What is a Fossil?
Fossils are the remains or traces of ancient life that have been preserved by natural processes, from spectacular skeletons to tiny sea shells. Imprints, tracks and trails can also become fossilised, like dinosaur footprints or worm burrows. These are called trace fossils. By studying the remains of life and the traces it left behind we can learn a lot about how animals and plants lived and behaved millions of years ago.
Types of Fossils:
1. Body fossils – Soft parts:
The first type, body fossils, are the fossilised remains of an animal or plant, like bones, shells and leaves. These can be mould and cast fossils, like most of the fossilised dinosaur skeletons and big bones we see, replacement fossils, like petrified wood, or whole body fossils – mammoths caught in ice, or insects trapped in amber. A mold is the imprint left by the shell on the rock that surrounded it. An external mold is a mold of the outside of the shell. Each time we break a shell or bone out of the rock, an external mold is left behind. Molds of the underside of shell may be left on the surface of rock that formed when sand or mud filled the inside of the shell. These are called internal molds.
2. Molecular fossils:
Molecular fossils are often referred to as biomarkers or biosignatures and represent products of cellular biosynthesis that are incorporated into sediments and eventually into rock. Many of these chemicals become altered in known ways and can be stable for billions of years.
3. Trace fossils:
Trace fossils are marks left by an animal or plant that has made an impression. These
include nests, burrows, footprints or any other markings of the animal’s time on the earth. The structure of the animal or plant remains as a mineral form. The colors of the minerals that replace the form can be dazzling. Sometimes they are made into art and jewelry.
4. Carbon Fossils:
All living things contain an element carbon. When an organism dies and is buried in sediment, the materials that make the organism break down and eventually only the carbon remains. The thin layer of carbon left behind can show an organism’s delicate parts like leaves or plant e.g. fern fossil 300 million years old.
Sometimes watery solutions of various minerals speed through the sediments and it takes the shape of some plant part or animal. Their study shows that they are neither plants nor animals. Such fossils are called pseudofossils.
Taphonomy is a field of paleontology, paleoanthropology, and archaeology that studies human and animal remains in relation to the post-mortem (after death) transformations that occur in burial sites. From the Greek, taphos, meaning tomb or grave, and nomy, meaning classification. In a broader sense, taphonomy is the study of the processes that leads to fossilization, as well as the stages of transformation of remains through the action of environmental factors. The knowledge gathered by this field is important to forensic science as a tool for the analysis of human remains at old crime scenes, mass graves, and mass disaster areas.
How are Fossils Made?
Living things (usually aquatic) die and then get buried quickly under sand, dirt, clay, or ash sediments. Usually, the soft parts decay, or rot away, leaving the hard parts behind. These are ammonites, one of the most common fossils that are found. As time goes on more and more sediment accumulates.
Pressure, heat, and chemical reaction cause the sediments to harden into a rock called sedimentary rock. Movements in the earth’s crust pushes the layers of sedimentary rock back up to higher ground. Finally, through erosion caused by weather, wind, and water, the fossils become exposed at the surface again.
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