Download EARTH

EARTH
OUR HOME IN SPACE
Standards
• Understand the scale and contents of the
universe
• Explain plate tectonics and understand the
evidence that supports it
Earth is best studied terrestrial
planet
• We can draw on our knowledge of Earth to aid
us in our understanding of other planets
Earth Data
Formation of Earth
• Earth formed out of solar nebula
• Formed at same time as other planets (4.6
billion years ago)
• Started out as rocky ball of uniform
composition and density
Earth began to heat & melt
• 3 sources of heat:
1. gravitational collapse
2. radioactive decay
3. bombardment by meteorites
Differentiation occurs
• Differentiation is the formation of layers.
• Heavier elements sank to middle of molten
Earth.
• Lighter elements floated on top.
Layers of Earth (compositional)
• Earth is composed
of three main
layers, defined by
what they are
made of:
1. Core
2. Mantle
3. Crust
Core
• Made of iron & nickel
• Inner core:
 solid – hot, but too much pressure to be

•


in liquid state.
1255 km thick.
Outer core:
liquid – rotates around inner core
(rotation causes magnetic field).
2220 km thick.
Mantle
• Region surrounding core
• Makes up bulk of Earth
• 2900 km thick
• Composed of peridotite (rock containing
iron and magnesium)
• Solid that flows (plastic)
Crust
• Thin, outer layer of Earth
• Solid
Two types:
1. Oceanic crust –
 thinner than continental crust.
 Made of basalt (volcanic rock).
 7 – 10 km thick.
2. Continental crust –
 made of granite.
 20 – 70 km thick.
Other Layers (mechanical)
• Defined by how they behave
• Lithosphere – layer which includes crust
and uppermost mantle.
• Asthenosphere – part of mantle directly
below lithosphere.
How do we know layers of Earth?
• Drilling has only been done to a few km
depth (still in crust)
• Structure known because of seismic
waves.
Seismic Waves
• Vibrations that travel through Earth.
• Produced by earthquakes or explosions on
surface.
• Waves refract (or bend) at boundaries
between layers (because layers composed
of rocks of different densities).
2 types of seismic waves
• Surface waves – travel on surface – not
good for studying interior.
• Body waves – travel through Earth. 2
types:
1. primary or P waves
2. secondary or S waves
Primary or P Waves
• 1st to arrive at seismic
station.
• Compressional wave.
• Can travel through solids
& liquids.
Secondary or S Wave
• Arrive after P waves
• Shear wave
• Can travel through
solids, but not liquid.
• Don’t travel through
outer core  outer
core is liquid
S Wave Shadow Zone
• Zone in which no S waves are recorded by
seismic stations.
Plate Tectonics
• Lithosphere is broken up into segments
(tectonic plates) that move upon the
partially molten mantle – called Plate
Tectonics.
• Movement of plates responsible for many
of Earth’s processes and features, such as
mountains, volcanoes and earthquakes.
• Movement recycles oceanic crust (crust is
created and destroyed).
Tectonic Plate Map
Types of Plate Boundaries
Plates move relative to each other along one
of three types of boundaries
• Convergent boundary
• Divergent boundary
• Transform boundary
Convergent Boundary
• Where two plates collide. 3 Types:
1. oceanic-continental
 oceanic crust is more dense and sinks
beneath continental crust.
 Called subduction zone.
 Where crust is destroyed.
 Cause volcanoes and earthquakes.
Mt. St. Helens
Convergent Boundary
2. Continental-continental
both crusts of same density, so neither
sinks.
Push together and cause mountain building.
Ex: Himalayan Mountains
Himalayas
Convergent Boundary
3. Oceanic – oceanic:
older oceanic crust is cooler and denser, so
the older of the two crusts is subducted.
Forms island arcs, which are volcanically
active.
Ex: Soufriere Hills Volcano, Montserrat (island
in the West Indies)
Soufriere Hills, Montserrat, West Indies
Divergent Boundary
• Where two plates pull apart.
• This is where new crust is made.
• Associated with volcanoes and
earthquakes
• Exs: Mid-ocean ridges
Rio Grande Rift (formed Albuquerque
Volcanoes).
Iceland: Mid-Atlantic Ridge at
Surface and Icelandic Volcano
Transform Boundary
• Where two plates slide
past each other.
• Causes earthquakes
• Ex: San Andreas Fault
San Andreas Fault
Nimitz Freeway collapse during
1989 Loma Prieta earthquake
What Drives Plate Motion?
• Convection in Earth’s mantle – hot
material rises & cool material sinks
• What other body in the solar system has
convection?
• The sun
Other Parts of Earth
• Hydrosphere
• Atmosphere
• Magnetosphere
Hydrosphere
• Includes all the water on Earth that is
contained in the oceans, glaciers, streams,
lakes, soil, groundwater & air.
 The oceans comprise 70% of Earth’s total
surface area
• Water moves between these different
locations through a process called the
hydrologic cycle
Earth’s Atmosphere
• Air above Earth’s surface.
• Breathable by humans
• Mixture of gases:
- 78% nitrogen
- 21% oxygen
- Trace amounts of argon, carbon dioxide &
water vapor
• Large amount of oxygen makes Earth’s
atmosphere unique in solar system.
Structure of Atmosphere
• Troposphere – region where convection
(and weather) occurs. Up to ~12 km in
altitude.
• Stratosphere – contains ozone layer
• Mesosphere – where meteorites burn up
• Thermosphere – topmost layer, above
~80 km. Where aurorae occur.
Layers of Atmosphere
Origin of Earth’s Atmosphere
• Atmosphere of early Earth made up of gases
most common in solar system (hydrogen,
helium, methane, ammonia & water vapor)
• Escaped into space
Origin of Earth’s Atmosphere
• Secondary atmosphere was outgassed
(expelled) from planet’s interior by volcanoes
• Surface temperature fell and water vapor
condensed, forming oceans
• Water in oceans also provided by comets
impacting Earth
• Life appeared in oceans and began to
produce oxygen
• Oxygen in present-day atmosphere is direct
consequence of evolution of life on Earth.
The Magnetosphere
• Zone of charged particles at high altitude,
trapped by magnetic field.
• Completely surrounds planet
• Magnetic N & S poles: where magnetic
field lines intersect Earth’s surface.
Aligned with axis.
• Protects Earth from solar particles.
• Auroras occur when solar wind interacts
with magnetosphere
Life
• Earth is the only known planet to contain
life, and it contains lots of it