Transcript EARTH AS A PLANET

NEW “PLANETOID” - SEDNA
(Inuit Goddess of the Sea)
Current Distance
~100 AU
Perihelion Distance
~75 AU
Mass
~1/2 Pluto
Eccentricity
0.85
Semi Major Axis
~500 AU
Period
11,000 years
Aphelion Distance
~925 AU
Inclination to Ecliptic
12 Degrees
EARTH AS A PLANET
Chapter 7
SOME PROPERTIES of
EARTH
Semi major Axis
1.00 AU
Period
1.00 year
Mass
5.98 x 1024 kg
Diameter
12,756 km
Escape Velocity
11.2 km/s
Rotation Period
23h 56m 4s
Surface Area
5.1 x 108 km2
Atmospheric Pressure 1.00 bar
EARTH as a PLANET
 Only
planet with water in liquid form.
 Composition: iron, silicates, oxygen.
 Density: highest in Solar System.
 Interior: 4 major layers – inner core, outer
core, mantle, crust.
EARTH as a PLANET
 Only
planet with water in liquid form.
 Composition: iron, silicates, oxygen.
 Density: highest in Solar System.
 Interior: 4 major layers – inner core, outer core,
mantle, crust.
 Magnetic Field and Magnetosphere: Earth
behaves as if it had a bar magnet inside it.
MAGNETOSPHERE and VAN
ALLEN BELTS
The MAGNETOSPHERE
SHAPE
EARTH’S STRUCTURE –
HOW DO WE KNOW IT?
SEISMIC WAVES
 Earthquakes
produce two kinds of waves that
travel through our planet.
P
(pressure) waves are longitudinal waves analogous
to those produced by pushing a spring in and out.
 S (shear) waves are transverse waves analogous to
waves produced by shaking a rope up and down.
SEISMIC WAVES
 Earthquakes
produce two kinds of waves that
travel through our planet.
P
(pressure) waves are longitudinal waves analogous
to those produced by pushing a spring in and out.
 S (shear) waves are transverse waves analogous to
waves produced by shaking a rope up and down.
 P waves travel through solids and liquids (5-6
km/s).
 S waves cannot travel through liquids (3-4 km/s).
 Velocity of waves depends on density of material
in which they travel. Velocity is faster in higher
density materials.
S and P WAVE PATHS
FLASHCARD
P WAVES MOVE AT ABOUT 5 KM/S. HOW LONG
WILL IT TAKE A P-WAVE TO REACH THE OPPOSITE
SIDE OF EARTH AFTER AN EARTHQUAKE? (RADIUS
OF EARTH IS 6500 KM)
A) ABOUT 4 SECONDS
B) ABOUT 4 MINUTES
C) ABOUT 40 MINUTES
D) ABOUT 400 MINUTES
EARTH’S STRUCTURE

Under Oceans Crust
6
km thick. Basalts
(volcanic rock, Si, O,
Fe, Al, Mg).

Under Continents Crust
 20
to 70 km thick.
Granite (volcanic
silicates).
EARTH’S STRUCTURE

Mantle
 Down
to 2900 km.
Solid with some
melting.
 Ejected volcanoes
allows study.

Core
 3500 km radius.
 Outer core is liquid.
Inner core dense and
solid.
 Inner core rich in
heavy elements - Fe,
Ni, S.
Crust
Mantle
Outer
Core
Inner
Core
EARTH’S STRUCTURE
 Structure
indicates that
Earth is
differentiated
which suggests
Earth was
once molten so
heavier
elements could
sink to core.
Crust
Mantle
Outer
Core
Inner
Core
PLATE TECTONICS
 Earth’s
crust consists of about 12 plates.
PLATE TECTONICS
 Energy
escaping from the interior drives the
plates (few cm/year).
50 million years
from now
PLATE TECTONICS
 Where
plates interact, dramatic changes occur
in Earth’s crust.

Rift Zones: Plates pulling apart. Material
rises from mantle to fill spaces (volcanoes).
E.g. Mid Atlantic Ridge.
PLATE TECTONICS
 Where
plates interact, dramatic changes occur
in Earth’s crust.

Subduction Zone: Two plates come together,
one forced down and melts. Earthquakes and
volcanoes common along subduction zones.
PLATE TECTONICS
 Coastal
BC is on the upper part of a
subduction zone.
SAN ANDREAS FAULT
ACTIVE SITES on EARTH’S
SURFACE
ACTIVE SITES on EARTH’S
SURFACE
CONTINENTAL DRIFT
FLASHCARD
AT 2 CM/YEAR, HOW LONG WOULD IT TAKE A
TYPICAL PLATE TO TRAVERSE THE PRESENT
WIDTH OF THE ATLANTIC OCEAN, ABOUT 6000 KM?
A) 3 X 106 YR
B) 1.2 X 107 YR
C) 3 X 108 YR
D) 1.2 X 109 YR
> 100 km
Ozone
Layer
Atmosphere very
thin, constant
leakage of H and
He
50 - 80 km, O3,
absorbs UV
radiation
10 - 80 km,
cold (-50ºC),
Stratosphere cloudless
< 10 km, most
atmosphere
Troposphere here. (N2 78%,
O2 21%, Ar 1%,
traces H2O, CO2)
GREENHOUSE EFFECT
 CO2
content of atmosphere is critical for its
role in retaining heat from Sun.
 Greenhouse Effect:
 Earth
absorbs sunlight
and re-emits it as
infrared (IR) radiation
(Earth acts like a
blackbody).
 CO2 transparent to
sunlight but absorbs IR
acting like a blanket.
 The more CO2, the
hotter Earth is.
GREENHOUSE EFFECT and
GLOBAL WARMING
 Greenhouse
effect has raised Earth’s average
temperature by 23ºC.
 Without
the greenhouse effect, Earth’s
average temperature would be below freezing
and Earth would be in a constant global ice
age.
GREENHOUSE EFFECT and
GLOBAL WARMING
 CO2 levels are increasing.
 Prediction: rising CO2 levels
will lead to
global warming with uncertain consequences.
Vegetation map

