What Is A Fossil?

What Is A Fossil?

The fashionable use of the word ‘fossil’ refers back to the physical evidence of former life from a time period previous to recorded human history. This prehistoric evidence contains the fossilised remains of dwelling organisms, impressions and moulds of their physical type, and marks/traces created within the sediment by their activities. There isn't any universally agreed age at which the proof could be termed fossilised, nonetheless it’s broadly understood to encompass anything more than a couple of thousand years. Such a definition includes our prehistoric human ancestry and the ice age fauna (e.g. mammoths) as well as more historic fossil groups such as the dinosaurs, ammonites and trilobites.

The earliest reported fossil discoveries date from 3.5 billion years ago, nonetheless it wasn’t until approximately 600 million years ago that complex multi-mobile life started to enter the fossil report, and for the purposes of fossil hunting the majority of effort is directed towards fossils of this age and younger.

Fossils occur commonly around the world though just a small proportion of life makes it into the fossil record. Most living organisms simply decay without trace after loss of life as pure processes recycle their soft tissues and even hard parts such as bone and shell. Thus, the abundance of fossils within the geological report reflects the frequency of favourable situations the place preservation is possible, the immense number of organisms that have lived, and the huge size of time over which the rocks have accumulated.

How do fossils kind?
The time period ‘fossilisation’ refers to quite a lot of often complex processes that enable the preservation of organic stays within the geological record. It frequently contains the next situations: fast and permanent burial/entombment – protecting the specimen from environmental or organic disturbance; oxygen deprivation – limiting the extent of decay and likewise organic activity/scavenging; continued sediment accumulation as opposed to an eroding surface – making certain the organism remains buried within the long-time period; and the absence of excessive heating or compression which would possibly otherwise destroy it.

Fossil evidence is typically preserved within sediments deposited beneath water, partly because the circumstances outlined above occur more regularly in these environments, and likewise because nearly all of the Earth’s surface is covered by water (70%+). Even fossils derived from land, together with dinosaur bones and organisms preserved within amber (fossilised tree resin) were ultimately preserved in sediments deposited beneath water i.e. in wetlands, lakes, rivers, estuaries or swept out to sea.

Fossilisation may occur on land, albeit to a far lesser extent, and consists of (for instance) specimens that have undergone mummification within the sterile atmosphere of a cave or desert. Nonetheless in reality these examples are only a delay to decomposition rather than an enduring mode of fossilisation and specimens require everlasting storage in a local weather controlled atmosphere with a view to limit its affects.

In the following example a fish is used to illustrate the stages associated with fossilisation within off-shore marine sediments. This is just one summarised instance, in reality there are relyless eventualities that create the situations needed for fossilisation in marine sediments.

Having reached adulthood Crystal and mineral specimens returned to its beginning place to spawn, this specific fish reaches the end of its life and dies. Soon after demise the body of the fish becomes water-logged and sinks to the seafloor (note that quite often the gases produced during decomposition cause the carcass to drift back to the surface, so the ultimate resting place may be some distance away). More usually than not the carcass would be pulled aside and scattered by scavenging crustaceans and other fish, nevertheless on this event the absence of any massive scavengers leaves the fish comparatively undisturbed.


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