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posdef1 Teacher
High School - 9th GradePosted by posdef1 on Thursday December 10, 2009 at 6:02 AMChallenges included the variability of water availability, the variability of temperature, and the presence of ultraviolet radiation. In the oceans, there is large stability of temperature, at least within seasons, water is of course always available, and that water absorbs the natural ultraviolet rays from the Sun. On land, when the first land plants appeared, the ozone layer had yet to form, making the land a hostile environment. These factors are why life began in the ocean.
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versatilekamini Teacher
DoctorateeNotes Editor
Posted by versatilekamini on Thursday December 10, 2009 at 8:36 AMThe first plants were algae and these still thrive in aquatic habitats today.They are small autotrophic plants that fail to reach any cellular differentiation and their sex organs are unicellular and, if they are multicellular, all cells are fertile.
The basic challenges which life on earth present to plants that their algal ancestors did not face include desiccation of plants caused by growing shortage of water,uv radiation caused by nuclear explosions and the resultant increase in temprature due to global warming.
