Transcript A Short Look at Earth History

A SHORT LOOK AT EARTH HISTORY
FORMATION OF UNIVERSE
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Formation of Universe: 13-20 billion years
 Big
Bang Theory
Formation of Galaxy: 11 billion Years
 Formation of Solar System: 4.6 billion years
 Probably takes 10-100 million years for planets
to form
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BIG BANG THEORY
FORMATION OF SOLAR SYSTEM
FORMATION OF SOLAR SYSTEM
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Planets made of same material as Sun, minus
elements that remain mostly in gases
Inner Rocky Planets: iron and magnesium silicates
Outer gas giants and moons: water ice
If a protoplanet gets big enough, it can hold
everything (Jupiter, Saturn)
Very far from sun: methane, ammonia, nitrogen ice
OUR SOLAR SYSTEM MAY NOT BE TYPICAL
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Over 970 (973 as of 9/14/13) extrasolar planets
known
 262
may be habitable planets
Most known are Jupiter-size planets, larger and
easier seen
 Super-Earths actually outnumber giant planets
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OR IS IT TYPICAL?
THE MILKY WAY
FORMATION OF EARTH
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Planets formed by accretion of smaller objects =
impact
Very tiny objects hold together by atomic forces
Objects kilometers across hold together by gravity
How do objects the size of a refrigerator hold together?
As planets get bigger, gravity gets stronger, impacts get
more violent
Big impacts throw out ejecta, trap heat
Magma ocean
Formation of core early in earth history as iron sinks
FORMATION OF EARTH
FORMATION OF MOON
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It's very hard to account for the Moon:
 Very
big compared to its parent planet
 Orbits nearly in plane of earth's orbit, not over
equator.
Co-creation with Earth?
 Fission?
 Capture?
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COLLISION
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Over 4 billion years ago
Can explain why moon orbits in earth's orbital
plane
Can explain why moon's composition differs from
earth
Models of solar system evolution suggest that last
stage is mega-collisions
Impact would have melted most of earth and moon
Earth would have been incandescent for about
10,000 years
COLLISION
UNSTABLE EARLY EARTH
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May have been several moon-forming events
1000-km impactors can melt crust
100-km impactors create temporary atmosphere
of vaporized rock, vaporize oceans
Life not possible until large impacts cease
To have life on Earth, we need Jupiter?
 Sweeps up debris and reduces impacts
 Stabilizes orbits of other planets
To have life on Earth, we need Moon?
 Stabilizes changes in earth's axis tilt
GEOLOGIC TIME SCALE
CONDITIONS ON EARLY EARTH
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Oldest existing earth materials: 4.1 billion years old
Oldest rocks: 3.9 billion years old
Oxygen-poor atmosphere (present oxygen is
created by life)
Faint Early Sun: perhaps 30% less bright
Evidence for liquid water from very early on
ORIGIN OF THE OCEANS
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Earth the Biography: Origin of the Oceans
MAJOR EVENTS IN THE HISTORY OF LIFE
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Oxygen levels in atmosphere
 Plants
release waste oxygen
 Eventually organisms developed a way to utilize
oxygen
Sex: Who Needs It?
 We are a team: Mitochondria
 Snowball Earth: what survived and how?
 Cambrian "Explosion"
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SNOWBALL EARTH
CAMBRIAN EXPLOSION
MASS EXTINCTIONS
CAUSES ?
Climate Change
 Disease
 Mountain-building
 Sea Level Change
 Competing Organisms
 Over-specialization
 Volcanism
 Meteor Impact
 Humans
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EARTH HISTORY
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The Early Earth and Plate Tectonics