Date Posted: 5/25/2013 10:11:56 AM
Posted By: Awilow Membership Level: Bronze Total Points: 45
The theory of evolution suggests that in the course of the earth’s history, new life forms arose from pre-existing ones. The new forms, if suited to their new environment, reproduced and gave rise to similar offspring. Variations arising in subsequent reproductions eventually gave rise to offspring that differed markedly from their parental forms. These variations when perpetuated in subsequent generations led to formation of new species.One of the Evidence supporting organic evolution is fossil recordsFossils are remains of ancestral forms that were accidentally preserved in some naturally occurring material for example sedimentary rocks and plants resins. The study of fossils is called palaeontology. The most common method of fossil formation is petrification that is, changing into rock - This is usually possible for hard body parts like bones, teeth, shells and woody parts of plants. Fossils are also formed by preservation of the entire organism or its parts, commonly found in amber, plant resins and ice. Other fossils can be found as impressions such as casts and moulds, sedimentary rocks such as limestone and sandstone.Fossils are important because they give direct evidence of the type of animals and plants that existed at a certain geological age. These records show that the different groups of organisms arose at different times on earth. For example, earliest fossils are of Monera, followed by protoctista and then fungi. Plants and animals appeared later. Even among the vertebrates the oldest fossils are those of the fishes, followed by amphibians and progressively mammals are the latest organisms to appear on earth.By comparing fossils of different organisms, it is possible to tell the phylogenetic relationships between organisms. Fossil records also show gradual increase in complexity of organisms over time. Older (lower) rock strata contain fossils showing simple structures while younger (upper) rock strata contain fossils showing more complex structures.Some fossil records have been used to reconstruct an almost complete evolutionary history of development of certain organisms. For instance, human fossils show progressive increase in skull sizes to the present age while evolutionary stages of the horse have been reconstructed on the basis of increased complexity of fossil limbs. The age of recent fossils can be determined through radioactive dating using carbon– 14 while that of very old fossils is determined by determining the age of the rocks where the fossils are found using potassium – argon method.However, use of fossil records in retracing evolutionary history of all present–day organisms have some limitations in that:(i) There are several missing fossil records (missing links), due to decomposition of some part(s) or whole organisms, being scavenged upon, unavailability of suitable conditions for fossilization and only a few have been discovered.(ii) Distortion of parts during sedimentation – which may give wrong impression of structures.(iii) Destruction of fossils by geological activities e.g. earthquakes, faulting, uplifting and mass wasting.
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