Essay about Plant Evolution

1545 Words Nov 16th, 2012 7 Pages
PLANT EVOLUTION

Plant Evolution

Colette Andrews
Strayer University

SCI 115
Dr. David Davies
November 24, 2012

Plant Evolution has been around for millions of years. In fact, plants were the first species on earth and the first to live on land (“Plant Evolution”, D. Davies, accessed 11/24/12). For 1500 million year’s photosynthetic organisms remained in the sea. This is because, in the absence of a protective ozone layer, the land was bathed in lethal levels of UV radiation. Once atmospheric oxygen levels were high enough the ozone layer formed, meaning that it was possible for living things to venture onto the land (The University of the West Indies. Department of Biological and Chemical Sciences 2003-2012). The seashore
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If it was not for plants we would not have clean, breathable air ((“Plant Evolution”, D. Davies, accessed 11/24/12). Plants also cover and alter most terrestrial habitats, controlling water and sediment movements (“Plant Evolution”, D. Davies, accessed 11/24/12). Plants have produced all of the food for (nearly) every organism for all geologic times (“Plant Evolution”, D. Davies, accessed 11/24/12).
The Cyanobacteria (blue-green algae) are a group of prokaryotes that are extremely important both ecologically (especially in global carbon and nitrogen cycles) and evolutionary terms. Stromatolites, which are formed by cyanobacteria, provide living and fossil evidence of cyanobacteria going back 2700 million years. Today stromatolites grow only in shallow, salty pools in hot, dry climates (e.g. Shark Bay in Western Australia), and their abundance in ancient rocks implies similar environmental conditions in those times (University of California Berkeley, Mus. Paläont). Stromatolites and other cyanobacteria were the main contributors to the marked increase in atmospheric oxygen concentrations that began around 2000 million years ago. Today, cyanobacteria are found everywhere - in marine, freshwater and terrestrial environments and as symbionts e.g. lichen - and contribute up to 50% of the atmosphere's oxygen (University of
California Berkeley, Mus. Paläont). Poikilohydry means that the organism relies directly on the environment for

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