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University of Toronto Mississauga
Jessica Hawthorn

Readings Pg.1-8 The Origin of Life On Earth How Geology Works  Geology is the study of the Earth  Fossils often provide insight into Earth‟s environmental changes whether or not they survived those changes How Paleontology Works  Paleontology is the science of studying fossils  It aims to understand fossils as once living organisms, living, breathing and dying in a real environment on a real but past Earth that we can no longer, smell or touch directly  Fossils will tell us about ourselves and background  An alert reader should be able to recognize four levels of paleontological interpretation 1. Inevitable conclusions, no possible alternatives 2. Likely interpretations –there may be alternatives 3. Speculations –they may be right, but there is not much real evidence one way or another 4. Guesses –they may be biologically more plausible than other guesses one might make, but for one reason or another they are untestable and must therefore be classified as nonscientific Planets in Our Solar System  Once a planet cools, conditions on its surface are largely controlled by its distance from the Sun and by any volcanic gases that erupt into its atmosphere from its interior –from this point onward, the geology of a planet greatly affects the changes that life might evolve on it  Mercury and the moon are airless and lifeless Bio211 Tuesday. September. 10 , 2013 Lecture 1 Origin of the Solar System - age of the universe: Big Bang – 15 billion years ago - planets formed near time of sun‟s formation - 4.6 billion years ago – age of the Earth - inner planets are rocky (mercury, venus, earth and mars) Origin of the moon - Moon formed from impact of protoplanet with Earth - Proportions of iron (Fe) and magnesium (Mg) differ from Earth‟s mantle Origin of Earth - Earth materials differentiated into four primary layers (and a few others) - Densest at center - Less dense materials rose to surface, cooled to form crust - Meteorite impacts increased concentrations of some elements in upper Earth Earth’s Structure - Inner Core: solid, 6370-5150 km deep - Outer core: molten, 5150-2890 km deep –mostly iron - Mantle: 2890-40 km deep - Comprises most of Earth‟s volume - Rocky, less dense than core - The uppermost portion is part of the lithosphere –behaves elastically - The mid-upper portion below lithospheric part, is the asthenosphere viscous, low density, behaves plastically - Moho: short for mohorovicic - the crust/mantle boundary; occurs within the lithosphere - Crust: 40-0km deep - Continental: thicker, less dense (under our feet) - Oceanic: thinner, more dense - Together with the uppermost mantle, makes up lithosphere Earth’s Lithosphere - Crust = upper lithosphere - Oceanic (mafic: rich in magnesium and iron, more dense) - Continental (felsic: rich in silicate minerals, less dense) - Lithosphere divided up into plates; some plates include continents Origin of continents - Earliest crust was made u of relatively dense oceanic basalts (fine-grained volcanic rocks) - Felsics (rocks rich in silicate minerals) differentiated to form nuclei of continental crusts - Modern analogue: Iceland Origin of Continents  Continental Accretion: deep marine sediments also accreted to continent, forming wedges between continental masses Earth is an Archive - geological record achieves Earth‟s history - Results from the interaction of complex systems within the planet - The lithosphere (specifically the sedimentary rocks of the crust) contains the record of life on Earth Reading 2 Pg. 71-73 Global Tectonics and Global Diversity  Earth‟s crust is made up of great rigid plate that move about under the influence of the convection of the Earth‟s hot interior  As they move, the plates affect one another along their edges, with results that alter the geography of the Earth‟s surface  Plate tectonic movements affect the geography of continents and oceans, which can in turn affect food supply, climate and the diversity of life  The more the continents are fragmented into smaller units, the more oceanic the world‟s climate becomes, and the more diverse its total biota.  Overall pattern of diversity data through time does receive a first-order explanation from plate-tectonic effects. However, this cannot be the reason for several reasons: 1. Changing faunas through time: If plate tectonics were the only control on diversity, much the same groups of animals should rise and fall with the changes in global geography. Instead, we see dramatic changes in different animal groups that succeed one another in time. 2. Increase in global diversity: The overall increase in global diversity from Ediacaran to Recent times is not predicted on plate tectonic grounds 3. Mass extinctions: Major extinctions are much more dramatic than major radiations. For example, the Permian extinction did not occur gradually over the 150 m.y of the later Paleozoic, as the continents collided