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LECTURE 1 - Introduction Hrvoje Tkalčić *** N.B. The material presented in these lectures is from the principal textbooks, other books on similar subject, the research and lectures of my colleagues from various universities around the world, my own research, and finally, numerous web sites. I am grateful for some figures I used in this lecture to E. Garnero and L. Breger. I am thankful to many others who make their research and teaching material available online; sometimes even a single figure or an idea about how to present a subject is a valuable resource. Please note that this PowerPoint presentation is not a complete lecture; it is Units and scales Time… Time is a fundamental variable in geophysics. Geophysical images of Earth’s surface and interior are snapshots of Earth’s dynamic processes. Time How are relative ages of rocks classified? Fossils (remnants of prehistoric life succeed each other in systemic fashion) How are absolute ages of rocks determined? Radioactive isotope dating Time… -> Fossils This evolution is a clock of relative time, called the Principle of faunal succession. OLDEST one-celled organisms multi-celled organisms allows geologists to identify rocks of same age in different places. organisms with shells fishes plants insects amphibians reptiles YOUNGEST mammals Geologic Time Chart If the entire Earth’s history were scaled to 1 year… The appearance of planet Earth -around 4:15pm the first hominids appear in East Africa -between 8pm and 9pm, the first humans appear in Africa -at 8:04pm, humans make their first tools -around 8:30pm, they make their first shelters -between 9pm and 10pm, humans arrive to Europe Geologic time Atoms, minerals and rocks rock minerals mineral collection of one or more minerals A collection of one or more types of atoms Atoms, minerals and rocks Atomic structure Example: mineral quartz made up of silicon (Si) & oxygen (O) atoms 2- O 4+ Si 2- O 2- O 2- O Atoms, minerals and rocks Example: Granite & constituent minerals Rocks Sedimentary Igneous Metamorphic Average composition of the continental crust Percent of elements by WEIGHT Average composition of the continental crust Percent of elements by VOLUME Sedimentary rocks Grand Canyon Alps, Himalayas, etc. - consist of sedimentary rocks, laid down over many millions o But, in what sea were the Himalayan rocks deposited and how did they get sandwic between India and the Asian landmass? In the geology textbooks of the mid twentieth century - there were no satisfactory an Dynamic Earth: how did plate tectonics concept developed? 16th century observation of coastal fits Alfred Wegener 1912 observed mismatch of climate features Proposed “continental drift” Pangea = Laurasia + Gondwana Same fossils found on different continents Mid-Ocean ridges Earthquake distribution and focal mechanisms The Earth’s Interior CRUST Oceanic 0-6 km (“young”, < 180 m.y.) Continental 0-34 km (older, up to 3.8 b.y.) MANTLE Upper 34-670 km Lower 670-2900 km Brittle “lithosphere” Plastic flow “astenosphere” CORE Outer (liquid) 2900-5160 km Inner (solid) 5160-6370 km Maxwell’s equation and its implication for the geodynamo: T he force on a charge F is q (E B v ) T he law of electromagnet ic induct ion : E ds d dt B n da a Applying the Stokes theorem, E n da B n da a a t E B How do these terms remain in balance? t Sea floor spreading from the age of rocks and the magnetic “stripes” due to the magnetic field reversals “Conveyor belt” concept by H. Hess (1960) Continents with no “plow experience” Plate tectonics and boundaries Active Earth movie Continental and oceanic crust Collision may cause: •Faulting •Earthquakes •Mountain building •Volcanoes QuickTime™ and a Cinepak decompressor are needed to see this picture. Plate tectonics and boundaries Structural contrasts Tonga-Fiji islands arc with earthquakes occurring within the descending “slab”. Asthenosphere on both sides of the descending slab with convection, “drag” and secondary spreading. Andean volcanic arc with earthquakes at the slab-lithosphere Active Earth movie Plates slower than average faster than average Study of the deep Earth’s interior requires a multidisciplinary approach +Geodesy +Mathematical geophysics +Geomagnetism +Geochemistry +Geology +Computer science