Earth Formation
by Tega Jessa
One of the oldest questions for mankind is how
the Earth was formed. However, no one has an
exact answer. First by the best estimates it
occurred over 4 billion years ago before any life
appeared. So there are no eyewitness accounts and
other pieces of evidence. The best we can do is
look at the geologic record and the stars to get our
answers. While we may not have the entire picture
we have a good idea and it all starts with how stars
are born.
magma cause volcanic activity that released gases.
These would lead to the creation of the
atmosphere and the oceans starting the water
cycle.
The formation of the Earth was only the beginning
and we still see the Earth changing year by years
through erosion and plate tectonics. However in
learning more about the formation of the Earth we
are able to better understand what makes life
possible on our planet.
Just like the formation of the Earth and other
planets, stars take a long time to be born. Stars are
essentially formed from clouds of gas in space.
We know these as nebulas. You can basically
consider them to be star forges. Over time gravity
causes the atoms of gases and space dust to start
coming together and gathering. Over time this
gather of gases gains more mass and with it
stronger gravity. This is a process that can take
millions of years. In time the gravity causes the
gases, mainly hydrogen to fuse in a nuclear
reaction and a star is formed.
The formation of the Earth occurred after this
initial phase happened for our Sun. After the Sun
was formed we know from observations and other
indirect evidence that there were left over gases
and heavier elements. The gravity of the Sun
helped to flatten these leftovers into a disk and
start to fuse them together. This created the
planetesimals and planetoids which would later
make up the planets. Over time these
planetesimals would collide creating even bigger
masses. It was in this method that the Earth was
eventually formed.
Now we need to know that fusion eventually
creates heavier elements such as carbon and iron.
These elements were to compose a significant part
of young Earth. The pressure and heat from
radioactive decay of elements and the aftershocks
of massive collisions caused the Earth to be
molten. Over time the surface of the Earth cooled
and became the Crust. However the molten layers
that remained became our mantle and the core.
The currents of this massive underground ocean of
The Earth – Part 1 (ART 7.1)
Layers of the Earth
by Fraser Cain
The solid surface we stand on is just one of the
layers of the Earth. In fact, it’s the only one we
can survive on. If you could dig down through the
Earth’s layers, you would find temperatures and
pressure rising to the point that rock melts and
beyond.
Let’s take a look at the Earth layers, starting with
the inside.
The very center of the Earth is known as the core.
This is actually comprised of a solid inner core
with a radius of 1,220 km, and then a liquid outer
core that extends out to 3,400 km. Scientists think
that during the Earth‘s formation, the heaviest
elements – like iron – sunk down to the center of
the Earth and helped to form this core. We know
that the Earth’s core rotates, generating a magnetic
field that protects us from the Sun‘s solar wind.
Nobody really knows how hot it is down there, but
scientists think it’s probably 3,000-5,000 Kelvin.
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Outside the core is the mantle,; the thickest part of
the Earth’s interior layers. This is a vast
underground ocean… of liquid rock! The lave we
see pouring out of volcanoes comes from the
mantle. The heat released from the Earth’s core
drives convection in the mantle, and the crust‘s
tectonic plates serve to stir up the mantle as well.
Hotter material rises, and relatively cooler blobs of
rock sink down through the mantle.
The outermost layer of the Earth is the crust – the
cooled and hardened part of the Earth. That’s what
you’re standing on right now! The depth of the
crust varies from 5 km underneath the oceans and
30 km thick underneath the continents. You might
be surprised to know that the Earth’s crust only
accounts for about 1% of the entire volume of the
Earth.
planet and accumulate at the core. The core is
believed to have two parts: a solid inner core, with
a radius of 1,220 km, and then a liquid outer core
that extends to a radius of 3,400 km. The core is
through to be 80% iron, as well as nickel and other
dense elements like gold, platinum and uranium.
The inner core is solid, but the outer core is a hot
liquid. Scientists think that movements of metal,
like currents in the oceans, create the magnetic
field that surrounds the Earth. This magnetic field
extends out from the Earth for thousands of
kilometers, and redirects the solar wind blowing
from the Sun. Without this magnetic field, the
solar wind would blow away the lightest parts of
our atmosphere, and make our environment more
like cold, dead Mars.
