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 most likely accompanied by an in-class presentation of main mathematical concepts (on transparencies or blackboard).***
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. allows geologists to identify rocks of same age in different places. OLDEST YOUNGEST one-celled organisms multi-celled organisms organisms with shells fishes plants insects amphibians reptiles 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 O 2- O 2- Si 4+ O 2- O 2-
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 of years But, in what sea were the Himalayan rocks deposited and how did they get sandwiched between India and the Asian landmass? In the geology textbooks of the mid twentieth century - there were no satisfactory answers.
Dynamic Earth: how did plate tectonics concept developed? 16 th century observation of coastal fits Same fossils found on different continents R E J E C T E D! Alfred Wegener 1912 - observed mismatch of climate features Proposed continental drift Pangea = Laurasia + Gondwana
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: The force on a charge is r F = q " ( r E + r B # r v ) The law of electromagnetic induction : r $ E " d r s = % d dt r $ B " n r da r Applying the Stokes theorem, & # E r " n r ( ' r + $ da = % $ * B -" n r da ) a 't, a. & r # E r = % ' r B How do these terms remain in balance? 't a 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
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 slablithosphere boundary - thick lithosphere prevents secondary spreading. 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