and assembled piece by piece. Most likely, the continental assembly set up the world for extinction, then an “extinction trigger” was pulled. There are too many sudden “mass extinctions” in the fossil record for a plate tectonic argument to be completely satisfactory. Even if plate tectonic factors set the world up for an extinction, we seem to need some separate theory to explain the extinctions themselves. Changing Faunas Through Time –Three Great Faunas  Cambrian Fauna, Paleozoic Fauna, and the Modern Fauna  Faunas overlap in time, and the names are only for convenience  Cambrian Fauna –contains the groups of organism, particularly trilobites that were largely responsible for the Cambrian increase in diversity –but later declined in diversity in the Ordovician and afterward, even though other marine groups increased at that time.  Paleozoic Fauna –the success of it was almost entirely responsible for the great rise in diversity in the Ordovician, and declined afterward –suffered from the Late Permian extinction –lived in more tightly defined communities, with a more complex ecological structure Readings Deep Time Pg. 19-20  Two different ways to find the age of rocks: absolute, and relative dating  Age dating rocks can only work if one identifies components of the rocks that change with time or are in some way characteristic of the time at which the rocks formed  Absolute geological ages can be determined because newly formed mineral crystals sometimes contain unstable, radioactive, atoms.  Radioactive isotopes break down at a rate that no known physical or chemical agent can alter, and as they do so they may change into other elements  Paleontologists more often deal with a relative time scale, in which one says Fossil A is older than Fossil B, without specifying the age in absolute years  Geological Time Scale: the time scale is divided into a hierarchy of units for easy reference, with the divisions between major units often corresponding to important changes in life on Earth. –the names of the eras and periods are often unfamiliar and have bizarre historical roots Lecture 2 Thursday. September. 12 , 2013 Earth’s Lithosphere • Upper lithosphere = crust
 – Oceanic: more dense, rich in magnesium and iron (mafic) – Continental: less dense, rich in silica (felsic) • Lower lithosphere = uppermost part of mantle • Mohorovi i discontinuity (Moho) boundary between crust and 
 mantle, occurs within the lithosphere • Lithosphere divided into plates, sits on top of asthenosphere (part of the mantle) Plate Tectonics • Tectonics: movement of Earth‟s crust and large- scale rock deformation • Plate tectonics: movement of discrete segments of the lithosphere in relation to one another • Movement of plates (varying sizes) driven by convection •Plates form at spreading centres, destroyed at trench
s Deformation of rocks • Rocks can bend and flow under stress
 – Metamorphosis at high pressures and temperatures –  Folds and faulting  • Folds and faulting – Increase folding -> overturned fold -> overturned fold can break = fault Types of Faults  Faults: where rocks break and move on a large scale  Normal faults: extensional motion  Thrust faults: compressive motion  Strike slip faults: transform motion, also called transform faults e.g. San Andreas fault – parallel direction ^v Continental Drift  Early scientists recognized relationship between fossils on continents separated by sea  Most proposed a former connection via land bridges  Observation that continents fit together goes back as far as1858 (Antonio Snider- Pellegrini), though not popular then  Development of the idea that continents move across Earth‟s surface:  – Alfred Wegener (1910s)
 – Alexander du Toit (1920s and 1930s) o Alfred Wegener (1910‟s) o Wegner‟s Evidence – continents fit together, floral and faunal (plant and animal life) similarities, geological similarities o Biostratigraphy: correlation between fossils  Glaciation: orientation of glacial striations and till deposits on southern continents suggested they were linked. • Till: poorly sorted material that was entrained in the glacier and is deposited on the margins as the glacier melts • No sound mechanism provided • Wegener‟s possibilities: • Centrifugal force caused by 
 Earth‟s rotation? • Precession of the Earth (wobbling of axis)? • „Tidal argument' based on the tidal attraction of sun and moon? The Rise of The Tectonic Theory  Recognition of Mid-Atlantic Ridge as site of rupture and formation of oceanic crust in Atlantic – First inferred in 1850 – Actually discovered in 1872
 – First mapped in 1950s • Harry Hammond Hess (1960s)
 – “Geopoetry”: seafloor spreading; continents don‟t plow through/across seafloor
