Origins and Structure: Earth and It’s Oceans

Unit 1: Chapter 2 in Garrison 6th Edition

A Timeline of Earth’s History

Humankind appears

Fig. 1.12, p. 12

The Milky Way is not just a candy bar…Our galaxy is called the Milky Way and is

composed of stars, dust, gas and other materials held together by gravity.

Stars are composed of incandescent gases.The sun is a starEarth was formed by stars

The Life of a StarLife: An area of spinning nebulae (clouds of gas and dust) begins to shrink and heat up. Protostar forms as it flattens and condenses at the center into a knot of gases Nuclear fusion, hydrogen fuses to form helium, begins at 10 million degrees Celsius = energyWe now have a star, stable and no longer shrinking or

expanding. Source of food = hydrogen fuelJob = convert H into other elements like O and CDeath begins as it consumes these C and O atoms.Extreme temperatures can form atoms up to the mass

of iron

Collapse of a StarWithout hydrogen the star begins to collapse

on itself increasing the internal temperature.Intense compression causes an extreme

expansion = SupernovaThe star is blown to bits and the shattered

mass expands outward.Almost the speed of light, 30 seconds

beginning to end Now can from atoms heavier then iron.Earth was an indirect result of a supernova

explosion

The Formation of EarthThe Big Bang – approximately 14 BYA

Mass and energy began to expand from a geometric point.

Evidence: Galaxies are still moving away from us at a speed proportional to their distance.

Early Universe expanded and began to cool. Cooling allowed for the formation of atoms,

such as hydrogen which is the most abundant form of matter still today.

Solar Nebula: Our Special EventThin cloud struck by a supernova causing two

important events:1) Condensing mass began to spin

2) The nebula absorbed heavier atoms passing by.

This now spinning mass became our solar system….inner most portion = sun (protosun)

outer material = planets (protoearth)

The Sun and planets formed by accretion(smaller particles in the spinning nebular cloud

clumping together to form larger objects)

Formation of the Solar System: Nebular Hypothesis

Birth of PlanetsAccretion (30 to 50 million years) = clumping of

small particles into larger masses.First to form: Jupiter, Saturn, Uranus, and Neptune Why? Cooler temperatures allowed methane and ammonia ices to congeal

together.Higher temperatures near the protosun allow

solidifying of metals and some rock minerals ex) Mercury which is mostly iron.Earth with an array of elements is somewhere in

the middle.

A sun and solar system is bornOur sun begins to fuse hydrogen into helium,

and is no longer considered a protosun.Solar radiation “blows” away excess

particles, which is now only seen in the areas surrounding the outer plants.

Earth Accretion and “Iron Catastrophe”

Fig. 1.8, p. 8

Most of the water is here

We are here

A Changing EarthEarly EarthHomogenous mixture of colder particlesEarth’s surface heated up by impact of asteroids,

comets, and other falling debris.Heat and gravitational compression causes certain

elements to accumulate internally and parts of Earth begin to melt.

Density Stratification (4.6 bya)Iron and Nickel internally increased temps = CoreOther elements, silicon, magnesium, aluminum,

and oxygen-bound compounds rose to the surface = Crust

A Changing EarthCoolingAnother planet crashes into Earth causing

the metallic core to combine with Earth’s core.

Rocky mantle was ejected to form a ring of debris, which condensed to form our moon.

Initial atmosphere burned up by the sun, this allowed contained gases to form a second atmosphere.

Outgassing = volcanic venting, which included water vapor that later formed clouds.

Formation of the Oceans and Early Atmosphere

Figure 2 – 07

Volcanic outgassingRecently some researchers have suggested that ice meteorites could have been an important source of water, although this view has been challenged.

Oceans = Volcanic Outgassing + Ice-Rich Comets

Fig. 1.12, p. 12

Formation of the OceansEarth still very hot, no collection of water.Thick clouds would not allow the sun to reach Earth.Eventually clouds cooled enough to form water

droplets..quick water cycle did not stay on Earth.20 million years of heavy rains which eventually

deposited minerals and began to collect.Ocean waters and Earth’s crust grew deeper and thicker. Icy comets and asteroids would later contribute to our

oceans as well.Today the ocean continues to expand..0.1 Cubic km per

year.

Changing AtmosphereRich in CO2 , N, Water Vapor, with traces of

ammonia and methane.3.5 BYA mixture begins to change mostly N

and O.

There was no oxygen (it would be made later by photosynthesis), and there were methane, ammonia, and high amounts of carbon dioxide.

The Early Atmosphere:Very Different Than Today’s

Where did Life Begin?

Life begins in the oceanCarbon compounds initiate life. These carbon compounds might have come from

comets and other materials that crashed into our planet. (Miller –Urey Experiment)

Bodies of living organisms are made up of saline water.

Biosynthesis: Organic Compounds to Living Organism

Early oceans were frozen, trapping life, because of a lack of heat given off by the sun. (Good because elements in the atmosphere would have destroyed these simple organisms)

Cyanobacteria

The Origin of Life on Earth• The earliest life forms probably arose in

the oceans.– Lightning? Hydrothermal vents? Outer space?

• The first fossil life forms are primitive bacteria found in rocks >3.5 billion years old! Animals and plants would evolve much later.

The FutureSpeculation: 5 billion year maintained as it is.The sun (star) will eventually die.Not big enough for a supernova, but will

engulf inner planets and eventually the sun will cool.