Earth Systems and Earth Systems and ResourcesResources

Earth Science ConceptsEarth Science Concepts

Earth Science ConceptsEarth Science Concepts

• Geologic Time Scale

• Plate Tectonics

• Earthquakes

• Volcanism

• Seasons

• Solar intensity and Latitude

Geologic Time ScaleGeologic Time Scale

• The geologic time scale is a system of chronological measurement that relates stratigraphy to time

• Used by geologists, paleontologists, and other earth scientists to describe the timing and relationships between events that have occurred throughout Earth’s history.

Figure 11.10

• The clock representation shows some of the major units of geological time and definitive events of Earth history. The Hadean eon represents the time before fossil record of life on Earth.

• Other subdivisions reflect the evolution of life; the Archean and Proterozoic are both eons, the Paleozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon.

• The two million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale.

EonsEons• An eon is the largest interval into which

geologic time is divided. Four eons are:– Hadean Eon - oldest

• Some of the samples brought back from the moon were formed during the Hadean Eon.

– Archean Eon follows the Hadean. • Archean rocks are the oldest rocks we know of

on the Earth.

– Proterozoic Eon follows the Archean.– Phanerozoic Eon is the most recent of the

four eons.

Eras Eras

• Each of the eons is subdivided into shorter time units called eras.

• The Phanerozoic Eon is divided into:– Paleozoic (old life) Era.– Mesozoic (middle life) Era.– Cenozoic (recent life) Era.

Paleozoic Era, early land plants appeared, expanded and evolved.

Paleozoic Era – Rapid blooming of life: marine invertebrates, fishes, amphibians, and reptiles.

The The Mesozoic EraMesozoic Era saw the rise of the dinosaurs, which saw the rise of the dinosaurs, which became the dominant vertebrates on land. Mammals first became the dominant vertebrates on land. Mammals first

appeared during the Mesozoic Era, as did flowering plants.appeared during the Mesozoic Era, as did flowering plants.

Mammals dominated theMammals dominated the Cenozoic EraCenozoic Era. Grasses evolved . Grasses evolved during the Cenozoic Era, becoming an important food for during the Cenozoic Era, becoming an important food for

grazing mammals.grazing mammals.

PeriodsPeriods

• The Eras of the Phanerozoic Eon are divided into periods.– Periods defined on the basis of the fossils

contained in the equivalent rocks.– Two recent divisions are the Quaternary

Period and Tertiary Period

EpochsEpochs• Periods - subdivided into epochs - based on

the fossil record• Tertiary Period divided into 5 epochs:

– Pliocene– Miocene– Oligocene– Eocene– Paleocene

• Quaternary Period divided into 2 epochs:– Holocene– Pleistocene

Relative AgeRelative Age

• Placing geologic events in a chronological order as determined from their position

• When discussing relative age, one rock is simply older or younger than another

Absolute AgeAbsolute Age

• Using various methods of producing an actual age of a rock unit expressed in years.

• Most useful and widely used method of determining absolute age is radiometric dating. (aka radioactive decay)

Half-LifeHalf-Life

• The amount of time required for one-half of the original parent radioactive isotope to decay to its stable daughter isotope

• The amount of parent isotope will never reach zero.

(This means if we graph the ratio of parent to daughter changes with age, we will obtain a decay curve, which approaches, but never intersects the horizontal axis.)

Radioactivity and TimeRadioactivity and Time

Plate TectonicsPlate Tectonics

• Plate tectonics - scientific theory that describes the large-scale motions of Earth's lithosphere– continental drift - developed during the first

decades of the 20th century – seafloor spreading - developed in the late

1950s and early 1960s

Plate TectonicsPlate Tectonics

Because the continentsare merely “passengers”on the larger plates –we no longer refer to “continental drift” butnow call the processplate tectonics*.

*from the Greek “tektonicos” for building or construction

Fossil EvidenceFossil Evidence

Sea-Floor SpreadingSea-Floor Spreading

Harry Hess’s idea of how the mountain ranges formed on the ocean floor – however, he had no proof that this actually happened (1950’s).

Mid-Ocean RidgesMid-Ocean Ridges

World’s largest mountain ranges are found under the oceans

Oceanic Mountain RidgesOceanic Mountain Ridges

Mid-Ocean Ridge MapMid-Ocean Ridge Map

Plate MovementPlate Movement

• Tectonic plates move because the Earth's lithosphere has a higher strength and lower density than the underlying asthenosphere.

• Density variations in the mantle result in convection.

Major PlatesMajor Plates

Plate Boundary ActivityPlate Boundary Activity

LithosphereLithosphereBroken up into tectonic plates

- 7 or 8 major plates and many minor ones Where plates meet, relative motion determines the type of boundary:

- convergent - divergent - transform

Earthquakes, volcanoes, mountain-building, and ocean trenches occur along plate boundaries. Lateral relative movement of the plates typically varies from zero to 100 mm annually.

