One's personality is both a composition and reflection, but if I have to choose one of them, I will choose reflection as the "self" is more important to me than "me". One's composition may change, walking across the cultural landscapes and climbing the social ladder but one's self is tied to one's reflections. The fun part is that reflections are not bound to "Time-Space" barriers ( it is not time-space) and respective mental constructs, which have grown so thick over ages, that they had reduced the image of humans to Sisyphus, rolling different sizes of boulders on hills of different heights.… As the name of this Blog indicates, knols are my perspectives on topics of interests, sweet/bitter experiences or just doodling :)
Monday, November 28, 2011
Fossil Records and Evolution
Fossils are the most reliable evidence of evolution. Fossils along with strata of sedimentary rocks and radioactive minerals have not only recorded the history of earth but also the history of life. We know that earth’s crust is dynamic and they change regularly through tectonic forces and related magmatism, metamorphism and sedimentary processes. Tectonics not only changes the continents and oceans but also because cycling of rocks and in these processes a large portion of the earth history is destroyed as old layers are consumed and new layers are produced. It is noteworthy that oceanic crust is quiet young, younger than Dinosaurs (Tertiary age). Despite of dynamic nature of earth crust and also rarity of preservations of life to become fossil, sedimentary rocks bear enough fossils record that we could trace back the history of life.
Unlike, mutation, genetic flow, genetic drift and sex and recombination which are provide mechanisms of evolution but sometimes with controversies, the fossil record is clear and evident. As move back into older rocks, we can’t find evolved organisms. Fossils records unveil organisms that lived once but are extinct now. Everybody knows about Dinosaurs and a large number of people know of complete extinction of Trilobites.
Cyanobacteria are amazing organisms that are able to fix Atmospheric Carbon and Nitrogen. All photosynthetic plants can fix atmospheric carbon dioxide but can’t fix nitrogen and they need the help of nitrogen fixing bacteria. Cyanobacteria bear a blue photosynthetic pigment. Cyanobacteria got their name from this bluish pigment. Cyanobacteria uses water as an electron donor and it is why they live in oceans, Saline waters and fresh lakes and also in damp soil and rock surfaces. As oxygen is by-product of photosynthesis so Cyanobacteria played a vital role in changing the composition of earth’s atmosphere by making free oxygen available in atmosphere.
Some of the Cyanobacteria construct structures known as stromatolite. Stromatolites are formed by layers upon layers of Cyanobacteria mesh work which trap sediments in them. Once a layer dies, the next layer grows on it and so layers upon layers are deposited over years. They can be of different shapes, stratiform, conical, domal and even branching. Shark Bay of Western Australia is very famous for stromatolites and the process of stromatolite still going on.
Stromatolite is important in fossil record as they make the oldest known fossil record. Stromatolites from Warrawoona Group in Western Australia are 3.5 billion years old. Similarly Fig Tree Group of South Africa possesses Stromatolites that are relatively of younger age, 3.4 billion years old. Stromatolites are significant records as they are the first evidence of life on earth. As Cyanobacteria is of 3.5 billion years old and still exist and it is an amazing phenomenon as we will notice later that a lot of life forms that evolved later disappeared from face of earth by what we know as extinction.
Cherts are microcrystalline rocks or rocks layers that can be of sedimentary or hydrothermal origin. Unicellular organisms like radiolarian and diatoms bear siliceous shells. Both Radiolarian and Diatoms are planktonic unicellular organism means they float on water. When these organisms die, their shell sink and deposit on the bottom of ocean or lake and over thousands or millions of years create radiolarian or diatomaceous Chert deposits.
Geysers are springs of hot water that is the result of trapped magmatic bodies underground. Geysers are mineral rich. If a geyser is silica rich, the results of its deposits may be as Chert and it is called hydrothermal Chert. Rhynie Chert is Scotland is very famous for its highly detailed preserved, fossils.
Gunflint Chert is 2 billion years old Chert of Gunflint of North America. It is Banded iron Chert which is important not only because they preserve microfossils but because they tell us of alternate cycles of oxygenated water and deoxygenated water bodies in which these Cherts and iron shale have deposited.
This knol is still under construction..........