Although the Earth’s crust is cool, the inside of the
Earth is hot. The mantle is only about 30 km
beneath our feet, and it’s hot enough to melt rock.
At the core of the Earth, temperatures are thought
to rise to 3,000 to 5,000 Kelvin.
Since the core is thousands of kilometers beneath
our feet, how can scientists know anything about
it? One way is to just calculate. The average
density of the Earth is 5.5 grams per cubic cm.
The Earth’s surface is made of less dense
materials, so the inside must have something much
more dense than rock. The second part is through
seismology. When earthquakes rock the surface of
the Earth, the planet rings like a bell, and the
shockwaves pass through the center of the Earth.
Monitoring stations around the planet detect how
the waves bounce, and scientists are able to use
this to probe the interior of the Earth.
Core of the Earth
Earth’s Mantle
by Fraser Cain
Scientists believe that deep down inside the Earth,
there’s a huge ball of liquid and solid iron. This is
the Earth’s core, and it protects us from the
dangerous radiation of space.
by Fraser Cain
The ground under your feet might seem solid, but
you’re standing on a relatively thin crust of rock
above a vast ocean of rock. This molten rock is the
Earth‘s mantle, and it comprises the largest part of
the Earth‘s volume.
When the Earth first formed, 4.6 billion years ago,
it was a hot ball of molten rock and metal. And
since it was mostly liquid, heavier elements like
iron and nickel were able to sink down into the
The Earth – Part 1 (ART 7.1)
The crust we stand on is only about 30 km thick.
Out in the oceans, it’s even thinner, getting down
to 5 km in places. Beneath this crust is the mantle
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of the Earth; a region that extends down a depth of
almost 2,900 km.
Although the mantle is largely hidden from our
view, we do see it in places where cracks open up,
allowing the molten rock to escape. These are
volcanoes, of course, and the liquid rock we see
pouring out is the same as you’d find in the
mantle.
The Earth’s mantle is mostly composed of silicate
rocks that are rich in iron and magnesium.
Although it’s mostly solid, it’s hot enough that it
can flow over long timescales. The upper mantle
flows more easily than the lower mantle because
of the increasing temperature and pressures as you
descend into the Earth.
The Earth’s tectonic plates float on top of the
mantle. In some places, the plates are sliding
under one another, returning rock back to the
interior of the Earth. In other places, the plates are
spreading apart, and fresh volcanic material is
welling up to fill the cracks.
Inside the mantle, convection is slowly taking
place – like in a lava lamp. Hotter material, heated
by the core of the Earth rises slowly to the surface
of the mantle. Material cools near the crust and
then sinks back down to the core, to repeat the
process all over again. It’s believed that this
convection helps drive the motions of Earth’s
tectonic plates.
Earth’s Crust
by Fraser Cain
You might not realize it, but you’re standing on a
thin shell of solid rock encasing a vast quantity of
molten rock. This is the Earth‘s crust, and it’s the
part of the planet that has cooled down enough to
solidify. But just a few kilometers below your feet,
it’s molten rock, extending for thousands of
kilometers down to the planet‘s superheated iron
core.
Here on solid ground, on the continental shelves,
the crust of the Earth is about 30 km thick. In the
mid-ocean, the thickness of the crust can be as
little as 5 km. The entire crust occupies just 1% of
the Earth‘s volume.
The crust is composed of a variety of igneous,
metamorphic and sedimentary rocks gathered
together into tectonic plates. These plates float
above the Earth’s mantle, and it’s believed that
convection of rock in the mantle causes the plates
to slide around. On average, rocks in the crust last
about 2 billion years before they slide underneath
another plate and are returned to the Earth’s
mantle. New rocks are formed in the mid-ocean
regions where new material wells out of the Earth
in between spreading plates. In comparison, rocks
in the oceans are only 200 million years old.
The temperature of the crust increases as you go
deeper into the Earth. It starts out cool, but can get
up to 400 degrees C at the boundary between the
crust and the mantle.
Scientists really know very little about internal
structure of the Earth. The crust is the only part
that we have any information about. And we’ve
barely explored it at all. The deepest hole ever dug
was the Russian Kola Superdeep Borehole. Started
in 1970, the hole eventually reached a depth of
12.3 km. They eventually had to quit because
temperatures in the hole became too hot to go any
further. Other plans are in the works to bore into
the crust in the ocean, where the thickness is much
less.
