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Earth’ss History… Earth History… • The The earth has a history much like human earth has a history much like human civilization has a history. – Major events Major events – Distinctions of time – Periods of lost time Periods of lost time – Distinct cultures • Rather than on paper the Earth’s history is written in the rocks. Uniformitarianism….. • The present is the key to the past… • The events of today have always taken place. 2.9 Billion Years Ago Today Geologic Timescale… • Human History is compiled in books – Earth’s history is compiled in the rocks…. • Geologic Timescale.. Earth’s Age ‐Apx. 4.6 billion years – Events are placed in chronological order and grouped into Eons Eras Periods Epochs Eons, Eras, Periods, Epochs … – Each grouping is marked by distinct major events and ages in m.y.a (millions of years ago) are given…. – The timescale is a living document. Meaning the groupings, events and times are based on our most current knowledge and are constantly changing knowledge and are constantly changing…… • Geologic Timescale – g A summary of the major events in y j Earth’s history is based on living things (fossil evidence). How do scientist divide geologic time ????? time ????? • Fossil Record ……. Fossil Record ……. 4 Major Time Scale Divisions…. 4 Major Time Scale Divisions…. • Eons – largest segments of time… • Eras – based on changes in life forms (based on mass extinction events) • Periods – existing life world wide. • Epochs ‐ Differences in life forms continent to continent. i Precambrian Time.. (4 5 bya 500 mya) (4.5 bya. – 500 mya) * Longest part of Earth’s history (apx. 4billion years). • Life (little to none) – simple, single‐celled organism. organism • ex) bacteria, algae, fungus. Paleozoic Era… ( 500 ( 500mya – 250 250 mya.) ) • Means Ancient Life : Age of Marine g Invertebrates. • Life Life – Marine (fish), amphibians(breath Marine (fish) amphibians(breath oxygen ), first reptiles, first land plants. • Geology ‐ Geology Pangaea formed, Many Volcanoes, Pangaea formed Many Volcanoes Appalachian Mountains. • End ‐mass extinction of land (70%) and d fl d( ) d marine animals (90%) . Sea level drop and climate change. li h Mesozoic Era (250 mya 65 mya.) (250 mya. – 65 mya ) • Means Middle Life: Age of Reptiles Means Middle Life: Age of Reptiles • Life ‐ if First flowers and birds. Dinosaurs i fl d bi d i evolved and dominated. • Geology – Pangaea breaks up. • End – Dinosaur mass extinction (asteroid impact). Cenozoic Era (65 mya. – today) • Cenozoic Cenozoic ‐ Means Recent Life: Age of Means Recent Life: Age of Mammals. • Life – Life Evolution of mammals. First humans Evolution of mammals First humans (homo sapiens). • Geology – G l A d Al Hi l Andes; Alps; Himalayas. Cooler C l climates (ice ages). • End – Still going on …. Difficulties with Compiling the Timescale • There is not a complete record of events in any one place. l • Much of the record is based on past life ( (fossil record). However, there are some cases ) , where this record is incomplete. • We need to rely on geologic “correlation” (matching) methods (matching) methods…. Methods of Rock Correlation…. Methods of Rock Correlation…. • Relative age dating laws….. Relative age dating laws • Using fossil records….. i f il d • Rock Correlation… • Walking the outcrop (simplest & most direct).