| The age of the fossils |
 Sedimentary processes can occur anywhere on the earth's surface where there is erosion, but not all the deposited material becomes rock sedimentaris. as erosion can drag itself sediment before it hardens. Basically, sedimentary processes are of three types: Marine deposits form on the continental shelf and abyssal zones. Continental materials accumulate at the foot of the mountain ranges in the glaciers along the basins of the rivers and deserts. Transition, which is the sedimentation that takes place at points of contact between the ocean and continents, such as wetlands and deltas. The organic remains trapped in sediment can be fossilized if they become metamorphic rocks. The set of the various layers that contain the same types of fossils is called a stratigraphic unit. The thickness of a sediment can be deduced from the time it took to form, if known sedimentation rate. Each type of sediment indicates some features of her time when it formed, such as rain, ice ages, desertification, ... This allows geologists know the age of the sediment and therefore also the age of fossils from continuing, resulting in a good way of dating.
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