The Earth Moon SystemFormation, Development, and Current State

We were wrongIt was once believed that Earth was created, instantly, 6000 years ago.Ancient thinkers like Aristotle and Leonardo da Vinci saw fossils as evidence the Earth was much older.Lord Kelvin used heat to determine an age of 24-400 million years oldArthur Holmes was the first to get a near accurate age of the Earth using, determining the earth to be about 1.6byo using radioactive decay.Later, improved methods of radiometric dating led to a much more accurate age of the Earth.

FormationAbout 4.5 billion years ago, Earth, along with the other planets in our solar system began to take shape.They formed in accretion disks.The material that formed the Earth was created in supernovas.

Proto-EarthWithin 10-20 million years Earth, slightly smaller than today, had formed from the accretion disk located about 150,000,000km from the sun.It is hypothesized that another, even smaller planet was also forming at about the same distance.This planet, Theia, was about the size of Mars.

Giant Impact HypothesisShortly after the formation of these two planets, Theia struck Earth with a glancing blow.This impact liquefied Earth and ejected a large amount of molten material.The ejected material formed the Moon.The remainder of Theia sunk to the center of Earth to help form its iron core.http://upload.wikimedia.org/wikipedia/commons/d/d1/Big_Slash.gifThere are some other, less likely ideas as to how the Moon formed

Co-Formation HypothesisBefore, we visited the Moon and were able to analyze its contents, it was thought that the Moon formed at the same time and location as Earth. This would have left the Moon rotating directly above the equator with much more Iron than it currently has.

Fission HypothesisIt was also once believed that centrifugal forces pulled a chunk of earth out into space leaving a basin behind which later formed the Pacific Ocean.This would have required the Earth to be spinning much faster than it does today.It also would have formed the Moon rotating directly above the Equator.These facts make this an unlikely hypothesis.

Capture HypothesisBecause the Moons orbit is not directly above the equator, it was once believed that the moon was formed elsewhere in the Solar System and later captured by Earths gravity.For this to have occurred the Earth would have needed a much larger atmosphere to slow down the approaching Moon.This too is very unlikely.

ExplanationThe Giant impact Hypothesis is the most likely because it helps explain other features about the Earth Moon system.Large amount of Iron in the coreStill molten mantleTilt of the EarthSpeed of Rotation of Earth

A Changing Planet Time Line4.5 bya - Magma Earth4.4bya - Ocean EarthCarbon dioxide atmosphere, iron rich oceans3.4bya - Continents formGranite floats on magma2.2-1.5bya - Blue PlanetStromatolites release oxygen that turns oceans and sky blue.

Time Line (cont)1.0bya RodiniaSuper-continentTrilobites best evidence700mya Snowball EarthCaused by massive super-continent630mya Cambrian ExplosionShallow seas allows for evolution of a wide variety of lifeEvidence found in Burgess Shale

Time Line (cont)300mya - Animals/Plants moved on landOxygen in atmosphere created ozone that protected animals and plants from UV rays250mya - Massive volcanic eruptionsLed to extinction of 95% of living thingsCreation of Pangea235mya - Dinosaurs began to ruleLukewarm blooded, allowed them to survive in hot, oxygen rich environment.

Time Line (cont)180mya - Pangea breaks up.Dinosaurs survive65mya - KT BoundaryAsteroid/Comet impacts MexicoVolcanoes erupting in IndiaMost dinosaurs go extinct

Time Line (cont)50mya - Mammals began to flourishUplift and Erosion shape surface of Earth2mya - Human ancestors leave AfricaIce Ages send glaciers back and forth across the continents10,000ya - Last Ice Age retreatsHuman civilization begins

The Future+15000y - New Ice AgeWithin the next 15000 years a new Ice Age will begin.+200my - New Super-Continent forms+2by - Mantle and Core coolStops tectonic movementStops magnetic field

EarthEarth is the 5th largest planet.12,800km diameter.Not a perfect sphereCentrifugal force makes the circumference around equator bigger than circumference around poles. (difference of 67km)Oblique Spheroid

Earths AxisEarths axis is an imaginary line that runs through the Geographic North and South Poles.The Earth spins about this axis once every 23hours 56minutes.The axis is tilted at an angle of 23.5 from vertical.This tilt is responsible for the seasons.

SeasonsThe seasons have differing weather patterns for two reasons1. The angle of the Suns rays varies from most direct in the summer (hotter) to least direct in the winter (cooler)2. The length of day varies from longest in the summer to shortest in the winter, giving the Suns rays less time to warm the Earth.The Northern and Southern Hemispheres have opposite seasons.

SolsticesThe solstices occur on when the amount of daylight is the greatest or least and the angle of the Suns Rays are the most or least direct.Winter Solstice - December 21stSummer Solstice - June 21st

EquinoxesAn equinox occurs when there is exactly 12hours of daylight and the Suns rays are pointing directly at the equator.Spring Equinox - March 21stFall Equinox - September 23rd

Earths StructureEarth is comprised of several layers.These layers are separated due to their density.CrustUpper MantleLower MantleOuter CoreInner Core

CrustThe Crust is the layer of the Earth we all walk on.0-35km below the surface of the Earth.Two different types Granite Crust - Covers continents, thickerBasaltic Crust - Ocean Floor, thinnerCrust contains rock in all phases of the rock cycle.

MantleThe Mantle is the area of rock between the core and the crust. (35-3000km)The rock is plastic in characteristic and flows too slowly to be considered a liquid.The difference between the upper and lower mantle is due to the way seismic vibrations pass through.Seems to be pressure related.

