Life on Land

Life on Land - Life on Land Forbillionsofyears,...

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Life on Land For billions of years, the only life present on earth existed in the nutrient environments of the oceans,  lakes, and rivers. About 600 million years ago, the Paleozoic Era began. Scientists believe that living  things first came to occupy the land during this era. They also believe that during a subdivision of the  Paleozoic Era called the Cambrian Period, the main groups of marine invertebrates in existence  today evolved. A so-called “Cambrian explosion” occurred. The appearance of multicellular  organisms is notable in the Cambrian Period, when evolution and natural selection led to a vast array  of organisms filling every conceivable niche on the earth. Many organisms that arose at that time  have since become extinct. After the Cambrian Period came the Ordovician Period. In the Ordovician Period, wormlike animals  with stiff rods along their backs came into being. These organisms are now called 
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This note was uploaded on 11/11/2011 for the course BIO 101 taught by Professor Pesthy during the Fall '07 term at Texas State.

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Life on Land - Life on Land Forbillionsofyears,...

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