L2 - Geological Time PDF

Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life Dr Adrienne Brotodewo Pages 368-387, 394-422 and Figures taken from Earth Science (2015) 14th Ed, Tarbuck, Lutgens and Tasa, Pearson Education Astronomy an...

Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life Dr Adrienne Brotodewo Pages 368-387, 394-422 and Figures taken from Earth Science (2015) 14th Ed, Tarbuck, Lutgens and Tasa, Pearson Education Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Lecture 2 Geological Time and Evolution of Life History of Geologic Time Relative Dating Fossils Radioactivity and Radiometric Dating Geologic Time Scale Evolution of Life 2 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) History of Geological Time Catastrophism During the mid 1600s, James Ussher concluded Earth was only a few thousand years old Landscape developed by catastrophes – short time periods Modern geology Uniformitarianism James Hutton, Theory of Earth, late 1700s Fundamental principle of geology “the present is the key to the past” 3 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time Scale Difficulties in dating the time scale Not all rocks are datable (sedimentary ages are rarely reliable) Materials are often used to bracket events and arrive at ages 4 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Relative Dating Placing rocks and events in sequence - stratigraphy Law of superposition – oldest rocks are on the bottom Three main Principles Original horizontality: sediment is deposited on top of each other (youngest on the top) Cross-cutting relationships Inclusions 5 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Relative Dating Principle of original horizontality – sediment is deposited horizontally (youngest on the top) 6 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Relative Dating Principle of cross-cutting relationships – younger feature cuts through an older feature 7 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Relative Dating Principal of inclusions – one rock contained within another (rock containing the inclusions is younger) 8 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Relative Dating Unconformities An unconformity is a break in the rock record Types of unconformities Angular unconformity – tilted rocks are overlain by flat-lying rocks Disconformity – strata on either side are parallel Nonconformity Metamorphic or igneous rocks below Younger sedimentary rocks above 9 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Relative Dating Unconformities 10 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Relative Dating 11 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Relative Dating Correlation Matching rocks of similar age/composition in different regions Often relies upon fossils 12 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Fossils Remains or traces of prehistoric life Types of fossils Petrified cavities and pores are filled with precipitated mineral matter Formed by replacement cell material is removed and replaced with mineral matter Mold shell or other structure is buried and then dissolved by underground water Cast hollow space of a mold is filled with mineral matter 13 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Fossils Types of fossils Carbonization organic matter becomes a thin residue of carbon Impression replica of the fossil’s surface preserved in fine-grained sediment Preservation in amber hardened resin of ancient trees surrounds an organism 14 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Fossils Trace Fossils Indirect evidence includes Tracks – animal footprints made in soft sediment that later turned into sedimentary rock Burrows – in sediment, wood or rock made by an animal Coprolites – fossil dung and stomach contents Gastroliths – stomach stones used to grind food by some extinct reptiles 15 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Fossils Conditions favouring preservation Rapid burial Possession of hard parts Fossils and correlation Principle of fossil succession Fossils succeed one another in a definite and determinable order, therefore any time period can be recognised by its fossil content (William Smith, 1700 to 1800) Index fossils Widespread geographically Existed for a short range of geologic time 16 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Radioactivity and Radiometric Dating Atomic structure reviewed Nucleus Protons – positively charged Neutrons Neutral charge Protons and electrons combined Orbiting the nucleus are electrons – negative electrical charges 17 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Radioactivity and Radiometric Dating Atomic structure reviewed Atomic number An element’s identifying number Number of protons in the atom’s nucleus Mass number Number of protons plus (added to) the number of neutrons in an atom’s nucleus Isotope Variant of the same parent atom Different number of neutrons and mass number 18 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Radioactivity and Radiometric Dating Radioactivity Spontaneous breaking apart (decay) of atomic nuclei Radioactive decay Parent – an unstable isotope Daughter products – isotopes formed from the decay of a parent 19 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Radioactivity and Radiometric Dating Radioactivity Radioactive decay Types of radioactive decay Alpha emission Beta emission Electron capture 20 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Radioactivity and Radiometric Dating Radiometric dating - A reliable method of calculating the age of rocks and minerals that contain radioactive isotopes. Rate of decay for many isotopes have been precisely measured and do not vary under physical conditions on earth. 