FOSSILS, FOSSIL TYPES and FOSSILIZATION

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FOSSILS are evidences of organisms that lived in the past. They can be actual remains like bones, teeth, shells, leaves, seeds, spores or traces of past activities such as animal burrows, nests and dinosaur footprints or even the ripples created on a prehistoric shore.

Molds - Impression made in a substrate = negative image of an organism e.g. Shells
Casts - When a mold is filled in e.g. Bones and teeth
Petrified - Organic material is converted into stone e.g Petrified trees; Coal balls (fossilized plants and their tissues, in round ball shape)
Original Remains - Preserved wholly (frozen in ice, trapped in tar pits, dried/dessicated inside caves in arid regions or encased in amber/fossilized resin) Woolly mammoth; Amber from the Baltic Sea region
Carbon - Film Carbon impression in sedimentary rocks e.g. Leaf impression on the rock
Trace / Ichnofossils - Record the movements and behaviors of the organism e.g. Trackways, toothmarks, gizzard rocks, coprolites (fossilized dungs), burrows and nests

THE SIX WAYS OF FOSSILIZATION
1. Unaltered preservation - Small organism or part trapped in amber, hardened plant sap
2. Permineralization/ Petrification - The organic contents of bone and wood are replaced with silica, calcite or pyrite, forming a rock-like fossil
3. Replacement - hard parts are dissolved and replaced by other minerals, like calcite, silica, pyrite, or iron
4. Carbonization or Coalification - The other elements are removed and only the carbon remained
5. Recrystalization - Hard parts are converted to more stable minerals or small crystals turn into larger crystals
6. Authigenic preservation - Molds and casts are formed after most of the organism have been destroyed or dissolved

More than 90 percent of all organisms that have ever lived on Earth are extinct. This is due to mass extinctions events that wiped out organisms in the past.

Geologic Time Scale - History of Life on Earth
Dating Fossils : Relative Dating and Absolute Dating