Biology : Semester II


IntroductionSection 1 | Section 2 | Section 3 | Section 4 | Section 5

  Section Three:

Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 | Part 9 | Part 10 | Part 11 | Part 12 | Part 13 | Part 14

Biology : The Time of Ancient Life : Part One

The Paleozoic:
The Time of Ancient Life

The Paleozoic Era literally translates as the "time of ancient life".  It spans the time between the end of the precambrian 544 million years ago and the beginning of the Mesozoic Era 245 million years ago. The Paleozoic is the first of three eras within the Phanerozoic Eon (the time of visible life). Life originated during the early part of the precambrian and increased in complexity and diversity during the later precambrian.  The Paleozoic Era saw by the evolution of animals with hard preservable parts such (shells and exoskeletons). This has led to what is popularly known as the Cambrian Explosion, the sudden appearance of a stupendous array of animal life, much of which is not closely related to modern forms. Despite extinctions at various times, the Paleozoic is notable for the increasing modernization of life. By the end of the Paleozoic, almost all major groups of life had developed. The Paleozoic ended in the greatest mass extinction event in world history: the Permian extinction. During this massive die-off nearly 96% of all marine species went extinct. The cause of this greatest catastrophe in Earth history has been much investigated and scientific consensus of its cause has yet to emerge.

During the Paleozoic we see several major advances in life. The Cambrian Explosion is the first. The evolution of plants from some group of green algae during the Ordovician is another, since these plants moved from water onto land, paving the way for vertebrate animals to follow. The first vertebrates, amphibians, were little more than legged fish, although their remote descendants would come to rule the land as reptiles, the first truly terrestrial vertebrates.
The Paleozoic era is subdivided into (in order from oldest to youngest) the Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian periods. Outside North America, the Mississippian and Pennsylvanian are combined to for the Carboniferous period.

The Physical Setting

Geologically, the Paleozoic is noted for the assembly of Pangaea, the supercontinent proposed in the 1912 book The Origin of Continents and Oceans by German meteorologist Alfred Wegener (1880-1930) as part of his continental drift hypothesis.

Alfred Lothar Wegener, the visionary German scientist whose continental drift ideas would form a major part of the modern theory of plate tectonics.
Pangaea at its height during the later Paleozoic

The quick and dirty explanation of plate tectonics is that the Earth’s crust is made of various-sized plates. These are in motion relative to each other, although usually a rate of at most a few inches per year. Continents are parts of these plates. Over time as the plates move the continents move as well.

Dynamic Earth Lab Notebook: 10 points

This Dynamic Earth: The Story of Plate Tectonics. This is an online version of a U.S. Geological Survey (USGS) publication that gives a well-illustrated account of the development and implications of plate tectonic theory. To familiarize yourself, visit the site and then write your own summary of the theory of plate tectonics.

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