Transcript The Earth

The Earth
The Solar System
太陽系
Image Source: moulinlesetoiles
Note: Pluto (冥王星) was recently removed from the list of
planets. In 2006, it was redefined as a dwarf planet.
The Planets to Scale
Our home: just a tiny speck of rock in space?
Inner Planets
Outer Planets
• Mercury, Venus,
Earth, and Mars
• Rocky planets
• Jupiter, Saturn, Uranus, Neptune
• “Gas giants”
The size of the Earth relative to the
Sun
Image source: www.physics.uci.edu
The size of the Sun relative to some
other stars
Image source: www.physics.uci.edu
From our perspective, however, the
Earth has many special characteristics!
• Has largest satellite (moon) compared to its own diameter;
the Moon helps to keep the Earth’s tilt stable.
• Abundant water in the atmosphere.
• At the right distance from the Sun to have liquid water.
• Only planet in the solar system to have open oceans.
Because water can dissolve CO2, the Earth was saved from a
“runaway greenhouse effect.” (Compare with Venus.)
• O2-rich atmosphere (21% O2 by volume)
• Magnetic field that protects the planet from solar wind
• Life! Living organisms cover the Earth. There is no definite
evidence yet for any other biospheres in the solar system…
or, at this point, in the universe….
“Habitable Zone” of Sun –
Distance from a star at which it is theoretically possible for a planet
with sufficient atmospheric pressure to maintain liquid water on its
surface.
Inner edge - 0.95 AU
Outer edge - 1.37 AU
Image Source: DMNS
“The Goldilocks Planet”
Just right!
Illustration: Arthur Rackham
The Earth’s Outermost Layers –
Interconnected Systems
The biosphere
The hydrosphere
The lithosphere (geosphere)
The atmosphere
Image: http://www.gly.bris.ac.uk/www/ESS/index.html
The Earth’s Outermost Layers –
Interconnected Systems
Atmosphere (大氣圈)
• Thin gaseous envelope surrounding Earth
Hydrosphere (水圈)
• Water layer ; most water is in the oceans
Biosphere (生物圈)
• All living things on the planet
Lithosphere (岩石圈) OR Geosphere
• Rocky outer shell of Earth; made of up plates
that have moved through the Earth’s history
Some translate lithosphere as土石圈
(Soil-Rock Sphere)…
• We can’t forget the soil.
• It’s not very exciting, but
our lives depend on it.
• It’s sort of the meeting
place of the four
spheres—the result of air,
water, and organisms
acting on rock.
The Atmosphere (大氣圈)
• Composition is unique in the solar system
78% N2, 21% O2
• Minor amounts of CO2, argon, and water vapor
• O2 is directly linked to the presence of life on
Earth. It is produced mainly by photosynthesis.
Free O2 is very reactive and would not remain in
an atmosphere without life.
The Atmosphere (cont’d.)
The atmosphere makes up only one-millionth of
earth’s mass, but it is VERY important:
• Protects the earth from harmful radiation
• Controls climate; creates a beneficial greenhouse
effect.
• Supports the majority of life forms that need to
take in its gases to live.
The Atmosphere
Image Source: redorbit.com
What kind of radiation does it keep out?
What forms of radiation
reach the Earth’s surface?
The hydrosphere (水圈)
• 75% of the Earth’s surface is covered by oceans
• For the last ~3.8 billion years, the Earth has had a relatively
stable water cycle (see video), with possibly a few freeze-ups
or “Snowball Earth” episodes…
• The planets are misnamed in Chinese: Earth is the “Water
Planet,” not Mercury (水星)!
Liquid water is essential for life as we
know it.
• The biochemical reactions
that sustain life need a
fluid in order to operate;
in a solid, getting
molecules where they
need to go is difficult.
• Compared to most other
liquids, water also has an
extremely large liquid
range.
• Water is probably the
best solvent in the
universe.
It’s hard to imagine waterless life.
Other liquids just don’t work:
• Ammonia (NH3) - liquid range is small, only
about 30 degrees C (compared to 100 degrees
for water)
• Methane (CH4) – a liquid at -150 K, but at that
temperature, other chemical reactions are too
slow…
The Biosphere (生物圈)
• Consists of all life on Earth
• Microscopic organisms are the most common life
forms and are essential for supporting the bigger
life forms. Phytoplankton (microorganisms that live
in water and convert the Sun’s energy into chemical
energy) produce half of the oxygen in the Earth’s
atmosphere. We can’t live without them!
THE BIOSPHERE IS THIN!