The Earth – Part 1 (ART 7.1)
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The crust of the Earth is not one single piece but is
made up of interacting pieces called the tectonic
plates. This is because the crust sort of floats on
top of the lower layer of the earth made of rock
and magma called the mantle. The convection of
magma in the mantle create the current that causes
plate tectonics forcing different plate to crash or
pull away creating seismic activity.
Crust of the Earth
by Tega Jessa
We know about the crust of the Earth than any
other part of the Earth‘s structure. It is mainly
because this is the layer that we live on and it the
region most easily within our reach. Thought it is
only the “peel’ of the earth we have been able to
learn a lot about the Earth from investigating it.
We know how old the earth is by dating the rocks
and classifying the different kinds that rose to the
surface from the interior of the earth. We know the
fault lines and boundaries of tectonic plates and
where and how the effect the formation of
volcanoes and other geothermal activity.
Scientist believe that the crust was the last part of
the earth to be formed. It is theorized that over 4
billion years ago the Earth was a molten ball. The
denser elements sank to the center of the planet
and became the core. The lighter elements rose
and stratified forming the mantle. The last layer
the crust was formed when the molten exterior of
the Earth finally cooled.
The Earth’s crust can be divided into two distinct
categories. The first is the oceanic crust and the
second is the continental crust. Each has a unique
composition that is different from the other and
the mantle below. The oceanic crust is most made
up of basalt, diabase, gabbro. The continental crust
is made mostly of granite. The thickness of the
crust also varies depending on whether it is the
continental or oceanic crust. The continental crust
can be anywhere from 30 km to 50 km thick and
the oceanic crust can be 5 to 10 km thick.
The Earth – Part 1 (ART 7.1)
The crust is also the source of many of the
minerals and other substances that we use in
industry and other fields. The continental crust is
especially known for the wide variety of minerals
in its composition.
Tectonic Plates
by Jerry Coffey
The lithosphere is the rigid outermost shell of a
rocky planet. The lithosphere is broken up into
what are called tectonic plates. The Earth has eight
major and many minor plates. The lithospheric
plates ride on the asthenosphere. These plates
move in relation to one another at one of three
types of plate boundaries: convergent, or
collisional boundaries; divergent boundaries, also
called spreading centers; and transform
boundaries. Earthquakes, volcanoes, mountainbuilding, and oceanic trench formation occur
along plate boundaries. The lateral movement of
the plates is typically 50–100 mm annually.
The reason that tectonic plates are able to move is
the Earth‘s lithosphere has a higher strength and
lower density than the underlying asthenosphere.
Their movement is dictated by heat dissipation
from the Earth’s mantle. Lateral density variations
in the mantle result in convection, which is
transferred into tectonic plate motion through
some combination of frictional drag, downward
suction at the subduction zones, and variations in
topography and density of the crust that result in
differences in gravitational forces.
Tectonic plates consist of lithospheric mantle
overlain by one of two types of crust material:
oceanic crust (sima) and continental crust (sial).
Average oceanic lithosphere is typically 100 km
thick; its thickness is a function of its age: as time
passes, it conductively cools and becomes thicker.
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Because it is formed at mid-ocean ridges and
spreads outwards, its thickness is a function of its
distance from the mid-ocean ridge where it was
formed. For a typical distance oceanic lithosphere
must travel before being subducted, the thickness
varies…6 km thick at mid-ocean ridges to greater
than 100 km at subduction zones; for shorter or
longer distances, the subduction zone thickness
becomes smaller or larger, respectively. Typical
continental lithosphere is typically 200 km thick,
though this also varies considerably between
basins, mountain ranges, and stable cratonic
interiors of continents. The two types of crust also
differ in thickness, with continental crust being
considerably thicker than oceanic. The difference
being 35 km vs. 6 km.
The tectonic plates
have played a major
role in the formation
of the Earth as we
know it and will
continue to do so for
the entire existence of
this planet. At the
same time those
plates have wreaked
havoc on human
dwellings and
lifestyle by causing
earthquakes,
tsunamis, etc. Ah,
mother Earth is our
sustenance and our
bane.
The Earth – Part 1 (ART 7.1)
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