Review Geologic Time Plate Tectonics Crustal Deformation Global

Review Geologic Time Plate Tectonics Crustal Deformation Global Climate Change

Geologic Time

GEOL 131: Geologic Time: Relative Dating Principles of Relative Dating • • • Superposition Original Horizontality Lateral Continuity Cross-cutting Relationships Inclusions

GEOL 131: Geologic Time: Relative Dating Unconformities: Three types Disconformity Separates two horizontal layers Angular unconformity Separates horizontal from tilted layers Nonconformity Separates sedimentary from non-sedimentary

GEOL 131: Geologic Time: Fossils Ranges and Age Bracketing • Overlapping fossil ranges can be used to “bracket” the age of a rock layer

GEOL 131: Geologic Time: Radiometric Dating Radioactivity • Spontaneous changes in atomic nuclei • Loss or gain of protons or neutrons • Occurs at known rates – Each element’s decay rate is different • Parent: The element that changes • Daughter: The product of the change – A different element – A different version (isotope)of the parent element • Half-life: Time required for one-half of remaining parent atoms to decay

GEOL 131: Geologic Time: Radiometric Dating Example Granite contains mineral with trace amount of uranium. Measurements show the sample contains 25% parent (U-235) and 75% daughter (Pb-208). The halflife of U-235 is 704 million years. How old is the granite? Could we determine the age if the rock were sedimentary or metamorphic?

GEOL 131: Geologic Time: The Time Scale, structure PRESENT EARTH FORMS

Plate Tectonics

GEOL 131: Plate Tectonics: Continental Drift • Alfred Wegener • Pangea: “All lands” • 200 million years ago

GEOL 131: Plate Tectonics: Continental Drift • • The “continental jigsaw puzzle” Trans-oceanic fossil matching Trans-oceanic rock matching Ancient climates

GEOL 131: Plate Tectonics Overview Earth’s Layers • Based on seismic wave behavior – Lithosphere, asthenosphere, mesosphere, outer core, inner core

GEOL 131: Plate Tectonics: Divergent Boundaries

GEOL 131: Plate Tectonics: Convergent Boundaries Convergent boundaries

GEOL 131: Plate Tectonics: Transform Boundaries Transform boundaries

GEOL 131: Plate Tectonics: Testing the Plate Tectonic Theory Ocean Drilling • Sediment thickness and crustal age increase away from oceanic ridges

GEOL 131: Plate Tectonics: Testing the Plate Tectonic Theory Hot Spot Tracks

GEOL 131: Plate Tectonics: Testing the Plate Tectonic Theory Paleomagnetism • Oceanic crustal rocks record the polarity in effect at the time they formed • Earth’s magnetic field has reversed many times • Normal polarity: North magnetic pole near north geographic pole • Reversed polarity: N. magnetic near S. geographic • Symmetrical “stripe” pattern of normal and reversed polarity created in ocean crust

Crustal Deformation

GEOL 131: Crustal Deformation • Deformation: change in shape or position as result of differential stress. • Elastic: Rock bends but snaps back to original shape • Brittle: Rock breaks • Ductile: Rock bends permanently

GEOL 131: Crustal Deformation: Folds Anticlines & Synclines

GEOL 131: Crustal Deformation: Folds Domes & Basins

GEOL 131: Crustal Deformation: Folds Monoclines

GEOL 131: Crustal Deformation: Folds Fold Orientations • Symmetrical – Both limbs have same dip angle • Asymmetrical – Limbs have different dip angles • Overturned – One limb tilted more than 90 degrees • Recumbent – Both limbs horizontal

GEOL 131: Crustal Deformation: Folds Recognizing folds in map view Oldest layer Youngest layer

GEOL 131: Crustal Deformation: Faults & Joints Dip-Slip Faults • Normal faults – Tensional stress – Hanging wall moves down • Reverse faults – Compressional stress – Hanging wall moves up • Thrust faults – Compressional stress – Hanging wall moves up – Lower angle than reverse faults

GEOL 131: Crustal Deformation: Faults & Joints Strike-Slip Faults • Movement is horizontal, caused by shear stress

