Evidence for Early Earth

In order to think about the formation of Earth, there are some assumptions that must be made.

• Earth today is cooler than early earth.

• Natural disasters such as volcanoes and earthquakes were occurring.

• That gases coming from volcanoes, thermal vents, and geysers are similar to those leaving the earth’s crust today.

• Assume asteroid belt is left over from planet building.

What we do know…

• We know that matter has a gravitational pull on other matter irregardless of size.

• As objects travel through space they are attracted to each other and can (and do!) collide into each other.

• Impact craters are the scars left over from these many impacts.

• Know about radiometric dating and half-life of elements so can determine approximate age of rock samples.

Asteroid EvidenceAsteroid Evidence

Some meteorites that have Some meteorites that have fallen have a high carbon fallen have a high carbon content, as well as high water content, as well as high water content.content.

Can determine age of Can determine age of meteorites and, therefore, of meteorites and, therefore, of Earth. Earth.

Found meteorites to be about Found meteorites to be about 4.5 b.y.o.4.5 b.y.o.

Inference: Inference: (Age of Earth about 4.5 b.y.o.(Age of Earth about 4.5 b.y.o. Asteroid impact can have Asteroid impact can have

disastrous consequences: huge disastrous consequences: huge fires & climate changes)fires & climate changes)

Liquid Interior of Early EarthLiquid Interior of Early Earth Earth was constantly bombarded with debris due to Earth was constantly bombarded with debris due to

gravitational pull. gravitational pull. Heat, due to friction, would be generated whenever Heat, due to friction, would be generated whenever

objects hit Earth.objects hit Earth. Radioactive elements in Earth produced more heat (we Radioactive elements in Earth produced more heat (we

know that radioactive elements produce heat when know that radioactive elements produce heat when decaying….that’s why nuclear power plants must be decaying….that’s why nuclear power plants must be cooled).cooled).

Not much Iron on the surface of Earth.Not much Iron on the surface of Earth. Inference: Inference: (heat melted elements and the heaviest, like iron, sunk (heat melted elements and the heaviest, like iron, sunk

to center and lighter elements, like carbon and water, to center and lighter elements, like carbon and water, floated to the outer layer. Called the Iron Catastrophe)floated to the outer layer. Called the Iron Catastrophe)

Our Moon

• Apollo astronauts collected rocks from moon whose ages were calculated using radiometric dating.

• Rocks were much younger than Earth.• Same chemistry as the Earth but different than

anything else in solar system.• Inference: • (Early Earth didn’t have moon and moon came

from Earth)

Our Moon Gravitational interaction between Earth& Moon:

• We have been measuring the distance of the moon from Earth and we know that it is moving farther away.

• Moon affects large bodies of water: tides of oceans and great lakes

• Inference:• (Early earth more affected by

moon than today)

Interior of Earth Today: Evidence Interior of Earth Today: Evidence from Behavior of Earthquake wavesfrom Behavior of Earthquake waves

DepthDepth Primary Primary waveswaves

Secondary Secondary waveswaves

2900 2900 kmkm

Change Change direction direction andand

speed: these speed: these waves travel waves travel slower in slower in liquid than liquid than solidsolid

Bounce off Bounce off (reflected): (reflected): these waves these waves cannot cannot travel in travel in liquidliquid

InferenceInference: outer core is liquid: outer core is liquid

5100 5100 kmkm

increase increase speedspeed

InferenceInference: inner core is solid: inner core is solid

Interior of Earth TodayModel• Inner core solid• Outer core liquid• External mantle

Cooling of EarthCooling of Earth

North and South poles migrate a small North and South poles migrate a small distance each year.distance each year.

Caused by swirling motion of molten core.Caused by swirling motion of molten core. Scientists measured the location and have Scientists measured the location and have

found that the migration of the poles is found that the migration of the poles is speeding up.speeding up.

Inference:Inference: (interior of Earth is changing and cooling (interior of Earth is changing and cooling

causing the pole migration to accelerate)causing the pole migration to accelerate)

Continental Drift: Acceptance

Evidence: Paleomagnetism:– Magnetism of Earth &

changing of the poles cause minerals that to orient themselves in the direction of the Earth’s poles when rock formed

– The pole moves, but the path is different for different continents

Inference:• Continents moved

Earth’s Crust - Plate Tectonics• Magnetism of Earth

(changing of the poles): some igneous rocks contain magnetic minerals that would orient themselves in the direction of the Earth’s poles. If nothing had changed, then the orientation of the minerals would be the same; however, studies show that this isn’t the case.

• Inference:• (the continents have shifted

due to interior movement of the earth’s mantle.)

Continental Drift Alfred L.Wegener (1880-1930)

Once upon the time there was one supercontinent called Pangea

Evidence: • Geological:

– filling of Africa and South America along continental shelf

– Mountain ranges in Africa and South America seem like they were connected

Continental DriftEvidence• Fossil records:

– Nearly identical Land-dwelling animals in once-neighboring regions

– Nearly identical trees

• Paleoclimate• Inference:• (Continents have and

are moving)

Earth’s Crust - Plate Tectonics

• Position of most earthquakes and volcanoes

• Boundaries: can see cracks and fault lines in Earth.

Fault lines in Earth’s crust

• After 1906 San Francisco Earthquake

• San Andreas Fault

Ring of Fire

Earth’s Crust - Plate Tectonics• Heat Flow: Measure of

amount of Heat leaving rocks in the earth’s crust.

• Finding that have high heat flow in the areas that are spreading centers and decreasing heat flow as move away from spreading centers.

• Inference:

• (Convection currents are bringing up hot magma to the surface and the earth’s crust is moving.)

Earth’s Crust - Plate Tectonics• Seafloor elevation:

Higher at centers and lower farther away from centers.

• Inference:• (Heat causes materials

to expand and as rock cools and contracts the elevation decreases away from the centers.)

Conclusions

Earth

Physical Structure Asteroid Impacts Convection Currents

Liquid Ball

Iron Catastrophe

Interior and Exterior Cooled

Moon Formation Magnetic Poles Shifting

Continents moving (Plate Tectonics)

Climate Change effects living organisms

Orbit moving away from Earth

Less tidal pull