Plant Evolution

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Submitted By colette36
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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 would have been enormously important in the colonization of land. In this zone algae would have been exposed to fresh water running off the land (and would have colonized the freshwater habitat before making the move to terrestrial existence). They would also be exposed to an alternating wet and desiccating environment. Adaptations to survive drying out would have had strong survival value, and it is important to note that seaweeds are poikilohydric and able to withstand periods of desiccation (The University of the West Indies. Department of Biological and Chemical Sciences 2003-2012).
The earliest evidence for the appearance of land plants, in the form of fossilized spores, comes from the Ordovician period (510 - 439 million years ago), a time when the global climate was mild and extensive shallow seas surrounded the low-lying continental masses. These spores were probably produced by submerged plants that raised their sporangia above the water - wind dispersal would offer a means of colonizing other bodies of water. However, DNA-derived dates suggest an even earlier colonization of the land, around 700 million years ago (The…...

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