Fossils are essential to our knowledge of the earth’s history before humans, and their contribution to our understanding of the planet and the evolution of its wildlife is invaluable. Without the existence of a fossil record, we would know little to nothing about prehistoric life on our planet and how it evolved over time, whether it be animals, plant life, or even the most basic of life’s building blocks, micro organisms. The formation of fossils is a rare event however, and an understanding of how they are formed is essential to the preservation and study of fossils. While the first fossils to be discovered were largely misunderstood by those who found them, research began to paint an accurate picture of their origins and the process of their formation in fossiliferous materials became incredibly important to our understanding of what time period they belong to.
It is important to understand that fossils contain only trace amounts of the organism that it represents, such as remnants of bones and teeth. The majority of the fossil is actually crystallized mineral deposits that take the shape of the creature. While there are several ways that fossils are formed, the most likely area to find them is where large bodies of water once existed. It was here that premineralization of the organism occurred most often, which is the predominant method by which fossils are created. In the premineralization method of fossil formation, groundwater occupies the empty spaces within an organism immediately after death. The water carries minerals with it that are left behind after sufficient evaporation has taken place. These minerals can fill even the smallest of spaces, including the walls between cells themselves, and they can create an extremely accurate representation of the organism after the body has deteriorated.
Some of the Earth’s oldest fossils are called stromatolites, and they are billions of years old. These fossils were formed by multiple layers of sediment that were deposited over time and retained the shape of the organism after its remains vanished. In this case there are no minerals present and the surrounding materials simply formed around the creature, leaving an impression within its layers of what the creature looked like. In this situation the fossil is more of an imprint or indentation of the creature, rather than a representation that has been created from the inside. This type of fossil is most prevalent in the discovery and study of micro organisms and bacteria, whose size makes them difficult to view with the naked eye.
Compression fossils are formed by yet another fossilization method, one which is chemically based. Fossils formed by geochemical alteration are usually a different size and color than the actual creature. This difference is because of a chemical reduction of the organism’s complex organic molecules. In the compression method the materials that make up an organism are subject to carbonization and in its wake only a geochemically-altered fossil remains. Yet another type of fossil, resin fossils, are formed when an organism is trapped within amber colloquially, or sap. The oldest of these specimens date back to the Triassic period, and have been the genesis for many modern science fiction tales.
Not all fossils are remnants of living creatures though, some are considered to be only trace fossils that point at the existence of an animal. These trace fossils may include feces from an animal or even a footprint. These are formed in the same manner as other fossils, usually leaving behind a mold, or cast, of the footprint or specimen. From these artifacts we can learn much about the earth’s past, including the dinosaurs that once roamed the land, and the ferns and conifers that once dominated the landscape. Most importantly we can learn how these creatures lived and coped with the world around them, and perhaps someday we may discover what caused their extinction.