ACCORDING to the process by which they are formed, or to the evidence, they have left behind.The method by which fossils are formed is termed fossilization. Fossilization is also known by the name ''Preservation'' Some types of fossils include petrification, compression, impression, etc.Impression: An Impression fossil is the commonest form found in VARIOUS types of sedimentary rocks, such as shales, sandstones, limestones, etc. These fossils represent only an imprint of the plant part. The original ORGANIC matter has been completely destroyed.Compression: Compression Is only a degree of an impression when the organic remain of the plant part actually remain in the fossil but is highly compressed. The great pressure under which fossilization takes place flattens out all-round or solid organs so that what remains in the fossil is usually a carbonaceous film.Petrification: It is the best but perhaps the rarest type of fossilization. This literally means a transformation of the organic tissues into stone.The buried plant material absorbs mineral solutions like silicates, carbonates, phosphates, etc., and infiltration followed by precipitation takes place so that silica, calcium, carbonate gets impregnated within the tissues. Eg – Coal Balls AcclimatizationIt is the process in which an individual organism adjusts to a change in its environment, allowing it to MAINTAIN performance across a range of environmental conditions.PasteurizationPasteurization refers to the process of heating the milk and again cooling it down so that the microorganisms present are killed.This process is followed in order to increase the shelf-life of milk and also the quality of milk products. TyndallizationIt is the process of sterilizing edible substances so that heat-resistant ENDOSPORES can be killed.It is named after its inventor, scientist John Tyndall