolia.com
Fossils and artifacts can both be found buried in the earth. The difference between them is that fossils are the remains of living creatures; artifacts are man-made objects.
Fossils
- Fossils include the remains of dead animals and plants or the imprint left by their bodies in the rocks. In fossilized remains, the original living tissue has been replaced by minerals leaching in over the millennia.
Artifacts
- Artifacts are made by humans. Typical artifacts found by archeologists include coins, weapons, gems, sculptures and vases.
Legal Differences
- Because many artifacts found in America were made by the ancestors of present-day Native Americans, there are more restrictions on collecting or selling them than on fossils. Some fossils may be collected on federal land, for instance, but not artifacts.
Differences in Age
- Archeological artifacts can be found dating back many thousand years. The earliest fossils date back almost four billion years.
Differences in Analysis
- Artifacts are analyzed by comparing them to the style and make of similar objects or situating them in the known history of the area in which they were found. Because fossils are so much older, there are other tools for studying them, such as the kind of rock formation in which they were found.
Writing by Fraser Sherman
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