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PHYS 0106 (Spring, 2001) Earth History Timeline |
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| Proterozoic Eon: Neoproterozoic | |||
Timeline Links Phanerozoic Neoproterozoic Mesoproterozoic Paleoproterozoic Archean Other Links Historical Geology Page Physical Geology Page Mike's Home Page |
Writer/Researcher: Joe Cronin Editor: Mike Boyd Web Page Builder: Joe Cronin The evolution of mineral-based hard parts was an important step in the evolution of life. It was also an important step for our understanding of life. Because of these new mineral-based hard parts the fossil record improved tremendously. This made it so scientists could study the fossilŐs physical forms in hopes of divining from their bone structure the way in which these creatures might have lived. For about a century geologists believed that there was no fossil record before these hard parts occurred, therefore many believed that there was no life before the Cambrian Period. ThatŐs why the development of shells and other mineral-based hard parts became the dividing point between the Cambrian and the Pre-Cambrian Periods. Scientists can still not explain why hard parts first developed or why they developed as rapidly as they did. Because of this scientists have come up with many explanations in attempting to solve one of natureŐs great puzzles. One thing that scientists do agree on is that the adaptation of mineral-based hard parts was a global event therefore a global change must have occurred. The change may have happened because the oxygen concentration in the ocean reached a point where there was enough oxygen and animals could create these mineral-based hard parts. The hard parts would restrict the oxygen intake, but there was still enough oxygen available to allow respiration in spite of this restricted access to the oxygen. Another possibility is that the hard parts were a response to the predator prey relationship in multi-cellular animals. Some of the evidence for this comes from the tubular cells called Cloudina. These, as far as we know, were the first mineral-based hard parts developed by animals. Some specimens found in the late Pre-Cambrian Period have holes in them. Scientists believe these holes to be evidence of an attack by some yet to be discovered ancient predator. This is hard to verify since the predators of this time period were generally not preserved. The truth is that we do not know what caused the evolution of mineral-based hard parts, but because of its complexity the above events as well as other factors probably played a role in their development. It would be hard to believe that one single thing could cause such a large event.
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