21 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Radioactivity and Radiometric Dating Half-life – the time for one-half of the radioactive nuclei to decay Requires a closed system Cross-checks are used for accuracy Complex procedure Yields numerical dates 22 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Radioactivity and Radiometric Dating 23 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Radioactivity and Radiometric Dating Radiometric dating Sm/Nd 2600 1.10 2500 1.05 TDM Sr/Rb (Ma) 1.00 2400 87/86 Sr 0.95 2300 0.90 U/Pb 2200 0.85 2100 0.80 2000 0.75 1900 0.70 399 499 600 700 800 900 998 24 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Radioactivity and Radiometric Dating Carbon-14 dating Half-life of only 5730 years Used to date very recent events Produced in upper atmosphere Incorporated into carbon dioxide Absorbed by living matter Useful tool for anthropologists, archeologists, historians, and geologists who study very recent Earth history 25 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time Scale Divides geologic history into units Originally created using relative dates Subdivisions Eon Greatest expanse of time Era Subdivision of an eon Eras are subdivided into periods Periods are subdivided into epochs 26 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time Scale The Precambrian Divided into the Hadean, Archean and Proterozoic eons represents ~90% of Earth’s history Creation of stable continental crust Partial melting of the mantle formed volcanic island arcs and ocean plateaus These crustal fragments collided and accreted to form larger crustal provinces Larger crustal areas were assembled into larger blocks called cratons Cratons form the core of modern continents 27 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time Scale The Precambrian Supercontinents Large landmasses consist of all, or nearly all, existing continents Pangaea was the most recent but perhaps an even larger one, Rodinia, proceeded it 28 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time Scale The Phanerozoic 542 million years Divided into the Paleozoic, Mesozoic, and Cenozoic eras Dominated by continental collisions and rifting of supercontinents, i.e. Pangaea and Gondwana Several episodes of glaciation 29 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Global Cratons 30 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time - Life on Earth 31 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time - Life on Earth Hadean SO2 + CO2 gas and hot early atmosphere Similar to modern near volcanic environments 32 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time - Life on Earth Prokaryotes 3.8 Ga first known life single-celled bacteria no nucleus Cyanobacteria use solar energy to synthesize organic compounds thus producing food Fossil evidence of these bacteria: stromatolite 33 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time - Life on Earth Precambrian (3.8 to 0.5 Ga) Water vapor clouds condensed Rainwater formed ocean and river systems Oxygen released by photosynthesizing bacteria Levels increased, eventually atmospheric ozone developed Acidic outgassing accelerated the rock weathering rate Salinity of the oceans increased from inflow of weathered material Oceans accumulated carbon dioxide 34 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time - Life on Earth Life diversifies at 0.5 Ga 35 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time - Life on Earth Phanerozoic (542 Ma to Present) Paleozoic (542 to 251 Ma) Life formed hard parts, i.e. shells Early Paleozoic: invertebrate marine life Late Paleozoic diversified and moved to land Lobe-finned fish adapted to land to become the first amphibians 251 Ma mass extinction Permian glaciation Destroyed 70% of all vertebrate species on land and 90% all marine organisms 36 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time - Life on Earth Phanerozoic (542 Ma to Present) Mesozoic (251 to 65.5 Ma) Dominant trees were gymnosperms Cycad, conifer, ginkgo Dinosaurs (reptiles) were dominant animals 65.5 Ma mass extinction (K-T boundary) Meteorite hits Yucatán Peninsula 37 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time - Life on Earth Phanerozoic (542 Ma to Present) Cenozoic (65.5 Ma to now) Mammals replace reptiles as the dominant vertebrate life on land Two groups evolved Marsupials and placentals Mammals groups became very large “Age of Flowering Plants” Flowering plants (angiosperms) strongly influenced the evolution of both birds and herbivorous mammals throughout the Cenozoic 2.6 Ma large mammal extinction: Ice Age ends 38 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time - Life on Earth Phanerozoic (542 Ma to Present) Cenozoic (65.5 Ma to now) Rise of Humans 4.2 million years ago (Ma): Australopithecus afarensis in Kenya 2.4 Ma: Early hominids – Homo habilis in Tanzania 2 Ma: Homo erectus originates in Kenya 1 Ma: Homo erectus invents the handaxe 0.2 Ma: Homo sapiens originated in Africa 39 Astronomy and the Universe (PHYS 1015) Lecture 2: Geological Time and Evolution of Life (Pages 368-387, 394-422) Geological Time - Life on Earth Phanerozoic (542 Ma to Present) Cenozoic (65.5 Ma to now) Rise of Humans 40,000 BCE: Early Australians arrive Population at 10,000 BCE estimated as 300,000 Ice Age: 30,000 to 12,000 BCE 28 000 BCE: Homo neanderthalis extinct 3,000 BCE: Egyptian, Indus Valley, Sumerian rise 1,000 BCE: Greek civilisation 1,788 CE: English convict ships land in Australia 40