Geology Exam 1

Depositional basin

Depositional basin

weakly sedimented rocks

Mountain ranges

Resistant metamorphic and igneous rocks

Isostasy

Equilibrium between parts of the Earth’s crust

Rises if material is removed, sinks if added

Hydrosphere

Atmosphere + ocean

Average continental elevation

0-1 km

Erosion is driven by _____________ processes

Exogenic

Exogenic processes

External processes imposed on landscapes

Wind, water, and ice

Climate driven

Endogenic processes

Internal processes - driven by tectonics and volcanism

raises mountains, elevates topography

Asthenosphere

ductile, slowly deforming layer in upper mantle

Quaternary

Current geological period

Long glacial periods, brief warm periods

Nested landforms

Younger landforms are contained within older landforms in depositional environments

Water eroded landforms

younger sediment is deposited further down

Older surfaces more elevated than younger - opposite of superposition

Weathering rinds

Weathering attacks near the surface

thicker rinds indicate slower weathering rate

Rate decreases as degree of weathering increases

Thresholds

Physical or chemical conditions that trigger a change in state or shift to new average conditions when reached or exceeded

James Hutton concluded most present land surface formed…

At the bottom of the ocean

Remote sensing includes

Satellite radar

Airborne LiDAR

Aerial photography

GPS is __________ remote sensing

Passive

LiDAR

Airborne pulsed laser scanning system

2.5 rendering of landscape (pixels)

First digital elevation model method

Digitizing paper contour maps

Active remote sensing example

Radar

Remote sensing

Gathers large amounts of information quickly over a wide area

requires computers and models

Active remote sensing

Sends out a pulse of energy, receives that energy back, and analyzes the characteristics of the energy pulse as it returns to the detector

SAR

Synthetically Aperture Radar

Active remote sensing

image is measured twice from the same point in orbit, measures topography over vast areas

Passive remote sensing

Uses a detector to measure the amount and wavelength of energy emitted from Earth’s surface

Lasers

Measure the range to a point or target based on travel time of the laser

Relative dating techniques

Landform degradation

Cross-cutting relationships

Degree of soil development

Carbon-14 production

Nitrogen is bombarded by cosmic radiation in the upper atmosphere

Potassium-argon dating

Dating method used to directly measure the age of volcanic rock

40K → 40Ar + 40Ca

Sample is split for two separate measurements

Absorbed atmospheric Argon causes age error

Useful for material older than 100,000 years

40 Ar → 39 Ar

Single measurement for 2 Ar isotopes

Accounts for excess argon

min age of 10,000 years

Uranium series dating

U-Pb

takes a long time, NOT applicable to quaternary

Intermediate daughters have shorter half-lives

Cosmogenic exposure dating

AGE OF EXPOSURE

Bombardment by cosmic rays can create specific isotopes in situ

Luminescence dating

AGE OF BURIAL

based on dose of ambient radioactive bombardment of a crystal grain

Thermochronometry

Timing of exumation

Amount of damage can be used to determine when crystals cooled

Estimates long term erosion over time scales of millions to 100s of millions of years

Lichenometry

Certain varieties of lichen have predictable, circular growth patterns

Relative dating technique

Sclerochronometry

A method using growth patterns to estimate age and study environmental changes

Amino Acid racemization

Useful for organic material

Right or left handed, reverse randomly

Living systems use RIGHT handed aa

Magnetic reversals

Fossil magnetic field can be preserved and measured in sedimentary/igneous rocks

low resolution for quaternary

Magnetic secular variations

Short-term variations in magnetic field direction can be effective for continuous sections of quaternary sediment

Denudation

Weathering and erosion

Weathering

sediment generation

Erosion

sediment removal

Radiocarbon dating half-life and max age

5730;8

Regolith

Unlithified and weathered material covering fresh bedrock

Exfoliation sheets

Form parallel to the earth’s surface

Which weathering type dominates cold climates?

Physical weathering (freeze thaw)

Oxidation

chemical weathering process that changes the ionic state of a metal cation

How does a working hypothesis differ from a ruling theory?

Working hypothesis is a means of determining facts

Hydrolysis

Weathering process that produces clay minerals

Inselbergs

landforms that develop as residual landforms in areas with deep weathering zones

Smectite

group of clay minerals with the largest gap between sheets, absorbing more water

Quartz

Very stable mineral

Soluble conditions for Calcium carbonate

Acidic and neutral pH

Beta decay

Used in radiocarbon dating

Neutron replaces a proton

Accelerator mass spectromerty

Measures amount of Carbon-14

Errors with radiocarbon

Half-life was originally incorrect

Nuclear bomb testing makes material appear younger

Beta emission

Atom captures a neutron, loses a proton