earth: the model planet

8/3/2019 Earth: the Model Planet

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EarthEarth

The Model PlanetThe Model Planet



Physical PropertiesPhysical Properties

Diameter: 12,756 kmat the equator




T he bulging at the equator and flattening atT he poles is called OBLATENESS.

I t¶s due to the rotation of the planet.

Earth is the most sphericalof all the planets.




Volume: 1.1 trillion cubic kilometers (km 3)

Mass: 5.97 x 10 24 kilograms




Density: 5500 kg/m 3 or 5.5 g/cm 3

± We compare the density of materials

like rocks & metals to the densitystandard: WATER!

Water¶s density is 1.0 g/cm 3




Earth is acombination of rocksand metals.



H ow old is the Earth?H ow old is the Earth?

About 4.6 billion years.



H ow was the earth formed?H ow was the earth formed?

AccretionDifferentiationInterior StructureEvidence



A rotating cloud of gas & dust:

a nebula



Rotation causes the nebula to flatten



A star ignites in the center and atemperature gradient forms.



Solid chunks, called planetissimals,begin to condense close to the star.



Accretion Accretion

Planetissimals begin to formnear the sun.

Gravity attracts planetissimalsinto larger bodies. Planetsbegin to grow.



DifferentiationDifferentiation

As earth grows, its gravitygrows too

It pulls in other planetissimals,which impact its surface.



DifferentiationDifferentiation

The heat generated plus theheat generated by radioactivedecay causes the entire earthto melt .



DifferentiationDifferentiationWhen the earth is molten, heavyelements (iron, nickel) sink to theinterior.

The lighter materials rise to thesurface.

The medium density rocks ends up inthe middle.

Layers form: core, mantle, crust.



M olten Earth, heated by impacts & radioactivedecay.

Differentiated (layered)Earth after cooling.



Interior StructureInterior StructureInner Core -kept solid by immensepressureOuter Core - less pressure allows it to be aliquidMantle ± Asthenosphere

± LithosphereCrust



The difference between the mantleand the crust is based on chemical

composition.The difference between theasthenosphere and the lithosphere is

based on viscosity -the ability to flowunder pressure.)



EvidenceEvidenceWhat evidence do we really have that the

interior of the earth is the way we think it is?

Deep mines are hot!H eat and molten material escape fromvolcanos and geysers.

Earthquake waves



Earthquake WavesEarthquake Waves

When an earthquake occurs itproduces 2 types of waves:

± P or primary waves. These are wavesof compression of the rock. They travelfastest.

±S for secondary or shear waves. Therock moves up & down or sideways.



Earthquake wavesEarthquake waves

P waves are capable of traveling throughthe mantle and cores.

S waves can¶t travel through liquids, theystop when they hit the outer core.



C ornell Univ.



Earth¶s Magnetic FieldEarth¶s Magnetic Field

In the earth, electrical currentsrun through the molten core.



Earth¶s Magnetic FieldEarth¶s Magnetic Field

The electrical currents within the earthcause earth to act like a giganticelectromagnetic generator.

This is called the Dyn amo Theor y of Mag n etic Field Ge n eratio n .



Magnetic Field StructureMagnetic Field Structure

The whole magnetic field iscalled the mag n etosphere .



The magnetic field channelsaway the solar wind.

Prevents erosion of theatmosphere.



Solar WindSolar Wind

±Extremely hot, high-energy, chargedparticles given off bythe sun.



H ow does the magnetic fieldH ow does the magnetic fieldprotect us?protect us?

The magnetic field capturesthe solar wind and channels it

around the earth.

This is called the Van AllenRadiation Belt (V.A.R.B.)



The AtmosphereThe Atmosphere

Earth¶s atmosphere is unlike any other planet¶s in chemical composition.



Chemical Composition ChemicalChemical Composition ChemicalCompositionComposition

Our current atmosphere is :78% nitrogen (N)

21% oxygen (O)

1% argon (Ar), helium ( H e), carbondioxide (CO 2), water vapor ( H 2O),and about 20 other rare gases.



Atmospheric Pressure Atmospheric Pressure

Pressure - downward push of thecolumn of air above you.

At earth¶s surface, the air pressure is 14.7 pounds / squareinch.Other units are 29.92 inches of mercury in a barometer.



The Atmosphere¶s StructureThe Atmosphere¶s Structure

Earth¶s atmosphere has both v erticala n d horizo n tal structure.Vertically, the atmosphere is dividedinto 4 la yers.H orizontally, the atmosphere isdivided into 6 circulatio n cells , 3 inthe northern hemisphere & 3 in thesouthern.



4 Layers4 Layers

Troposphere - weather layer.From the earth¶s surface to 10km up . It gets colder the higher

up you go.

Stratosphere - circulation layer.The jet stream a n d ozo n e la yer are in this layer



M esosphere - a middle layer, upto 75 km . H ere the air pressureis only 1/10,000 th of the pressureat the earth¶s surface.

.Thermosphere - the hot layer,up to 120 km . This is the outer edge of earth¶s atmosphere.



H ow does the atmosphere affectH ow does the atmosphere affectthe surface?the surface?

« in 4 ways:35% of the sunlight that hitsthe atmosphere is reflectedback into space by clouds.




33% of the sunlight isabsorbed by gases and dust,but then is re-radiated asinfrared (heat). Much of this

infrared light goes back intospace and is lost.




Dust in the atmosphere alsocauses redde n in g , a process

where the blue light isscattered, but red light isallowed to pass straightthrough.



Thereddening

effect.



Atmospheric Circulation Atmospheric Circulation

Earth¶s atmosphere has

3 circulation cells in eachhemisphere



How does the air circulate?W arm air rises at the

equator, cools off at highaltitude , then falls back tothe surface at 30 o north

latitude. It eventuallycirculates back to equator.



Atmospheric Circulation Atmospheric Circulation

The earth¶s rotation causes theC oriolis Effect . This causesmoving wind to turn or deflect tothe right in the northernhemisphere. The circulation

allows winds to move all the wayaround the globe .



Where did the atmosphere comeWhere did the atmosphere comefrom?from?

Some water and gases

were contributed bycomets, meteors,

impacti n g o n earth¶ssurface .



Where did the atmosphere comeWhere did the atmosphere comefrom?from?

But most of the atmospherecame from v olca n icoutgassi n g . Volcanoesrelease over 100 billion

kilograms of water vapor andgases into the atmosphereevery year.



Earth has had 3 atmospheres.1 st atmosphere

The first atmosphere wash ydroge n (H) a n d helium (He)from the original nebula.These gases were eventuallylost to space.



2 2 nd nd atmosphereatmosphereH eavy gases were leftbehind: n itroge n (N2)a n d carbo n dioxide(CO 2).



33 rd rd atmosphereatmosphere

P hotos yn thetic

bacteria use theCO

2, &produced ox yge n (O 2).



Earth¶s GeologyEarth¶s Geology

Earth¶s surface changes by :Erosio n a n d build upstructures .Flowi n g water Flowi n g ice or la v a .Subsurface mo v eme n ts of tectonic plates.

earth: the model planet

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