GEOL 131: Crustal Deformation: Faults & Joints • Fractures with no movement • Cause accelerated weathering Weathered joints in southern Utah

Types of Mountain Building • Fault-block: Formed by displacement of rock along fault (normal) • Andean: Formed by subduction of oceanic crust beneath continent • Collisional – Cordilleran: Collision and joining together (accretion) of small fragments and islands to a continental margin – Alpine: Two continental masses collide and are welded together. Formed by the closure of major ocean basins

Global Climate Change

GEOL 131: Global Climate Change: Some Atmospheric Basics Major Components • Don’t vary significantly

GEOL 131: Global Climate Change: Some Atmospheric Basics Variable Components • Vary by location and over time • Three important ones: – Water vapor • Clouds, precipitation • Greenhouse gas (traps heat) • State changes absorb or release energy – Aerosols • Suspended solid or liquid particles • Dust, pollen, liquid water, bacteria, etc. – Ozone • Absorbs UV radiation • Concentrated in “ozone layer” (about 15 miles up)

GEOL 131: Global Climate Change: Some Atmospheric Basics Structure of the Atmosphere • Troposphere – Bottom layer – Temperature decreases with altitude – Thickness varies – average height is 12 km • Stratosphere – About 12– 50 km – Temperature increases at top • Mesosphere – About 50– 80 km – Temperature decreases • Thermosphere – No well-defined upper limit – Fraction of atmosphere’s mass – Gases moving at high speeds

GEOL 131: Global Climate Change: Heating the Atmosphere Paths of Solar Radiation • Reflection: – Light bounces back from an object at the same angle and intensity that it hits the object – Albedo: portion of the total radiation that is reflected (depends on surface) • Scattering: – Sends light out in different directions (why the sky is blue) • Absorption: – Converts energy to heat – Gases absorb some wavelengths more strongly that others • N 2: poor absorber • O 2 and O 3: good absorbers • H 2 O: good absorber

GEOL 131: Global Climate Change: Heating the Atmosphere Greenhouse Effect • Recall: – Sun emits shortwave radiation – Earth emits longwave radiation • The atmosphere is better at absorbing longwave radiation than shortwave. – Earth gets heated from the ground up

GEOL 131: Global Climate Change: Detecting Climate Change Evidence for past climate change • Paleoclimatology – reconstruct past climates • Instruments – limited records • Proxy data – natural climate recorders – Seafloor sediments – Oxygen isotopes – Glacial ice – Tree rings – Fossil pollen – Corals – Historical documents

GEOL 131: Global Climate Change: Natural Causes of Climate Change • Plate movements • Orbital variations • Volcanic Activity – Aerosols • Solar variability

GEOL 131: Global Climate Change: Human Impact on Global Climate Rising CO 2 • CO 2 is a greenhouse gas – Allows shortwave solar radiation to pass through to Earth, but slows long-wave Earth radiation from passing back into space • Global temperatures have increased in response to increased atmospheric CO 2

GEOL 131: Global Climate Change: Human Impact on Global Climate Trace gases and aerosols • Methane – Less abundant than CO 2, but more effective at absorbing outgoing radiation • Nitrous oxide – Greenhouse gas that lasts for 150 years in the atmosphere • Chlorofluorocarbons (CFCs) – Commercially produced chemical that depletes the ozone • Aerosols – Produce cooling effect by reflecting sunlight back to space

GEOL 131: Global Climate Change: Climate Feedback Mechanisms Types • Positive feedback: changes that reinforce the initial change • Negative feedback: produces results that are opposite of the initial change and tend to offset it

GEOL 131: Global Climate Change: Some Consequences of Global Warming Consequences • Sea level rise • Changing Arctic – Sea ice declining – Thawing of permafrost • Ocean acidification – Rising CO 2 in atmosphere impact chemistry of ocean

Exam 3 • Sections 01 and 02 – Tuesday, December 11, 1: 40 -3: 25 pm • Section 70 – Tuesday, December 11, 5: 30 -7: 15 pm • Bring – calculator – 3 x 5 inch notecard (front and back, handwritten) • You’ll be given: – Decay curve – Half-life table – Geologic time scale