Fossils are the preserved remains of animals, plants, and other organisms. The word fossil can also refer to traces that have been preserved, such as footprints. The “fossil record” refers to all the fossils, and considers where they were found in the earth to create a timeline of life on Earth. Those who study fossils are called paleontologists.
Fossilization is actually quite rare. Most creatures decompose quickly after death. In order to become a fossil, the remains must be covered by a fine layer of sediment to stave off predators and decay. Lacking the sediment, an organism can become a fossil by being frozen, desiccated, or deposited into an oxygen free environment, like a bog.
Fossils usually refer to the bones and other parts of the organism. However, traces of these creatures can also turn into fossils. Dinosaur feces, called coprolites, become fossilized and are now studied for clues to the diet of dinosaurs. Fossilized footprints and skin imprints have also been found. This type of fossil is known as a trace fossil (“ichnofossil”), to distinguish them from the fossils of bodies.
The oldest fossils on earth are made of stromatolites, similar to modern blue-green bacteria. These single celled organisms were able to make large mats containing many microorganisms. Most scientists now accept that the large colonies of cyanobacteria created not only the banded iron formations, but also the oxygen we breathe today.
Throughout history, people have been finding fossils. In China, these fossils were seen as Dragon bones, and were used as aphrodisiacs and in medicine. In the West, fossils found on mountainsides were proof of the great flood of biblical times. It wasn’t until the Renaissance that science began to seek an explanation outside of religion.
By the time Charles Darwin wrote his groundbreaking book, On the Origin of Species, fossils have been found that were 540 million years old. Since then, our knowledge of the fossil record has increased exponentially. Fossils have been discovered which date back between 2.3 to 3.5 billion years ago.
Today the fossil record is seen as the story of life as it unfolded over 4 billion years. Paleontologists have joined forces with biologists to find out the secrets of fossils.they have their work cut out for them – fossils are very difficult to find. Macro fossils like dinosaurs and other large animals are commonly displayed in museums around the world. Still, micro-fossils, tiny fossilized remains of microscopic organisms, are more common and provide a great deal of information.
While most fossils are found in the ground, some are found in resin. Amber, fossilized tree sap, often includes insects, spiders, and occasionally even vertebrates like small lizards. Creatures preserved in resin fossils are preserved exquisitely. Small fragments of DNA had been teased out of certain resin fossils.
Today, the term “living fossil” refers to a living species which closely resembles another species known only from fossils. The coelacanth was believed to be extinct until a living specimen was found in the early 20th century. The Kagu bird of New Caledonia is the last of its kind, with all close relatives existing as fossils. Other living fossils include the horseshoe crab, the Nautilus, and the tuatara lizard.