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SOLAR SYSTEM
FORMATION
ORIGIN OF THE EARTH
SOLAR SYSTEM
PLANETESIMALS
PLANETESIMALS
COLLIDE
MAGMA OCEAN
Along with the other planets of the solar system, the early
Earth was formed from the initial nebula materials.
Specifically, from the gas and dust that formed the flat
disc revolving around the nucleus of condensation that
led to the Sun formation. The particles of this disc started
to join and merge. These aggregates collided with each
other adding its matter and forming larger bodies called
planetesimals. These planetesimals, in turn, also collided
with each other and formed the planets of the solar system
in a process called “accretion”.
As planetesimals collided, they joined and merged due to the enormous amount of heat that was
generated in each impact. The result was a very hot early Earth covered by a magma ocean, up to 1000
km depth, which allowed differentiation into layers (core, mantle and crust).
EARTH DIFFERENTIATION INTO LAYERS
The rock mass that was formed, the “protoearth”, was so hot
that it melted. It was possible due to the heat generated by the
continuous impact of rock fragments, by the gravitational
contraction and by the heat released by radioactive decay of
some chemical elements. As a result there was a
reorganization of the entire planet materials and earth
materials were arranging in order of density:
Melted iron was heavier and sank toward the center to form the nucleus or core of the planet.
The rocky material formed the outer layers of the Earth. Of these, the lightest rock materials rose to the
surface and formed the crust, while thicker materials remain in the intermediate layers and formed the
mantle.
ORIGIN OF THE PRIMITIVE ATMOSPHERE
Magma and volcanic activity simultaneously
released a large amount of gases (magma
degassing process) which were trapped by
Earth's gravity and formed a first layer of gas
around the geosphere. The result was the first
primitive atmosphere, whose composition was
very different from today's atmosphere: There
was no oxygen and it was very rich in water
vapour and CO2. It also contained other gases
such as H2, N2, methane (CH4), ammonia (NH3)
and lesser amounts of others (CO, SO2, H2S,
etc.)
PRIMITIVE CRUST
(very thin, with
frequent volcanic
activity
ORIGIN OF THE OCEANS
As planetesimals were running out, the impacts ceased and
the early Earth began to cool slowly. First fragments of
mainland were formed, and the crust, which at first was very
thin, was gradually becoming thicker as material into Earth
were getting cooler.
In the atmosphere, large clouds began to form by
condensation of the huge amount of water vapour that
was contained within. As it continued cooling, the clouds
came down and began to produce rain, this rain cooled still
more Earth's surface, generating more rain. And it rained and
rained, we do not know for sure how many years, until the
clouds broke up and the sun came out, but now over the
newly formed oceans.
4500 ma
ago:Earth
formation
LAYERS OF THE EARTH
The Earth has an average radius of 6,373 km. There
are two models or divisions of the Earth into layers
according to the criteria used:
1) COMPOSITIONAL MODEL, based on the chemical
composition of the materials of the layers, divided into
crust, mantle and core
2) MECHANICAL MODEL, based on the behavior of
the layers, divided into lithosphere, asthenosphere,
mesosphere and endosphere (outer and inner core).
LAYERS OF THE EARTH
CONTINENTAL AND OCEAN CRUST
CONTINENTAL CRUST
The crust is the most superficial
and the thinnest layer of rock on
Earth (if we compare the Earth with
an egg, the crust would have the
thickness of the shell). Its average
thickness varies between 5-10 km in
the oceans and about 33 km on the
continents, but it increases
considerably its thickness below
mountain ranges (the higher altitude
they are, the deeper "roots" beneath
the continent are there). The
thicknesses has been measured of
over 80 km beneath the Himalayas.
Therefore, there are two types of
crust, continental and oceanic
crust, with the following distinctive
features:
OCEANIC CRUST
THICKNESS
GROSS, variable (33 - 80 Km below ranges)
THIN, almost constant (5 -10 Km)
COMPOSITION
Mainly granitic
Basaltic rock (cooled lava)
DENSITY
Low density (2,7 g/m3)
Denser (3,0 g/m3)
MAXIMUM AGE
There are very old areas, almost of 4000
m.y. old
ALLWAYS YOUNG, maximum 180
m.y. old
Continental self and slope
- Continental crust comprise the continents, that is the mainland and its extension beneath the sea to
reach the ocean floor. In the continental edge we can differentiate two areas: the continental shelf, a
shallow area (up to 200m) with low inclination which can be more or less extensive depending on area;
Further is the continental slope, a steep slope that leads to the ocean floor.
