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GEOLOGIC TIME James Ussher concluded that Earth was only FOUR THOUSAND YEARS OLD Catastrophism Earth's landscapes had been developed primarily by great catastrophes Modern Geology Introduced the principle of UNIFORMITARIANISM The process we observe presently now have always been operated in the past. "The present is the key to the past" James Hutton Relative Dating determining relative order in the past without necessarily determining their age placing rocks and events in sequence Principles and rules Law of Superposition Principle of Original Horizontality Cross-cutting Relationship Law of Inclusion Unconformities Law of Superposition oldest rocks are at the bottom Youngest Oldest Principle of Original Horizontality Cross-cutting Relationship younger features that cuts across through a sequence an older feature any feature that cuts across a sequence of rock, is younger than everything it cuts Law of Inclusions pieces of one rock unit that are contained within another Unconformities a break in the rock record represent the long period during which deposition ceased, erosion removed previously formed rocks, then deposition resumed. Types of Unconformities Angular Unconformity Disconformity Nonconformity Angular Unconformity is an erosional surface on tilted or folded strata, over which younger strata have been deposited Disconformity A surface of erosion or non-deposition between Parallel sedimentary rock beds of differing ages Nonconformity is an erosional surface on igneous or metamorphic rocks which are overlain by sedimentary rocks. Correlation of Rock Layers Matching rocks of the same age in different regions. End . . . Fossils: Evidence of past life • Arien P. Avenasa • Remains or traces of prehistoric life • Important basic for interpreting the geologic past Paleontology vs. archeology • Paleontologists study fossils and are concerned with all lifeforms in the geologic past. By contrast, archaeologists focus on the material remains of past human life. (i.e. sites, buildings, artifacts) Paleontologist = geology + biology succession of life over the vast expanse of geologic time Type of fossils • Unaltered remains • Petrified (literally, “turned into stone”) • Replacement • Molds and Casts • Carbonization • Amber • Tracks • Burrows • Coprolites • Gastroliths Under what circumstances are they preserved? • Rapid burial (the remains are buried by sediment. When this occurs, the remains are protected from the environment, where destructive processes operate. Therefore, rapid burial is an important condition favoring preservation.) • Possession of hard parts. (Hard parts such as shells, bones, and teeth predominate in the record of past life.) principle of fossil succession • (Fossil organisms succeed one another in a definite and determinable order; and therefore any time period can be recognized by its fossil content.) • Index fossils - these fossils are widespread geographically and are limited to a short span of geologic time, so their presence provides an important method of matching rocks of the same age. Basic atomic structure Protons = positive charge Neutron = neutral Electron = negative charge Alpha Emission Radioactivity Beta Emission Electron Capture Three types of radioactive decay • ATOMIC NUMBER: number of protons in the nucleus • ATOMIC MASS NUMBER: protons + neutrons RADIOACTIVITY CALCULATING THE AGES OF ROCKS AND MINERALS THAT CONTAIN PARTICULAR RADIOACTIVITY ISOTOPESDECAYING AT A FIXED RATE SINCE THE FORMATION OF THE ROCKS PRODUCTS OF DECAY HAVE BEEN ACCUMULATING AT A CORRESPONDING RATE A CORRECT DATE IS NOT POSSIBLE UNLESS THERE WAS NEITHER THE ADDITION NOR LOSS OF PARENT OR DAUGHTER ISOTOPES. ADIOCARBON DATING • TO MEASURE RECENT EVENTS • HALF LIFE OF CARBON – 14 IS ONLY 5,730 YEARS, IT CAN BE USED FOR DATING EVENTS FROM THE HISTORIC PAST AS WELL AS THOSE FROM VERY RECENT GEOLOGIC HISTORY. • CARBON -14 Carbon- 14 is continuously produced in the upper atmosphere as a consequence of cosmic-ray bombardment. THE END The Geologic Time Scale by: Yves Mariene L. Dela Peña Geological Time Scale • Divides Earth's history into units of varying magnitude. • Used by scientist to describe the timing and relationships between events that have occured during the history of Earth. Structure of the Time Scale • Eons- represent the greatest expanses of time. • Phanerozoic- a term Derived from the Greek words meaning "visible life." • -contain abundant fossils that