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Notes – Early Earth History Chapter 8 Section 2 Life on Earth Changes Paleontologists discovered that the system used to _____________________ modern organisms could be used to classify _____________________. Fossils from rock layers that are touching are more _____________________ than fossils from widely separated layers. The more recent a fossil was formed, the more it _____________________ a living organism. Precambrian Time Precambrian rocks are difficult to study because they have undergone _____________________ or been destroyed. Precambrian fossils are not abundant but provide a lot of information about Earth’s early _____________________ and _____________________. The Precambrian Atmosphere Archean _____________________ contain large amounts of pyrite and uraninite. Today’s atmosphere contains _____________________ that quickly destroys these minerals through _____________________. Earth’s early atmosphere had very _____________________ oxygen. Ozone The absence of oxygen suggests there was no _____________________ layer during _____________________ time. Without ozone, ultraviolet rays cause death or _____________________ in cells. Changes in one gene in an organism could result in _____________________ life forms many generations later. The First Organisms Cyanobacteria—one of the _____________________ organisms. Stromatolites are mounds of alternating thin-layered sediments and _____________________ cyanobacteria that take in carbon dioxide and release _____________________. A Changing Environment Oxygen levels _____________________ slowly as _____________________ and other earlylife forms released oxygen. Natural _____________________ favored organisms that could tolerate or use _____________________. The amount of ozone in the atmosphere _____________________. Soft-Bodied Organisms The first invertebrate organisms—animals _____________________ backbones—appeared during the _____________________ eon. o Ediacaran fauna The Paleozoic Era The first appearance of fossils of organisms made from _____________________ parts marks the end of the Proterozoic eon. Because hard parts fossilize easier, fossils are easier to find in _____________________ rocks than Precambrian rocks. The Cambrian Explosion During a relatively short period of time, the number of animals with _____________________ greatly _____________________. Invertebrates—sponges, jellies, _____________________—also evolved during the _____________________ explosion. Invertebrates of the Paleozoic Era Throughout the Paleozoic era, the oceans contained a wide variety of _____________________ organisms. Corals, brachiopods, crinoids, bryozoans Ordovician period, Silurian period Vertebrates of the Paleozoic Era Vertebrates—animals _____________________ backbones—evolved during the early Paleozoic era. The first of these lived in the _____________________. o Bony fish with bony rays that supported their fins o Bony fish with thick fins supported by large _____________________ and muscles A New Egg A new organism that could lay its _____________________ on land evolved during the early _____________________ period. Amniotes laid water-tight, amniotic eggs and could spend all their time on _____________________. o Mammals, _____________________, and reptiles evolved from amniotes. Plants of the Paleozoic Era During the Ordovician period, _____________________ began spreading onto land. Early land plants were small and lived in _____________________ areas because they could not move water to all their parts. Plants with _____________________ systems that could move nutrients between roots and leaves then evolved. o New plants _____________________ quickly. Paleozoic Extinctions The Paleozoic era ended with the late _____________________ extinction— _____________________ of marine and 70% of _____________________ species. The uplifting formation of _____________________, or ash and _____________________ released from the Siberian Traps may explain the Permian extinction.