Fossils are the remains of ancient organisms, usually animals and plants but there are also minute bacteria and occasionally fungi. They are preserved by natural processes of burial. Most are entombed in sediment i.e. mud, silt or sand which with time transforms into a sedimentary rock such as sandstone. Rarely, fossils are enclosed in ash erupted from volcanoes, resin that oozes from trees and hardens into amber, or natural tar seeping from the ground. Normally only the resistant hard parts of organisms are fossilized. In the case of animals, these are mostly shells, bones and teeth, all of which contain biominerals secreted by the living animals. Only in rare instances of exceptional preservation are soft, fleshy tissues fossilized. Following burial, organic remains undergo various physical and chemical changes. They may be crushed or dissolved, their chemical composition can alter subtly or noticeably, and any holes in the structure may become filled with minerals precipitated from solutions that percolate through the rocks. If the fossil is deeply buried and subjected to high temperatures and pressures the fossils appereance will have changed from what it originally was.
Evolution is the process by which successive generations of organisms change. It is the reason we have many different species on the planet. To survive, an organism may have many offspring. Others must avoid being killed off. Some organisms live long enough to reproduce. The ones that reproduce and create successful offspring are likely for survival than those that don’t. The characteristics that helped the survival will be more common in the next generation than those of its less ‘fit’ relatives. This process is called natural selection. Natural selection is a critical aspect of the evolutionary process. The reason for diversity is mutation. Mutations are random alterations in our genes, Mutations can be minor, like a slightly longer neck, or they can be obvious, like...
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