For a scale model, take a piece of paper.
Fold once. Paste on a basketball.
The Earth has a layered structure
Compositional Layers
• Crust – Silicates and
aluminosilicates
• Mantle – Silicates rich in
iron and magnesium
• Core – Iron, nickel
Physical Layers
• Lithosphere – Rigid plates
• Asthenophere - Plastic
• Mesophere – Denser, more
rigid than asthenophere
• Outer Core - Liquid
• Inner Core - Solid
地殼
岩石圈
軟流圈
The Earth’s
Layers
地函
中層圈
岩石圈
Image Source: J. Varekamp,
軟流圈
地殼
中層圈
地函
外部地核
地核
內部地核
Let’s start at the Earth’s center and work
outward!
INNER CORE (內部地核)
- HOT!!!! ~9000 C
- Solid
- Composed of Fe and
Ni.
http://www.sciencenewsforkids.org/articles/20030521/a48_1477.jpg
OUTER CORE (外部地核 )
• HOT!
(but not as hot as the
inner core)
• Liquid
• Composed of Fe and Ni
• The Earth's magnetic
field is mostly caused
by electric currents in
the liquid outer core.
http://www.sciencenewsforkids.org/articles/20030521/a48_1477.jpg
The Earth’s Magnetic Field – deflects the
solar wind
Without this field, the solar wind would erode the
Earth’s atmosphere and would shower the Earth with
particles that could damage the DNA of living things.
Artist’s rendering, not to scale.
http://en.wikipedia.org/wiki/File:Magnetosphere_rendition.jpg
MANTLE (地函)
• Still hot! – but not
as hot as the core!
• Largest layer
– 2900 km thick
– 82% by volume
– 68% by mass
• Composed of silicate
rocks with abundant
iron and magnesium
http://www.sciencenewsforkids.org/articles/20030521/a48_1477.jpg
CRUST (地殼)
Two types:
Continental crust
 Thick - up to 75 km
3
 Lower density - 2.7 g/cm
 Strongly deformed
 May be billions of years old
Oceanic crust
 Thinner - about 8 km
3
 Dense - 3.0 g/cm
 Comparatively undeformed
 Younger - < 200 million years
old
http://www.sciencenewsforkids.org/articles/20030521/a48_1477.jpg
The lithosphere (岩石圈) - the outer part
of the earth that consists of rigid plates
Includes the crust and the rigid part of the upper mantle
http://www.physicalgeography.net/fundamentals/10h.html
Main features of plate tectonics
板塊構造學說
• The Earth's lithosphere consists of plates that
are moving relative to one another.
• The ocean floors are continually spreading from
the center and sinking (being subducted) at the
edges.
• Convection currents in the asthenosphere
probably cause plate motion.
• The source of heat that drives the convection
currents is radioactivity deep in the Earth.
The Earth’s Major Tectonic Plates
www.sci.uidaho.edu/geol111/geology_101.htm
(聚合性板塊邊緣)
(分離板塊邊緣)
(轉形斷層)
The Plate Tectonics Model
Convection (對流) in the asthenosphere may drive plate motions;
magnetic “stripes” on the ocean floor record the Earth’s magnetic
field at the time the ocean crust cooled.
Three Types of Plate Boundaries
板塊邊緣
• Divergent (分離板塊邊緣) –
Plates moving apart
• Convergent (聚合性板塊邊緣) –
Plates moving toward each other
• Transform (轉形斷層) –
Plates sliding past each other
Three Types of Plate Boundaries
Plate Boundaries
Image source: Wikipedia
Plate tectonic setting of Taiwan
What kind of plate boundary does Taiwan sit on?
Image from Wang, C.Y. et al. (2001)
Answer: Taiwan sits on a very complicated
convergent boundary
(island arc – continent collision)
If any subduction were occurring we would have a
volcano erupting in Kenting…
Scheme proposed by
Chemenda et al. (2001) for
the arc-continent collision
that produced the island of
Taiwan.
An island arc is not dense
enough to be subducted,
so when it arrives at the
subduction zone,
subduction shuts down.
Geologically dead  Biologically dead?
• Is plate tectonics necessary for life?
• Plate tectonics and liquid water seem to need each
other. If one disappears, so does the other.
• Mercury and Moon – Geologically dead for 4 billion
years…
• Mars – Tectonic activity may have started but was
stopped by the planet’s rapid cooling…
• Venus – Like the very young earth??? The crust may be
too hot for plates to form. Surface of Venus is bone dry
with temperatures near 800o
• Earth – Just right!