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 star
 Earth was formed by stars
The Life of a Star
 Life: An area of spinning nebulae (clouds of gas and
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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 = energy
We now have a star, stable and no longer shrinking or
expanding.
Source of food = hydrogen fuel
Job = convert H into other elements like O and C
Death begins as it consumes these C and O atoms.
Extreme temperatures can form atoms up to the mass of
iron
Collapse of a Star
 Without hydrogen the star begins to collapse on itself
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increasing the internal temperature.
Intense compression causes an extreme expansion =
Supernova
The 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 Earth
 The 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 Event
 Thin 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)
Formation of the Solar System: Nebular Hypothesis
The Sun and planets formed by accretion
(smaller particles in the spinning nebular cloud clumping together
to form larger objects)
Birth of Planets
 Accretion (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 born
 Our 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 Earth
Early Earth
 Homogenous mixture of colder particles
 Earth’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 = Core
 Other elements, silicon, magnesium, aluminum, and
oxygen-bound compounds rose to the surface = Crust
A Changing Earth
 Cooling
 Another 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
Volcanic
outgassing
Recently some
researchers have
suggested that ice
meteorites could
have been an
important source
of water, although
this view has been
challenged.
Figure 2 – 07
Oceans = Volcanic Outgassing + Ice-Rich Comets
Fig. 1.12, p. 12
Formation of the Oceans
 Earth still very hot, no collection of water.
 Thick clouds would not allow the sun to reach Earth.
 Eventually clouds cooled enough to form water
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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 Atmosphere
 Rich in CO2 , N, Water Vapor, with traces of ammonia
and methane.
 3.5 BYA mixture begins to change mostly N and O.
The Early Atmosphere:
Very Different Than Today’s
There was no oxygen (it would be made later by photosynthesis), and
there were methane, ammonia, and high amounts of carbon dioxide.
Where
did Life
Begin?
Life begins in the ocean
 Carbon 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)
The Origin of Life on Earth
•
The earliest life forms probably arose in the oceans.
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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.
Cyanobacteria
The Future
 Speculation: 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.