Formation of the Earth
Seeing that New Hampshire is
located on Earth, let’s concentrate now on our planet’s development.
Earth is one of the inner planets and is made
up of the denser (heavier) elements that were left over after the Sun
was
formed. The current accepted theory for planet development is known as
the Accretion Theory.
To accrete is to gather together or add on to. Sometimes it is easier
for some people to think of the Accretion Theory as the ‘Snowball
Theory’. Smaller lumps of planet building material were gravitationally
attracted to larger chunks of planet building material and they
collided; much like gathering a bunch of smaller snowballs together to
make a larger snowball.
Collision Course
Very early on in
our Solar
System’s history, there were many more planets than there are today,
though
they were all smaller than today’s planets. The nine planets (and their
moons)
are the bodies that ‘won’ the collision contest. The collisions haven’t
stopped,
they have just slowed down and most of the larger planet-sized chunks
have
been swallowed up (thank goodness, as you will see).
Meteors
Approximately ten tons of new
material enter the Earth's atmosphere every day. Most of this debris is
the size of a grain of sand or a small pebble and burns up harmlessly
in the atmosphere. At night the debris is often visible as shooting
stars. Scientists call these pieces of planet building material that
burn up in our atmosphere, meteors. After
they burn
up on entry into the earth’s atmosphere, their dust settles on the
surface of the Earth.
Leonid
Meteor Showers |
The Leonid Meteor Showers happen when the Earth
passes through the tail of Comet Temple-Tuttle. When the Earth passes
through the comet's tail, all the dust and debris of the comet burns up
in our atmosphere and is visible as meteor showers in the
night sky. The Comet Tempel-Tuttle has an eliptical orbit around the
sun.
Most of its orbit is in the outer solar system. It enters the inner
solar
system and passes by Earth every 33 years. The next pass-by of the
comet
will occur in 2033.
(Click
on the image for a closer look.)
Picture Credit: NASA,
Hubble Space Telescope
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Meteorites
Sometimes larger chunks survive
the burning trip through the atmosphere and hit the surface of the
Earth. These are called meteorites.
Fortunately, most of our planet’s surface is ocean, so meteorites tend
to land harmlessly out at sea. On rare occasions, city sized chunks of
rock and/or ice slam into Earth and cause massive destruction.
Scientists believe a large meteorite that hit the Yucatan Peninsula in
the Gulf of Mexico 65 million years ago at the end of the Cretaceous
period led to the extinction of the dinosaurs. They think that when the
meteorite hit the Earth, it sent huge quantities of dust, smoke and
debris into the atmosphere all over the world. The dust, smoke and
debris blocked the Sun for many weeks or months. This caused
temperatures to drop all over the planet, causing winter like
conditions everywhere. Plants and animals that couldn't adapt to the
sudden changes in
light and temperature died, and animals that depended on these
organisms for
food, like the dinosaurs, eventually died as well.
Friction
The friction of huge impacts
creates heat. The relentless pounding the early Earth took generated so
much heat that it melted the entire planet into liquid rock. Yup,
the Earth was a floating ball of lava in space!
Feel the Heat
Try the simple experiment of
rubbing your hands together briskly for ten to twenty seconds and feel
the heat generated from this relatively miniscule amount of friction.
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Forming Layers
While
the Earth was molten, it separated into layers, like oil and vinegar
salad dressing does when it
is undisturbed. The heavier elements settled towards the center of the
planet,
the lighter materials floated on top (Click on the image for a closer look.)
and those Image
Courtesy
of Windows to the Universe, at:
materials whose http://www.windows.ucar.edu/
densities lay
between these two extremes were settled between the heaviest and
lightest
two layers.
The core separated into a solid
inner core consisting mainly of iron and nickel. The inner core is
surrounded by a liquid metal outer core that generates an electrical
current as the Earth rotates. This spinning electrical current is
responsible for the magnetic field that surrounds our planet. This
magnetic field protects us from some of the more deadly forms of solar
radiation by deflecting those harmful rays towards the North and South
Magnetic Poles and in doing so, create the Northern and Southern Lights.
As the bombardment of larger
chunks slowed down, the exterior of the earth had a chance to cool and
harden into a crust as it was exposed to the coldness of outer space
(there was no atmosphere in the early part of the Earth formation).
The mantle stayed molten because
the
crust served as insulation retained the heat generated from radioactive
materials
in the Earth’s interior.
The mantle doesn’t just sit
there, it is in constant roiling motion due to convection of the
liquid rock. The term ‘liquid’ here is slightly misleading. A more
accurate description of the consistency of the earth’s mantle just
below the crust is more like that of a taffy that is sticky enough to
grab a hold of the rough and uneven underside of the crust and pull the
crust along with it. This constant tugging at the underside of the
crust by a thick, sticky substance sometimes results in separation or
rupturing of the crust which might allow for the liquid rock to ooze
through to the surface. But that story belongs in the section
on Plate Tectonics.
Creation of the Moon
Fitting
right in with the Accretion Theory, the Giant Impactor Theory suggests
that an object the size of Mars hit the still- forming Earth 4.5
billion years ago. When this object hit, it sent large abounts of
superheated material from
(Click
on the image for a closer look.)
the outer layers Image
Credit: William K. Hartmann
of both bodies into
orbit around the Earth. This molten debris formed a ring around the
Earth. The debris in the ring eventually stuck together to form the
Moon. Supporting evidence for this theory includes:
- a lunar orbit that is
slightly tilted in respect to Earth’s equator (An Earth and Moon that
developed together side by side would most likely have had the Moon
orbiting right over the earth’s equator. Actually, this would
have been cool because there would
have been a lunar and a solar eclipse every month! However, due
to
the slight orbital tilt of the Moon, most times the Moon travels above
or
below the Sun as seen from Earth – so no solar eclipses, or it travels
above
or below Earth's shadow in space - so no lunar eclipses each month
either.
As a result, eclipses only happen once in a while when the Earth,
Moon
and Sun line up just right, as opposed to every month.);
- the Moon is moving away from
the Earth at the rate of about an inch a year. As a result, the Moon is
about a yard farther away from the Earth now than when Neil Armstrong
walked on its surface;
Lunar rocks are very similar to some Earth rocks. This is most
likely the result of some material
from both bodies in the collision mixing together.
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