Outer CoreLiquid layer of Iron and Nickel located between the inner core and the lower mantle.3000-5000km deepPredominantly responsible for Earths magnetic field due to the rapid movement of the liquid metal.

Inner CoreThe center of the Earth.Solid alloy of nickel and iron.5000-6400km deep Thought to be hotter than the surface of the sun. (Remains solid due to immense pressure)

Earths Magnetic FieldAs a result of the rapidly spinning liquid metal found in the outer core, Earth has a magnetic field, similar to a giant bar magnet.This magnetic field protects us from harmful rays and particles emitted from the sun.

Magnetic PolesJust like a bar magnet, Earth has magnetic north and south poles.A compass is a small magnet that aligns its self to Earths magnetic field, always pointing to the North and South Magnetic Poles.A compass above either magnetic pole will point in random directions.These poles do not align with Geographic poles.They can move up to 15km a year.

The MoonThe Moon is Earths only natural satellite.It is the fifth largest moon in the Solar System.The Moons orbit ranges from a distance 363,000km to 406,000km.The moon is about 3500km in diameterThis gives the moon roughly 1/6th the gravity of here on Earth.

Moon (cont)The moon takes 27.3 days to orbit the Earth.As the Earth is also moving during this time the Moon completes its cycle of phases over a period of 29.5 days.

Structure of the MoonLike Earth, the Moon has a crust, mantle and core.Unlike Earth, only a small portion of the Moons core is still liquid. The Moon has cooled significantly since it was formed.

Surface of the MoonThe Moons surface has several important features.Maria - dark, relatively featureless plains on the moon.Formed as lava filled depressions left by impacts.Terre - Lighter colored highlands of the moonMountains exist only around the edges of Maria and were not formed by tectonic movement.

Surface of the Moon (cont)Regolith - the soil of the MoonResult of many impacts breaking up rock into very fine particles.Maria has 3-5m of regolith, Terre has 10-20m.Impact Craters - form as asteroids, meteors, and comets impact the Moon.Lack of atmosphere leaves these craters undisturbed.

Motion of the MoonIf we could view the Earth moon system from above the North Pole, the moon would rotate around the Earth counterclockwise.It also rotates once about its axis, again in a counterclockwise motion.

TidesOne of the most obvious effects of the relationship between the Moon and Earth are tides.Tides are the result of the gravitational pull of the Moon and the Sun on Earths oceans.They can cause the level of the ocean to change as much as 17 meters depending on the location

TypesThere are two types of tides.Spring tides occur when the Moon, Earth and Sun form a straight line.These tides are the most extreme, highest and lowest.Gravity of Sun and Moon work together.Neap tides occur when the Moon, Earth, and Sun form a right angle.These tides have the least variation between high and low tide.Gravity of Sun and Moon are work against each other.

Sides of the MoonBecause the Moon rotates exactly once for each revolution around the Earth, the same side of the Moon always faces the Earth.We call this side the Near Side of the Moon.The Far Side of the moon is often incorrectly called the Dark Side of the Moon.The Far Side of the moon has almost no Maria.Likely due to lack of tidal forces from Earth.

Phases of the MoonLike any sphere lit by a single source, half of the moon is always dark.As the Moon spins around Earth, we see varying amounts of this lit portion. When the amount of the lit Moon we can see each night is getting larger the moon is considered to be waxing.The Moon is considered to be waning as the lit portion decreases each night.

New MoonThe new moon occurs as the moon is between the earth and the sun.The new moon is not visible.It rises and sets with the sun.

Waxing CrescentIs the phase in between the New Moon and the First QuarterThe edge of the Moon is on the right.They rise between sunrise and noon and set between sunset and midnight.

First QuarterThe First Quarter occurs when the Moon and the Sun form a right angle with Earth.The curved side of the Moon is on the right.Rises at noon and sets at midnight.

Waxing GibbousOccurs between the First Quarter and the Full Moon.The more rounded side is on the right.Waxing Gibbous moons rise between noon and sunset, and set between midnight and dawn.

Full MoonFull Moons occur when the Earth is between the Moon and the Sun.Full Moons rise at sunset and set at sunrise.A Blue Moon occurs when there are two Full Moons in one month.

Waning GibbousThe phase between a Full Moon and the Last Quarter. Gets a little smaller each night.The more rounded side is now on the left.Rises between sunset and midnight and sets between sunrise and noon.

Last QuarterLast Quarter occur when Moon Earth and Sun form right angle.The round side of the Moon is on the left.Rises at midnight and sets at noon.

Waning CrescentPhase between the Last Quarter and the New Moon.Edge of moon on the leftRises between midnight and sunrise, sets between noon and sunset.

EclipsesAn eclipse occurs as the shadow of the Earth or Moon blocks the sun from the other.Because the Moon revolves around Earth at a slight angle, and is quite a distance from Earth, rarely does the shadow of one obscure the other.

Solar EclipseSolar Eclipses occur as the Moon casts a shadow on the Earth.The Moons shadow has two partsUmbra - darker, center part of the shadowPenumbra - lighter outer part of the shadowAn area that lies in the Umbra will see a full solar eclipseAn area that lies in the penumbra will see a partial solar eclipse.

OccurrenceMust occur during the New Moon phase. They occur somewhere on Earth about every 18 months.A total solar eclipse occurs in any given area of Earth about once every 370 years.As the shadow moves at 1700km/hr totality only lasts for at most 7.5 minutes.

Lunar EclipseA lunar eclipse occurs as the Moon passes through the Earths shadow.Like solar eclipses, lunar eclipses vary according to the part of the shadow that Moon passes through.As the shadow occurs on the Moon it can be seen from the entire hemisphere that can view the Moon.Because of this Lunar Eclipses are seen more frequently