document major evolutionary trends Three eras within the Phanerozoic: • Paleozoic (ancient life), Mesozioc (middle life), and Cenozoic (recent life) • Each era of Phanerozoic econ is subdiveded into periods • Each periods is divided into smaller units called epochs The Geologic Time Scale Quaternary Latin, “fourth” 1822 Tertiary Latin, “third” 1760 Cretaceous Latin creta, “chalk” 1822 Jurassic Jura Mountains, Switzerland 1795 Triassic Latin, “three-fold” 1834 Permian Perm, Russia 1841 Carboniferous Carbon-bearing 1822 Devonian Silurian Devonshire, England Silures, a pre-Roman tribe 1840 1835 Ordovician Ordovices, a pre-Roman tribe 1879 Cambrian Latin Cambria, “Wales” 1835 Precambrian Time • Precambrian- represent about 88 percent of Earth history • 4 billions years prior to the Cambrian is divided into three econs: • Hadean • Archean • Proterozoic Terminology and the Geologic Time Scale • Precambrian- the informal name for the econs that came before the current Phanerozoic econ. • Hadean- is another infromal term that is found on some versions of the geologic time scale and is used by some geologists. Difficulties in Dating the Geologic Time Scale • Samples of sedimentary rock can only rarely be dated directly by radiometric means. The rock's age cannot be accurately determined because the grains making up the rock are not the same age as the rock in which they occur. Rather,the sediments have been weathered from rocks of diverse ages • Radiometric dates obtained from metamorphic rocks may also be difficult to interpret because the age of a particular mineral in a metamorphic rock does not necessarily represent the time when the rock initially formed. Instead, the date may indicate anyone of a number of subsequent metamorphic phases. • Dendrochronology-The dating and study of annual rings in trees • Cross dating- by matching the ring pattern common to both sample. • Tree-ring –chronologies are unique archieves of environmental history and have important applications in such disciplines as climate, geology, ecology and archaeology. Weather which encourages narrow treering growth Weather which encourages wide tree-ring growth Harsh winter mild winter Hot summer mild summer drought wet summer Is Earth Unique? There is only one place in the universe, as far as we know, that can support life—a modest-sized planet called Earth that orbits an average-sized star, the Sun. The Right Planet Its force of gravity would be proportionately greater. Like the Moon and Mercury, both of which lack an atmosphere, Earth would be void of life. The entire planet would likely he covered by an ocean a few kilometers deep. The fact that if our planet did not have a molten metallic core, most of the lifeforms on Earth would not exist. The Right Location 10 percent closer to the Sun, like Venus, our atmosphere would consist mainly of the greenhouse gas carbon dioxide. 10 percent farther from the Sun, the problem would be reversed—it would be too cold. Near a star of modest size. Stars like the Sun have a life span of roughly 10 billion years. The Right Time Microorganisms evolved that released oxygen into the atmosphere by the process of photosynthesis. Habitats, along with evolutionary forces, led to the development of many large mammals that occupy our modern world. Birth of a Planet Big Bang theory - formation of our planet began about 13.7 billion years ago with a cataclysmic explosion that created all matter and space. Big Bang scenario, atoms in your body were produced billions of years ago in the hot interior of now defunct stars, and the formation of the gold in your jewelry was triggered by a supernova explosion that occurred trillions of miles away. From Planetesimals to Protoplanets Solar nebula Planetesimals Protoplanets Earth's Early Evolution Formation Of Early Earth Origin of the Atmosphere and Oceans • By: Sabellano The air we breathe is a stable mixture of 78% nitrogen, 21% oxygen, about 1%argon (an inert gas), and small amount of gases such as carbon dioxide and water vapor. Earth’s Primitive Atmosphere Early in the Earth’s formation, it consisted of gases like hydrogen, helium, methane, ammonia, carbon dioxide and water vapor. Hydrogen and helium are the lightest of these gases. Earth’s gravity was too weak to hold those light gases. Most of the gases were probably scattered into space by strong solar winds from a young active sun. Earth’s first enduring atmosphere was generated by a process called outgassing. In which gases trapped