 Section 8 The Cambrian Explosion and the Diversification of Animals ail&mid=C3A2C5658B8D5136EF42C3A2C5658B8D5136EF42 Video: The Cambrian Explosion 1 and 2 l&mid=0AC37412BD6F51346B420AC37412BD6F51346B42 VQFRVP#view=detail&mid=2F1903F0B417DD5E13772F1903F0B417DD5E1 377 The Cambria Explosion Song

59.The first evidence of multicellular animals appears in fossils from about 575 million years ago,after the last snowball glaciation. 60.List four types of organisms thought to be some of the first multicellular animals. worms, jellyfish, sea pens, and polyps worms, jellyfish, sea pens, and polyps

61. Within 50 million years every major animal phylum known in fossil records quickly appeared during what is known as the Cambrian Explosion.

62.What triggered the Cambrian Explosion? Scientists have pointed to many factors. List 4 examples from the reading. 1.The development of predation probably spurred the evolution of shells and armor 2.the growing complexity of ecological relationships created distinct roles for many sizes and types of organisms. 3.Rising atmospheric and oceanic oxygen levels promoted the development of larger animals 4.Some scientists believe that a mass extinction at the end of the Proterozoic era created a favorable environment for new life forms to evolve and spread.

63.Land plants emerged between about 500 to 400 million years ago. 64.Once plants were established, what 4 roles did plants serve? 1.stabilized soil against erosion 2.accelerated the weathering of rock by releasing chemicals from their roots. 3.reduced the greenhouse effect and cooled Earth's surface. 4.By creating shade, they also provided habitat for the first amphibians to move from water to land.

65. Though scientists do not understand what caused the most severe of all mass extinctions, scientists believe an estimated 80 to 85 percent of all living species were wiped out. 66.Geologic records indicate that deep seas became anoxic, which suggest that something interfered with normal ocean mixing, and that Earth's climate suddenly became much warmer and drier. 67. Possible causes for these developments include massive volcanic eruptions or a melting of methane deposits (huge reservoirs of solidified methane), both of which could have sharply increased the greenhouse effect.

68.The Mesozoic era was the era of reptiles, which colonized land and air more thoroughly than the amphibians that preceded them out of the water. 69.Dinosaurs evolved about 215 million years ago, and became the largest and most dominant animals on Earth for the next 150 million years. This period also saw the emergence of modern land plants, including the first angiosperms (flowering plants); small mammals ; and the first birds, which evolved from dinosaurs.

70.Another mass extinction 65 million years ago, killed all of the dinosaurs except for birds, along with many other animals. 71.Scientists published a theory that a huge meteorite had hit Earth causing the last mass extinction. What do scientist think were 3 results of this impact? Scientist believe this hit would have caused 1) impact like shockwaves, 2) severe atmospheric disturbances, and a 3) global cloud of dust that would have drastically cooled the planet.

72.Scientist’s most important evidence was widespread deposits of iridium —a metal that is extremely rare in Earth's crust but that falls to Earth in meteorites. 73.Discuss the further evidence discovered since 1980 that supports the meteor theory. A crater has been identified on Mexico's Yucatan peninsula, that could have been caused by a meteorite big enough to supply the excess iridium, and grains of shocked quartz from the Chicxulub region have been found in sediments thousands of kilometers from the site that date to the boundary era.