Rainforests extract CO2

Destruction rainforests

This plus increasing fossil
fuel burning causes
increasing CO2 by 0.5%/yr

Exacerbates Global
Warming

Cf Venus – 700K
LIFE on EARTH
 Earth
is the only planet known to be
harbouring life.
 Life arose early on. Fossils date back 3.5
billion years.
 Origin
of life is unsure.
 Miller experiment:
produced amino acids
and other pre-biological
molecules from
primitive Earth
atmosphere - mainly
methane, water,
ammonia, CO2, no O2.
LIFE on EARTH
 Development
Use
Free
of plants:
up CO2 and produce O2 - photosynthesis.
O2 in atmosphere 2 billion years ago.
 Formation
Protects
of the ozone (O3) layer
Earth from UV.
This allowed life to leave protective oceans
and colonize the land. Not possible earlier.
COSMIC INFLUENCES on
EARTH’S EVOLUTION
 Moon is heavily cratered
 Where are Earth’s
craters?
 Most lost by erosion
and geological
activity.
- caused by impacts.
COSMIC INFLUENCES on
EARTH’S EVOLUTION
 More
than 150 impact craters are still
recognized on Earth’s surface.
METEOR CRATER
0.1 km meteor
Crater size = 10 x
size of impacting object
1.2 km
COSMIC INFLUENCES on
EARTH’S EVOLUTION
 More
than 150 impact craters are still
recognized on Earth’s surface.
COSMIC INFLUENCES on
EARTH’S EVOLUTION
 Concern
is that a large object, ≥10 km, will
collide with Earth releasing a few billion times
as much energy as Hiroshima bomb.
COSMIC INFLUENCES on
EARTH’S EVOLUTION
 Concern
is that a large object, 10 km, will
collide with Earth releasing a few billion times
as much energy as Hiroshima bomb.
 One
such object crosses Earth’s orbit every
100 million years.
ORBITS of the 100 LARGEST
KNOWN NEAR-EARTH
ASTEROIDS
Mean Time to Impact Earth (Years)
IMPACT FREQUENCY
1.00E-12
Impactors on the surface of the space shuttle
1m, 30sec
1.00E-09
Shooting stars
1 mm, 30 sec
1.00E-06
1.00E-03
Meteorites
1m, 1yr
1.00E+00
1.00E+03
Arizona Crater
100 m, 104 yr
1.00E+06
1.00E+09
1.00E-08
Sudbury, Ontario
10 km, 108 yr
1.00E-04
1.00E+00
Diameter (Metres)
1.00E+04
1.00E+08
COSMIC INFLUENCES on
EARTH’S EVOLUTION
 More
than 150 impact craters are still
recognized on Earth’s surface.
METEOR CRATER
0.1 km meteor
Crater size = 10 x
size of impacting object
1.2 km
TUNGUSKA EVENT
Siberia
June 30, 1908
Projectile
exploded before
impacting Earth
Projectile’s mass
estimated to be
100,000 tons
Caused
widespread
damage.
TUNGUSKA EVENT
THE SOLAR SYSTEM
Comets can be captured by Jupiter.
 Actually orbit Jupiter – orbits unstable.
 Comet Shoemaker-Levy9 discovered 1992
 Broke into fragments near “Peri-Jupiter”
 Fragments predicted to crash into Jupiter 1994

SHOEMAKER-LEVY9 COMET
IMPACT
Earth’s
View
Voyager’s
View
SHOEMAKER-LEVY IMPACT
DEVELOPMENT of DUST CLOUD
Impact
IMPACT DUST CLOUDS
IR IMAGE of IMPACTS
Io
COSMIC INFLUENCES on
EARTH’S EVOLUTION con’t
EFFECTS of a MASSIVE
IMPACT
EFFECTS of a MASSIVE
IMPACT
Global earthquakes.
 Huge tidal waves.
 Dust high up in the atmosphere.
 Block out Sun for about one year, kills
photosynthesis.
 World-wide fires, forests and grasslands
destroyed.
 Highly acidic rains.
 Animals depending on plants die
(dinosaurs?), rise of mammals.

EXTINCTIONS, the SOLAR
SYSTEM and our GALAXY

Past 100 million years many large scale extinctions (~
10) identified on Earth.
In these, a significant fraction of existing
species were extinguished.

Best known is extinction
of the dinosaurs 65
million years ago after
flourishing for 100
million years.
EXTINCTIONS, the SOLAR
SYSTEM and our GALAXY

What caused the extinctions?
Impact of ~ 20 km
asteroid.
Evidence: crater in
Gulf of Mexico and
Iridium layer.
EXTINCTIONS, the SOLAR
SYSTEM and our GALAXY

What caused the extinctions?
Impact of ~ 20 km
asteroid.
Evidence: crater in
Gulf of Mexico and
Iridium layer.
Nearby supernova
(depletes O3,
forming NO2).
Crab Nebula
EXTINCTION of the
DINOSAURS
ALTERNATE DINOSAUR
EXTINCTION THEORY
SPIRAL GALAXY
EXTINCTIONS, the SOLAR
SYSTEM and our GALAXY

Supernovae and impacts more likely when Sun passes
through spiral arm in our Galaxy
Oort cloud comets get perturbed.
OORT CLOUD GETS
PERTURBED