a1_10n11_Earth_v2 - The Starting Point for Comparative...

Planet Earth: Home
The Starting Point for Comparative Planetology

Some basic numbers
 Semi-major axis: 1.00 AU (92.8 million miles, 150 M km)
 Orbital Eccentricity: 0.0167
 Orbital Inclination: 0.0 degrees (by definition)
 Orbital Period: 365.26 days
 Sidereal rotation period: 23h 56m 3.8s (24 hr wrt the Sun)
 Diameter 12,756 km (~ 7900 miles)
 Density: 5.5 g/cc (4.2 uncompressed)
 Mass (Earth = 1): 1.0 (5.9 x 10
24
kg)
 Obliquity: 23.45 degrees
 Number of satellite: 1
 Surface temperature: -50 to +50 C (-60 to 120 F)
 Albedo (cloud tops): 0.36
 Atmospheric Pressure at surface: 1013 millibars

Earth has lots of
surface water, a paper
thin, oxygen-rich
atmosphere,
a relatively strong
magnetic field, and a
very active crustal
plate system which
generates volcanoes,
earthquakes, and deep
ocean trenches.

Four Stages of Planetary
Development
• Differentiation: formation of a dense core and
lighter outer layering
• Cratering: a `brief’ period of heavy bombardment
of meteorites and asteroids hitting the newly
forming planet
• Flooding: radioactive decay heats up the planet
creating floods of lava and lava-filled basins
• Surface evolution: slow processes that changes
the planet’s surface features.

All the terrestrial planets were once molten
(at least partially) and maybe even molten twice.
The heavier materials sank towards the interior
while the lighter materials rose to the surface.
Differentiation

Earth ʼ s interior
nickel-iron rich core
rock mantle and
crust
Planet ʼ s Mass
Crust 00.4%
Mantle 67.1%
Core 32.5%

A cross-section of the Earth interior
.

The Earth’s interior has been deduced mostly
through the study of earthquakes.
Seismology

P
S
We know the outer
core of the Earth is
liquid because shear
(S) waves don ʼ t
penetrate that
portion of the Earth ʼ s
interior.
Only pressure (P)
waves do.
So there ʼ s a S wave
shadow opposite an
earthquake site.

The Earth ʼ s increasing interior temperature with depth
creates a molten outer core….which is then re-solidified
with the enormous pressures at even greater depth.
“ Pressure Freezing ”
Why is only the outer portion of the core molten?

Earth ʼ s Variable
Magnetic Field
At the moment it's located
in northern Canada, about
600 km from the nearest
town: Resolute Bay,
population 300.

Scientists have long known that the magnetic pole
moves. It was pinpointed first by James Ross in 1831
near the end of a grueling expedition in which his ship
got stuck in the ice for four years. In 1904, Roald
Amundsen located the magnetic pole again and
discovered that it had moved--at least 50 km since the
days of James Ross.
The pole kept going northward during the 20th century,
north at an average speed of 10 km per year, lately
accelerating to 40 km per year.
At this rate it will exit North American waters and reach
Siberia in a few decades.

Earth's magnetic field is changing in other ways too.