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 Evidence  Some meteorites that have fallen have a high carbon content, as well as high water content.  Can determine age of meteorites and, therefore, of Earth.  Found meteorites to be about 4.5 b.y.o.  Inference:  (Age of Earth about 4.5 b.y.o.  Asteroid impact can have disastrous consequences: huge fires & climate changes)

Liquid Interior of Early Earth  Earth was constantly bombarded with debris due to gravitational pull.  Heat, due to friction, would be generated whenever objects hit Earth.  Radioactive elements in Earth produced more heat (we know that radioactive elements produce heat when decaying….that’s why nuclear power plants must be cooled).  Not much Iron on the surface of Earth.  Inference:  (heat melted elements and the heaviest, like iron, sunk to center and lighter elements, like carbon and water, 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 from Behavior of Earthquake waves Depth Primary waves Secondary waves 2900 km Change direction and speed: these waves travel slower in liquid than solid Bounce off (reflected): these waves cannot travel in liquid Inference: outer core is liquid 5100 km increase speed Inference: inner core is solid

Interior of Earth Today Model Inner core solid Outer core liquid External mantle

Cooling of Earth  North and South poles migrate a small distance each year.  Caused by swirling motion of molten core.  Scientists measured the location and have found that the migration of the poles is speeding up.  Inference:  (interior of Earth is changing and cooling 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 ( ) 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 Drift Evidence 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 Liquid Ball Iron Catastrophe Interior and Exterior Cooled Asteroid Impacts Moon Formation Orbit moving away from Earth Less tidal pull Climate Change effects living organisms Convection Currents Magnetic Poles Shifting Continents moving (Plate Tectonics)