Fossil Facts
What are fossils and what is paleontology?
- Paleontology is the branch of biology that studies the forms of life that existed in former geologic periods, primarily by studying fossils.
- 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.
- 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, and small pieces of rock).
Over long periods of time, these small pieces of debris are compressed (squeezed) and are buried under more and more layers of sediment that piles up on top of it. Eventually, they are compressed into sedimentary rock.
- 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.
Other ways fossils form: Petrification
Petrification can preserve hard and soft parts and slowly replaces organic material with silica, calcite or pyrite, forming a rock-like fossil. Wood is often found petrified.
- Some organisms are embedded in Amber (a hardened form of tree sap). This usually preserved insects or pieces of plants.
- Fossils of imprints may form, like casts of dinosaur footprints. The impressions, in the right circumstances, fill with sediments that fossilize.
- Most animals did not fossilize; they simply decayed and were lost from the fossil record. Paleontologist’s estimate that only a small percentage of the dinosaurs that ever lived have been or will be found as fossils.
How do Fossils Form?
Not many plants and animals are lucky enough be turned into fossils.
When an animal or plant dies its remains usually rot away to nothing. Sometimes though, when the conditions are just right and its remains can be buried quickly, it may be fossilized. There are several different ways fossils are formed. Here we go through the five steps of fossilization to make a typical ‘mould and cast’ fossil.
An animal dies; its skeleton settles on the sea floor and is buried by sediment.
An animal dies and its body sinks to the sea floor. The soft parts of the animal rot away, leaving only its skeleton. The skeleton is buried by sediment (like mud or sand) falling from the ocean above. The sea floor is an ideal place for fossilization, which explains why many fossils are marine (from animals that lived in the sea). Land animals may die and be swept out to sea to be buried in the same way.
The sediment surrounding the skeleton thickens and begins to turn to stone.
The skeleton continues to be buried as sediment is added to the surface of the sea floor. As the sea floor sinks, pressure increases in the lower layers of sediment and it turns it into hard rock.
The skeleton dissolves and a mould is formed.
Now buried at depth and surrounded by stone, the skeleton is dissolved by ground water. This leaves a cavity (or hole) preserving the shape of the original skeleton. This cavity is known as a natural mould.
Minerals crystallize inside the mould and a cast is formed.
Water rich in minerals enters the mould, and fills the cavity. The minerals deposited in the mould form a cast of the mould. This cast has the same shape as the original skeleton, but none of its internal features.
The fossil is exposed on the Earth’s surface.
Millions of years later, the rock surrounding the skeleton rises to the Earth’s surface (this happens during mountain building, earthquakes and other earth processes). The rock is worn away by wind and rain, and the fossil is now exposed, waiting to be found!
Types of Fossils
Rocks and Minerals