Types of Plate BoundariesTypes of Plate Boundaries

Plate margins: divergent (where two plates move apart from each other); convergent (where two plates collide); and transform (where two plates slide past each other)

Tectonic PlatesTectonic Plates

• Types: oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust

• Along convergent boundaries - – Subduction carries plates into the mantle; the material

lost = the formation of new (oceanic) crust along divergent margins by seafloor spreading

– Total surface of the globe remains the same– Also referred to as the conveyor belt principle

Plate BoundariesPlate Boundaries

Where the plates join, most of the world’s volcanoes, earthquakes, and major mountain belts occur.

Ocean-Continent ConvergentOcean-Continent ConvergentWhen an oceanic plate collides with a continent, it will always be the oceanic plate that subducts. Features are similar to those of ocean-ocean margins. Volcanic arcs caused by ocean-continent convergent margins include the Cascades (the mountain range containing Mount Saint Helens) and the Andes.

Formation of HimalayasFormation of Himalayas

Continent-Continent DivergentContinent-Continent Divergent

Where continental plates split apart, acontinent-continent divergent margin or continental rift forms. Normalfaulting because of the tensional stress will develop down-dropped riftvalleys and thinner crust. Because of the thin crust, there is usually a high geothermal gradient as evidencedby hot springs and volcanic activity.

Active continent-continent divergent marginsinclude the East African Rift, the Red

Sea and the Rio Grande Rift.

Active Continental RiftingActive Continental Rifting

Active Continental RiftingActive Continental Rifting

Rio Grande Rift(New Mexico)

East African Rift

Transform MarginsTransform Margins

Transform margins may also occur along continental margins, such as the SanAndreas fault. The San Andreas fault is a transform margin joining the divergentmargin in the Gulf of California to the convergent margin of the Cascades. To the east of the San Andreas is the North American Plate; to the west, the Pacific Plate.

Triple JunctionTriple Junction• Triple junction - place where 3 tectonic plates

meet• Roughly 50 plates on Earth with about 100 triple

junctions among them• At any boundary they are either:

– spreading apart (making mid-ocean ridges at spreading centers),

– pushing together (making deep-sea trenches at subduction zones), or

– sliding sideways (making transform faults)• A meeting of three plates - also a meeting of

three boundaries, each with its own motion

EARSEARS

The East African Rift System (EARS) is one the geologic wonders of the world, a place where the earth's tectonic forces are presently trying to create new plates by splitting apart old ones.

EARSEARS

Triple

Junction

Natural Geologic HazardsNatural Geologic Hazards

• Earthquakes

• Volcanic Eruptions

EarthquakesEarthquakes

When the Earth quakes, energy stored in elastically strained rocks is suddenly released.

More energy released = stronger quakeMassive bodies of rock slip along fault

surfaces deep underground.Earthquakes - key indicators of plate

motion

““Parts” of an earthquakeParts” of an earthquake

- focus - the point where earthquake starts to release the elastic strain of surrounding rock- epicenter - the point on Earth’s surface that lies vertically above the focus of an earthquake- rupture front – the place where fault slippage begins at the focus and spreads across a fault surface (The rupture front travels at roughly 3 kilometers per second for earthquakes in the crust)

Earthquake “parts”Earthquake “parts”

Focus

Epicenter

Rupture front

Primary EffectsPrimary Effects

• Shaking

• Permanent displacement of ground

Not Designed to Withstand an Not Designed to Withstand an EarthquakeEarthquake

Collapse of city buildings – Armenia - December 7, 1988.

Shaking Causes LiquefactionShaking Causes Liquefaction

Destruction of part of Anchorage, Alaska, caused liquefactionas a result of the earthquake of 1964.

California earthquake 1989

California earthquake 1989

Ground DisplacementGround Displacement

Secondary EffectsSecondary Effects

• Rockslides

• Urban fires

• Flooding caused by subsidence

• Tsunamis

RockslideRockslide

Fire caused by broken gas linesFire caused by broken gas lines

A result of the Loma Prieta earthquake in 1989 – San Francisco

FloodingFlooding

TsunamiTsunami

VolcanismVolcanism

• An active volcano occurs where magma (molten rock) reaches the earths surface through a central vent or a long crack (fissure).

• Volcanic activity can release ejecta (debris ranging from large chunks of lava rock to ash) liquid lava, and gases into the environment.

Volcanic HazardsVolcanic Hazards

• Low viscosity may result in lava fountains; and fast flowing lava

• Falling lava bits may spatter• Bombs may be ejected over great distances• Volcanic ash may extend over large areas• Mudflow chances are increased

Slow-moving - High ViscositySlow-moving - High Viscosity

The way lava flows is controlled by viscosity – Hawaii 1989

Fast-Flowing LavaFast-Flowing Lava

Low-viscosity lava – initial temp 11000C – Hawaii 1983

Lava FountainsLava Fountains

Mauna Ulu – A vent on the flank of Kilauea Volcano, Hawaii, starts with a spectacular fountain as gases are released from the rising magma.

