"No fossil is buried with its birth certificate" - Henry Gee, in Search of Deep Time: Beyond the Fossil Record to a New History of Life.
Fossils, the preserved remains, traces or impressions of life, are the physical evidences of past life and the environment. They freeze the time, many a times capturing the conditions a million years away from where any human began! These humble things speak volumes. A tiny shell can recite about the environment conditions and composition. Huge information is derived from them- past geologic time, mode of life, palaeoecology, how our Earth was, how life has evolved, and why we can relate or correlate one place to other. They even help us to 'categorise' or break the vast span of 4.6 billion years since Earth formed thus providing the 'Relative time'. The geological events are best described on basis of fossil content and a 'staircase' of time can be constructed.
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| http://www.stratigraphy.org/index.php/ics-chart-timescale |
The Hadean Eon is the 'hidden'portion of geologic time with negligible rock record or diagnostic fossils. The Archaen Eon often called as Eon of first life shows oldest know fossils. The first life forms probably arose around 3.8 billion years ago in the form of primitive organisms resembling bacteria and cyanobacteria. The Proterozoic saw multicellular life, colonial algae, sponges, and soft bodies invertebrates. The Ediacaran fauna dominated from 635 to 541 Ma. The Phanerozoic came with complex life. The Palaeozoic Era saw a dramatic explosion of life, during Cambrian (Cambrian explosion), where most widespread diversification of life occurred, especially in oceans. Trilobites dominate the Cambrian fossil record. Life's quest on land too began by end of Ordovician. Plants began to colonize land. Jawless fishes, molluscs and corals flourished in oceans. First land plants, first amphibians, appearance of first reptiles characterizes Palaeozoic. Huge forest swamps occured in Carboniferous and Permian (that is how we get most of the coal from this strata). What started with a great explosion of life ended with a dramatic extinction in Palaeozoic. The Permian extinction, the greatest extinction event in history of Earth, devastated marine biota-corals, echinoderms, graptolites, crinoids, trilobites. The lineages that survived went ahead in evolution and spread.
Reptiles flourished and dominated the next era to come- Mesozoic. Dinosaurs ruled (remember Jurassic Park?) . Invertebrate life was dominated by the Ammonites and Belemnites along with Sponges, Crinoids, Echinoids. Crustaceans such as the first crabs made their appearance. Brachiopods declined, while Bivalves become more abundant. Amphibians were represented too. Flowering plants, or angiosperms also first appeared during this span. The famous Archaeopteryx, appeared in the upper Jurassic. The end of Cretaceous saw another huge event in geologic history with extinction. Dinosaurs were wiped out along with some marine invertebrates. The Cenozoic Era began with extinction of dinosaurs and is called "Age of Mammals". Whales, Saber tooth cats, horses, apes, elephants, giant sloths and finally humans appeared ~ 2-1.8 Ma.
So, the way life has evolved and formed this complex staircase is extremely important in Palaeontology. The study of these fossils and their various aspects of formation, characteristics, types, evolution, etc. converges into a branch called Palaeontology. Fossils include everything from skeletons, teeth, impressions, parts preserved, cast or mold, tracks, bores, etc. From micro fossils to massive mammoths. A very small amount of life is preserved as fossils, as most of it decays. This process of preserving or fossilization in itself is complex yet wonderful. Rapid burial of the life form, undisturbed conditions, quick accumulation of sediments are some basic necessities. Best preserved in sedimentary rocks, on rare occasions unaltered remains or entire form may be preserved (extreme cold, dryness). Most of the times, it may be altered, or a cast or mould is formed. We have mega fossils, which may be from animals or plants. Then there is Micropalaeontology, which deals with study of remains of micro organisms preserved as micro fossils. It is a
huge weapon with numerous applications and scope. Summed beautifully as " The microscopic organisms are very inferior in individual energy to lions and elephants, but in their united influence they are far more important than all of these animals. " (Kennett, 1988). Ichnofossils, includes tracks & trails, bores-borings, footprints, coprolites, etc.
Fossils-the connecting links, the guiding tools, and literally a data chip holding information several 'GB' in a single place, maybe primitive but modern day geology and discoveries are still based on them.
Some things last forever, no not just diamonds :)
And Nature ensures it has created good impressions- the footprints in sands of time, the geologist's clock!
P.S: My love for fossils is pretty 'recent', ever since I own one gifted by a dear friend <3 Thanks!