 – Crust must be created and destroyed – Driven by convection cells • Convection: – Rotational flow of fluid resulting from density imbalance – Material heated deep in the asthenosphere rises displaces cooler, denser material nearer surface • Palaeomagnetism: magnetization of rocks resulting from Earth‟s magnetic field at the time of their formation • Declination:anglethata compass needle makes with the line running to the geographic north pole  A palaeomagnetic test of plate tectonics: – Vine and Matthews (1963) measured magnetization of rocks across Indian Ocean central ridge – Found normal and reversed “stripes” creating a mirror image • Ridges: – Sites of crustal 
 formation – Hot rising mantle material rises to top of lithosphere, cools – Oceanic crust bends away from center to form ridge • Crust is destroyed at subduction zones Plate motion • Why plates move: – Convection cells in asthenosphere create drag on plate – Elevation at ridge pushes plate away
 – Plates pulled down by preceding subducted areas – Not all plates move at the same rate – • Can be measured using fixed points, such as hot spots – Hot spot: small stationary area where a thermal plume rises from the mantle • Hawaiian hot spot – Thermal plume creates 
 volcano – Plate moves away from plume – Stranded volcanoes cool, leaving an island chain • Global Positioning Systems (GPS) can also measure plate motion: – Earth-orbiting satellites identify motion and transmit back to ground-based receivers – Passive margins: tectonically inactive areas that accumulate sediment – Active margins: zones of tectonic deformation and igneous activity Divergent Plate Boundaries  Plates diverge at spreading zones – Mid-ocean ridges (MORs) – Rift valleys  Rifting  Can result in:  – Grabens: rift valleys bounded by normal faults; central block slips downward  – Mid-ocean ridges (MORs) Rifting • Examples: – Red Sea • Three-armed rift; one arm may die out – Mid-Atlantic Ridge Transform Plate Boundaries • Transform faults: – Enormous strike-slip 
 faults – Seismically active – Often occur at offset continental rift zones or MORs Convergent plate boundaries • Subduction zones: one plate slips beneath another – Trenches – Seismic activity – Volcanism • Subduction – Descending slab undergoes dehydration and melting – Molten material is less dense, rises • Subduction – Descending slab undergoes dehydration and melting – Molten material is less dense, rises 
 – Ring of Fire: around Pacific • Subduction associated with:
 – Volcanoes (including island arcs)
 – Deep-focus earthquakes (> 300 km deep) – Forearc basins: zones of intensely deformed rocks between igneous/island arc and deep-sea trench • Terranes: geologically distinctive regions of lithosphere • Terranes can be accreted onto margins of continents • Orogenesis: process of mountain building • Orogeny: result of mountain building event - Continental collision – Continental crust cannot be subducted – Suturing: unification of two continents along a subduction zone th September. 17 , 2013 Lecture 3 The Rock Cycle & Principles of Stratigraphy Foundations of Geology Principle of Uniformitarianism – There are inviolable laws of nature that have not changed in the course of time – “The present is the key to the past” - First founding principle of geology  what we observe in the present happened in the earth‟s past  • Actualism:   – Application of modern processes to ancient systems  An opposing view:  catastrophism  – Popular until early 1800s Materials and Processes • Mineral  – Naturally occurring inorganic solid 
 element or compound, minerals make up rocks  – Particular chemical composition/range of compositions and characteristic internal structure  • Rock  – Interlocking or bonded grains of minerals  • Outcrop/Exposure – rock that is exposed, we don‟t see so many rocks because it‟s covered in soil or under the pavement Rock Units –they can be divided into different units of different scope • Group: named groups of formations (largest unit) –one or more formations, formations can be subdivided into members, and members can be subdivided into beds • Formation: named unit of rock with specific lithology formed in a particular way • Member: smaller named rock unit, part of a formation • Bed: distinctive layer in a formation or member Rock Cycle • Surface and subsurface processes link materials to form three rock types: – Igneous
 – Sedimentary – Metamorphic Igneous Rocks • Formed by cooling and hardening of molten material –molten material is coming from the mantle and is increasing into the crust – Composed of interlocking grains, each consisting of a particular mineral • Magma: molten rock below surface –cools slowly –intrusive igneous rocks • Lava: molten rock at surface –cools quickly Intrusions: – slow-cooling – e.g., plutons, sills, dikes • Lava: molten rock, extrudes from vents at surface • Tuff: rock from consolidation of loose volcanic debris –when you have a big volcanic eruption you have ash in the air, the ash falls down and it consolidates into tuff (not really lava, splatter of lava) - you got larger crystals when there‟s more time to cool Sedimentary Rocks • Sediments: material deposited on Earth‟s surface by water, ice, air, chemical, or organic means
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