in the planet’s interior are released. Oxygen in the Atmosphere During this period of intense, Earth became hot enough that iron and nickel began to melt. Occurs rapidly on the on the scale of geologic time and produced Earth’s dense ironrich core. This period differentiation established the three major division’s of Earth’s interior: rich core, the thin primitive crust, and the Earth’s thickest layer, the mantle. Evolution of the Oceans Precambrian History: The formation of Earth's Continents Precambrian History The Precambrian History, which is divided into the Archean and Proterozoic eons, spans almost 90% of Earth’s history. Much of Earth’s stable continental crust was created during this time The Archean is the name of the age which began with the forming Earth. Following the Hadean Eon and preceding the Proterozoic Eon. During the Archean, the earth's crust and layers had just formed, making the Earth much cooler than it was during the Hadean and allowing the formation of continents. The Proterozoic is a geological eon representing the time just before the proliferation of complex life on Earth. The name Proterozoic comes from Greek and means "earlier life", the Greek root protero ,means "former, earlier" and zoic- ,means "animal, living being". is the most recent part of the Precambrian. Precambrian History Partial melting of the mantle formed volcanic islands arc and ocean plateaus. These crustal fragments collided and accreted to form larger crustal provinces . Precambrian History Larger crustal areas were assembled into larger blocks called cratons. Cratons form the core of modern continents. Precambrian History Supercontinents Large landmasses that consist of all , or nearly all, existing continents. Pangaea was the most recent, but perhaps and even larger one, Rodinia, preceded it. Splitting and reassembling of supercontinents have generated most of Earth’s major mountain belts. Supercontinents have also profoundly affected Earth’s climate over time. PANGEA Rodinia Geologic History of the Phanerozoic: Formation of Earth’s Modern Continents Ebal, Queennie Joy J. PHSC 9:00-10:30 TTH Phanerozoic Era - The time span since the close of the Precambrian period - Encompasses 542 million years and is divided into 3 eras: Paleozoic Mesozoic Cenozoic - The study of Phanerozoic crustal history was aided by the availability of fossils, which improved our ability to date and correlate geologic events. First life-forms with hard parts such as shells, scales, bones, or teeth—all of which greatly enhance the possibility of an organism being preserved in the fossil record Paleozoic History - North America hosted no living things - The continent was largely a barren lowland - One of the major events was the formation of the supercontinent: PANGAEA Formation of Pangaea - began with a series of collisions that gradually joined North America, Europe, Siberia, and other smaller crustal fragments LAURASIA - large northern continent GONDWANA encompassed five continents-—South America, Africa, Australia, Antarctica, India and perhaps portions of China Mesozoic History Spanning about 186 million years, the Mesozoic era is divided into three periods: the Triassic primarily red sandstones and mudstones that lack marine fossils Jurassic extensive continental sediments were deposited Cretaceous formation of "coal swamps” similar to those of the Paleozoic era Navajo Sandstone, a crossbedded, quartz-rich layer, that in some places approaches 300 meters (1,000 feet) thick. Cenozoic History Era of Recent Life - encompasses the last 65.5 million years of Earth history - the rock formations are more widespread and less disturbed than those of any preceding era. - Volcanic activity was also common in the West during much of the Cenozoic. - The effects of mountain building, volcanic activity, isostatic adjustments, and extensive erosion and sedimentation created the physical landscape we know today. HOW DID LIFE BEGIN? REQUIREMENTS OF LIFE: - Presence of hospitable environment - Chemical raw materials that form the essential molecules of DNA, RNA, proteins - Amino Acids Prokaryotes – 1st known organisms Anaerobic Metabolism – without oxygen Cyanobacteria – contributed rise of oxygen Stromatolites – fossil evidence of these bacteria Eukaryotes – multicellular organisms Paleozoic Era – emergence of a spectacular variety of new life-forms Quaternary Period – humans evolved, actions of glacial ice, wind and running water added the finishing touches