When we think of keeping records, what comes to mind is a filing cabinet filled with a bunch of file folders with tax information or business records from years gone by. The fossil record is life's evolutionary filing cabinet, and it's full of genetic history that tells the tale of life and death on this planet in accordance with natural selection.
If you have ever been to the Grand Canyon or the badlands of Drumheller Alberta or even just the mountains or foothills, you will have seen some of the filing cabinet of the fossil record in the cliffs and hill sides. Some of what is seen there, may have been either an ancient lake or the very bottom of the ocean millions of years ago. When people climb or ski in the Rocky Mountains, they are actually standing on an almost 2 billion year old ocean floor that got pushed high up into the air as the Continental Divide plates shifted and squeezed together. When the tectonic processes of subduction, causes a continent to ride forcefully over an oceanic plate, or the convergence of two or more continents, a new formation of a mountain ranges occurs.
These events have pushed up huge mountain ranges, on the land, and in the seas, and many of these mountains, like the Mountains in the Appalachians, over long periods of time, have been almost completely worn away. In plate tectonics, one plate gets pushed upward from the ocean bottom, becoming the mountain tops and the other plates get pushed under, and back down into the earth's molten core. The event that formed the Rockies, took place somewhere around 85 million years ago, back in a time when life was just beginning to blossom on the planet, and there wasn't a vertebrate to be found anywhere.
Some of the earliest fossils ever found, have been found on mountain tops. It was a time before the mammals, and long before the dinosaurs thundered across the earth. The Rocky Mountains, or the Rockies, as we call them here in Canada, are the major mountain range in western North America. The Rocky Mountains stretch more than 3,000 miles from the northern British Columbia, in western Canada, to New Mexico.
In a sense the fossil record is all around us, but until it gets "dug up" and filed, it officially won't count. This record of life is the accumulation of artifacts by the diligent hands of those amateurs and professionals in the field who put the "files in the folders" and record what they have found. Without human hands and minds, there would be just a jumble of old bones and shells, ancient rocks lying in a heap or packed away in crates in a museum's basement. It's only due to the people who sort and catalogue each piece that we finally get an image of how life evolved over the millennia!
The word "fossil" comes from the Latin word "fossus", which literally means, "having been dug up". The remains of animals and plants are also known as "zeolites". The study of fossils that have formed periodically over "geological time", which is the time, as looked at through the records of the planetary evolution itself, makes the study of Paleontology possible. The earth's crust shifts and slides constantly on a mantle of molten rock. The thin part of solid earth that we walk on and that oceans and all the life in them exist, has been changing for millions of years.
If it were possible to flip the pages of the fossil record like a motion picture, people would see the movement and surge of life across four billion years of geological time passing. As scientists record and piece more and more of the record together the "big picture" becomes that much clearer! But first human hands have to put every piece of stone, every imprint of every bit of life from the past, into some sort of order, from the chronological "heap" where the bones are now.
The fossils of the oldest forms of life are not actually in their original form. But instead they are merely a stone photocopy of what they were originally. If you can imagine, after the animal dies, in order for it to become a fossil, it must first fall in an area where water and or volcanic ash or sand can cover it. This is why not every animal or plant gets fossilized. Once the animal is covered completely the process of decay begins, but because it happens without the presence of air, it takes a very long time. As each minute bit of organic matter is lost it gets filled in with some of the sand or ash above it. Over time the organic matter is pretty much completely replaced with sand or ash and when it hardens, a fossil is formed!
The youngest fossils start appearing around the beginning of the Holocene Epoch, and the oldest ones on record are estimated during the Archaen Eon, approximately 3.4 billion years ago. Throughout human history people have tried to explain what fossils were and how they came to be where they were found. Most of the explanations were embedded in myth and folklore, and so have very little importance in modern times.
In China fossils bones were thought to have belonged to dragons, and were often ceremonially worshiped and put into medicines. The ancient Greeks were the first of people in history to realize that perhaps these belonged to creatures that lived in the sea. Later in human history, Leonardo Da Vinci would also proclaim that the fossils found had in the distant past been the remains of living creatures. Early Naturalists, the people who studied the nature of things around them, began to contemplate and develop a way to define and catalogue these discovered fossils. It wasn't until Darwin and his peers that links were drawn, and the tree of life began to become more visible. Charles Darwin described the "process of descent" with modifications caused by evolution. He described evolution as the adaptation of all living things to the natural pressures put upon them by their environment.
Since Darwin's time, discoveries have been made which pushes back the fossil record to between 2.3 billion and 3.5 billion years. Almost since the formation of the earth and its geological record! Today archaeologists have discovered that the fossil record shows how some species have remained essentially unchanged for millions of years. A species will only undergo major change, if its environment changes in a way which leaves it significantly less well adapted to survive. Without the fossil record people would all still be asking the age old questions regarding how humans got here.
Most of the fossils found during the Precambrian Period were microscopic bacteria or microfossils. However, macroscopic fossils are now known to have mostly originated during the late Proterozoic. This gives us a glimpse into the time when no mammals or fish lived on the planet. A record that shows that after the evolution of microscopic life, there was a surge of plant life that flourished in its ocean and perhaps even land environments for millennia before anything walked or swam on earth.
Perhaps not all things are disclosed by the fossil records science currently has, but then again, perhaps someday soon there will be revelations which will complete humanity's understanding of how life began in the first place. Perhaps it will help people to avoid the annihilations and extinctions of those long dead creatures that no human would truly understand, without the backdrop story revealed by the current fossil record. Today the fossil record is life's evolutionary epic that unfolded over four billion years on this planet and it will continue to unfold long after humans are gone.