- Oceanic crust covers the deep sea floor, which depth is about 3,000 m on average.
THE MANTLE
The mantle is the middle layer of Earth, comes to 2,900 km
depth and its temperature is between 1000 °C and 3700 °C.
Although its chemical composition is homogeneous (a
rock called peridotite), its physical condition varies greatly
with depth, so we distinguish several areas:
The uppermost mantle is glued to the crust and both
together forms a rigid structural unit about 100-300 km
thick (depending areas) called lithosphere. It’s a mixed
layer, and may be continental or ocean lithosphere
depending on the crust type that contains. This lithosphere
is rigid and forms the tectonic plates
Below the lithosphere, peridotite rock is in a semisolid state, with
some plasticity (ability to move). This region was called
asthenosphere, but currently this designation is in disuse. This area
corresponds to the rest of the upper mantle and reaches 670 km
depth
Below is located the lower mantle, with
denser peridotite due to pressure.
In the core-mantle boundary is a layer
about 200 km thick called D’’- layer. From
here melted material rises as plumes that
can reach the surface.
THE CORE AND THE EARTH’S MAGNETIC FIELD
The core extends from 2900 km depth to the center of the Earth.
It is a very dense layer and it is at a very high temperature
and pressure. It consists mainly of iron, but also contains
nickel and other elements such as oxygen, sulfur and silicon.
There are two different zones: the outer core, which is fluid
and where the materials are stirred in strong convection currents
and the inner core, which is solid (due to the greater
pressure).
Earth's magnetic field arises due to the movement of the masses of molten iron in the outer core,
which generate electrical currents around the mass of solid iron of the inner core. Altogether the Earth's core
behaves like a giant electromagnet, in a process known as dynamo effect.
The Earth behaves like a magnet whose north and south
magnetic pole do not match with the geographical and also
their position changes over time. Currently, the north
magnetic pole lies about 1,800 km away from the geographical
pole and it is moving through the northern part of Canada to
Alaska.
It should be noted, that when we talk about Earth's magnetic
poles, we call north magnetic pole to the one which is near the
geographic north pole and we call south magnetic pole to the
one which is near the geographic south pole, however their
actual magnetism is opposite to that which is indicated by their
names, at least at present, because the Earth's magnetic
field polarity is reversed many times throughout the
history of the Earth, without a pattern or a reason known by
now.
On Earth, like in any magnet, the field lines go from the
magnetic north pole to the magnetic south pole
The Earth's magnetic field creates a space, the
magnetosphere, which is spherical towards the Sun
and elongated in the opposite direction. It extends to
about 60,000 km from Earth in the Sun direction and
much farther in the opposite direction. The
magnetosphere acts as a shield that deflects most
of the solar wind (ions and free electrons emitted by
the Sun). If it didn’t exist, atmospheric gases would
be dragged away making life impossible on Earth.
In the magnetic poles, where the Earth's magnetic field lines sink in, electrically charged particles from the
solar wind enter and collide with atoms and molecules of the upper layers of the atmosphere, producing a
luminous phenomenon known as the Northern and Southern Lights or auroras. It also can cause
communications interferences.
Auroras occur when on the surface of the sun takes place
a solar storm, which we can recognize by the well-known
sunspot areas. These solar storms are tremendous
explosions, with flashes of hundreds of thousands of
kilometers in length (stronger than the simultaneous
explosion of 1,000 atomic bombs). They release into
space large amounts of electrically charged particles
called solar wind.
The Sun has a cyclical activity, so that every 11 years
or so reaches a maximum of sunspots. The year 2013
was one of those maximum of solar activity, in which
some of the solar storms were so intense that it was
necessary to lock some satellites or turn them off to
prevent any damage.
Twin auroras have been
observed, simultaneously
in both poles. However,
detect both auroras has
been very laborious
because they only are
visible during the night and
there are very few days a
year in which there are
"night" at both poles at
once.