(Use of a telephoto lens foreshortens the field of view. The observer is several hundred meters away from the fountain which reached as highas 300 meters.)

Eruption Eruption Column Column of Hot of Hot

Gas and Gas and Fine Fine

TephraTephra

Mount St. Helensduring the eruptionevent of May 1980.

A house is no match for lava….A house is no match for lava….

An advancing tongue of very fluid basaltic lava setting fire to a house in Kalapana, Hawaii, during an eruption of Kilauea Volcano in June 1989. Flames at the edge of the flow are burning the lawn.

Ring of FireRing of Fire

Beneficial volcanoes…..Beneficial volcanoes…..

• Outstanding scenery– Mountains– Lakes

• Soil– Fertile soil produced by weathering of lava

Mt. McKinley, AlaskaMt. McKinley, Alaska

Mt. Fuji, JapanMt. Fuji, Japan

Crater LakeCrater Lake

Crater Lake, OregonCrater Lake, Oregon

Hot SpotHot Spot

• Some volcanoes result from “hot spots”

• Hot spot – an area where magma from deep within the mantle melts through the crust

• Hot spots – often lie in the middle of continental or oceanic plates, far from any plate boundaries

Hot SpotsHot Spots

Hawaiian Islands formed one by one overmillions of years as the Pacific plate driftedover a hot spot.

Lab AssignmentLab Assignment

• Plate Tectonics - Investigation # 2

(page 27 – 34)

• Materials: – Lab Manual– World map with latitude and longitude – Colored pencils– Internet site http://neic/usgs.gov/neis/

SeasonsSeasons

• A season is a subdivision of the year marked by changes in weather, ecology, and hours of daylight.

• Result from the yearly revolution of Earth around Sun and

• Tilt of Earth’s axis relative to the plane of revolution

SeasonsSeasons

Solar Intensity & LatitudeSolar Intensity & Latitude

• Yearly changes in the position of the Earth's axis cause the location of the sun to wander 47° across our skies.

• Changes in location of sun have direct effect on intensity of solar radiation

• The intensity of solar radiation is largely a function of the angle of incidence, the angle at which the sun's rays strike the Earth's surface.

Positions of SunPositions of Sun

• Directly overhead (90° from the horizon) incoming insolation strikes surface of Earth at right angles - most intense.

• Sun @ 45° above horizon, incoming insolation strikes Earth's surface at an angle. (This causes the rays to be spread out over a larger surface area reducing the intensity of the radiation)

Sun Angle of IncidenceSun Angle of Incidence

This figure models the effect of changing the angle of incidence from 90 to 45°. As illustrated, the lower sun angle (45°) causes the radiation to be received over a much larger surface area. This surface area is approximately 40% greater than the area covered by an angle of 90°. The lower angle also reduces the intensity of the incoming rays by 30%.

Seasons………..Seasons………..

• Changes in position of Earth's axis relative to the plane of the ecliptic also cause seasonal variations in day length to all locations outside of the equator.

• Longest days - summer solstice north of the equator and winter solstice for Southern Hemisphere.

• The equator experiences equal day and night on every day of the year.

• Day and night is also of equal length for all Earth locations on the autumnal and vernal equinoxes

This figure describes the change in the length of day for locations at the equator, 30, 50, 60, and 70° North over a one-year period. This suggests that days are longer than nights in the Northern Hemisphere from March equinox to September equinox. Between September to March equinox days are shorter than nights in the Northern Hemisphere. The opposite is true for the Southern Hemisphere. The graph also shows that the seasonal variation in day length increases with increasing latitude.

This figure shows the potential This figure shows the potential insolation available for equator and insolation available for equator and locations in the Northern Hemisphere locations in the Northern Hemisphere over a one-year period. Locations at over a one-year period. Locations at the equator show the least amount of the equator show the least amount of variation in insolation over a one-year variation in insolation over a one-year period. These slight changes in period. These slight changes in insolation result only from the annual insolation result only from the annual changes in the altitude of the sun changes in the altitude of the sun above the horizon, as the duration of above the horizon, as the duration of daylight at the equator is always 12 daylight at the equator is always 12 hours. The peaks in insolation intensity hours. The peaks in insolation intensity correspond to the two equinoxes when correspond to the two equinoxes when the sun is directly overhead. The two the sun is directly overhead. The two annual minimums of insolation occur annual minimums of insolation occur on the solstices when the maximum on the solstices when the maximum height of the sun above the horizon height of the sun above the horizon reaches an angle of 66.5°.reaches an angle of 66.5°.

The end…………….