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Geologic Time Geologic Time • The first geologic time scale was proposed in 1913 by the British geologist Arthur Holmes (1890 - 1965). This was soon after the discovery of radioactivity, and using it, Holmes estimated that the Earth was about 4 billion years old - this was much greater than previously believed. The Divisions of Precambrian Time Precambrian Era • 4.6 billion years ago, the Earth was born. • Nearly 4 billion years passed after the Earth's inception before the first animals. This stretch of time is called the Precambrian. • It makes up roughly seven-eighths of the Earth's history • During the Precambrian, the most important events in biological history took place. Precambrian Era • The Earth formed, life arose, the first tectonic plates arose and began to move, eukaryotic cells evolved, the atmosphere became enriched in oxygen -- and just before the end of the Precambrian, complex multicellular organisms, including the first animals, evolved. Precambrian Earth Precambrian Era • Also divided into different Eons: –Hadean – Earths creation –Archean – Earliest Rocks form –Proterzoic - First organisms with well-developed cells form. Paleozoic Era Divisions Paleozoic – “Ancient Life” The Paleozoic Era • At its beginning, multi-celled animals underwent a dramatic explosion in diversity, and almost all living animal phyla appeared within a few millions of years. • At the other end of the Paleozoic, the largest mass extinction in history wiped out approximately 90% of all marine animal species. The causes of both these events are still not fully understood Paleozoic Era • The Paleozoic took up over 300 million years. • During the Paleozoic there were six major continental land masses. • These Paleozoic continents experienced tremendous mountain building along their margins, and numerous incursions and retreats of shallow seas across their interiors. Gondwana and the Continental Landmasses During Paleozoic Period Cambrian Period • "Age of Trilobytes" -The Cambrian Explosion of life occurs; all existent phyla develop. Many marine invertebrates • First vertebrates. Earliest primitive fish. Mild climate. • Mass Extinction of trilobites and nautiloids at end of Cambrian (50% of all animal families became extinct), probably due to glaciation. The Cambrian Sea Ordovician Period Ordovician Period • First corals. • Primitive fishes, seaweed and fungi. Graptolites, bryozoans, gastropods, bivalves, and echinoids. • High sea levels at first, global cooling and glaciation, and much volcanism. • North America under shallow seas. Ends in huge extinction, due to glaciation. Silurian Period Silurian Period • Primitive plants appear on land. • The first jawed fishes • First vascular plants (plants with waterconducting tissue) appear on land • High seas worldwide. Brachiopods, crinoids, corals. • First insects appeared. Devonian Period – Age of Fishes Devonian Devonian Period "The Age of Fishes" • Fish and land plants become abundant and diverse. • First amphibians appear (evolved from the lungfish). First sharks, and bony fish. • Many coral reefs, brachiopods, crinoids. • New insects appeared. • Mass Extinction (345 mya) wiped out 30% of all animal families) probably due to glaciation or meteorite impact Carboniferous Period Carboniferous Period (Mississippian & Pennsylvanian) • Wide-spread coal swamps and many ferns. • Appalachian Mountains form. • Amphibians become more common. • First true reptiles. • The first cockroaches appear • First winged insects Model of a Pennsylvanian Coal Swamp Mountains formed during this period Amphibians of the Permian Period Permian Period "The Age of Amphibians" • Amphibians and reptiles dominant. • Gymnosperms dominant plant life. • The continents merge into a single supercontinent, Pangea. • Phytoplankton and plants oxygenate the Earth's atmosphere to close to modern levels. • The Permian ended with largest mass extinction. Trilobites go extinct, as do 50% of all animal families, 95% of all marine species, and many trees, perhaps caused by glaciation or volcanism Late Paleozoic Plate Movements Mesozoic Era 245 – 208 MYA Mesozoic Era • The Mesozoic is divided into three time periods: – the Triassic (245-208 Million Years Ago), – the Jurassic (208-146 Million Years Ago), – and the Cretaceous (146-65 Million Years Ago). • Mesozoic means "middle animals", and is the time during which the world fauna changed drastically from that which had been seen in the Paleozoic. Mesozoic Era • Dinosarus, evolved in the Triassic, but were not very diverse until the Jurassic. • Except for birds, dinosaurs became extinct at the end of the Cretaceous. • The Mesozoic was also a time of great change in the terrestrial vegetation. The early Mesozoic was dominated by ferns, cycads • Modern gymnosperms, such as conifers, first appeared • By the middle of the Cretaceous, the earliest angiosperms had appeared Mesozoic Plant Life Dinosaurs of the Triassic Period Triassic Period • The first dinosaurs, mammals, and crocodiles appear. • Mollusks are the dominant invertebrate. • Many reptiles, for example, turtles. • True flies appear. • Triassic period ends with a minor extinction 213 mya (35% of all animal families die out, including marine reptiles). This allowed the dinosaurs to expand Jurassic Period Jurassic Period • • • • Many dinosaurs, including the giants. The first birds appear (Archaeopteryx). The first flowering plants evolve. Many ferns, cycads, gingkos, rushes, conifers, • Flying reptiles, pterosaurs. • Minor extinctions at 190 and 160 mya. Earth During the Jurassic Period Life of the Cretaceous Period Cretaceous Period • The heyday of the dinosaurs. • The earliest-known butterflies appear as well as the earliest-known snakes, ants, and bees. • High tectonic and volcanic activity. • Primitive marsupials develop. • Continents have a modern-day look. • Ended with large extinction (the K-T extinction) of dinosaurs, pterosaurs, ammonites, about 50 percent of marine invertebrate species, etc., probably caused by asteroid impact or volcanism. What happened to the dinosaurs? Asteroid? Volcanoes? Glaciers? Cenozoic Era 65 MYA to Present Cenozoic Era the Age of Mammals Cenozoic Era • The Cenozoic is the most recent of the three major subdivisions of animal history. • The Cenozoic is called the Age of Mammals, because the largest land animals have been mammals during that time. • The Cenozoic is divided into two main sub-divisions: the Tertiary and the Quaternary. Tertiary Mammals Tertiary Period • First large mammals and primitive primates, • Mammals abound. Rodents appear. Mammals return to the sea. • Flower plants thrive. • More mammals, including the horses, dogs and bears. Modern birds. • First hominids (australopithecines). • Continental glaciers repeatedly cover NA Quaternary Period • The first humans (Homo Sapiens) evolve. Mammoths, mastodons, saber-tooth tigers, giant ground sloths. • A mass extinction of large mammals and many birds happened about 10,000 years ago, probably caused by the end of the last ice age. • Human civilization Early Man – Quaternary Period Geologic Time Scale of Kentucky Bluegrass Geology The bedrock in the center (Bluegrass Region) of the State is composed of limestones and shales from the Ordovician Period (510 to 440 million years ago). The oldest rocks at the surface in Kentucky are limestones from the Late Ordovician Period (approximately 450 million years ago), which are exposed along the Palisades of the Kentucky River (for example, near Camp Nelson, in Jessamine County, pictured above). Ordovician fossils are abundant in many areas.