Transcript Diapositiva 1 - ZANICHELLI.it

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Earth and
its rocks
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Earth’s structure
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The surface of the Earth
The surface of planet Earth is made up of the ocean
floors and continental masses.
On the ocean floors there are ridges, volcanic mountain
ranges, and trenches, the lowest points of the Earth’s
crust.
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Endogenous and
exogenous processes
Endogenous processes occur inside Earth and
generate the ocean floors and continents.
Exogenous processes are determined by the actions
of the atmosphere, hydrosphere and biosphere, and
they shape what is produced by the endogenous
dynamic.
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The inner structure of Earth /1
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The inner structure of Earth /2
Earth is made of layers, from the surface to the nucleus
we can find:
• the crust;
• the mantle;
• the core.
The thin and rigid lithosphere (crust + upper mantle)
rests on the fluid asthenosphere (lower mantle).
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Earth’s magnetic field
The outer core generates
the planet’s bipolar
magnetic field which
extends beyond the
surface of the Earth and
protects it from solar
winds.
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Earth’s internal energy
The engine of endogenous processes is Earth’s internal
thermal energy, which is partly derived from the heat of
accretion of our planet and partly derived from radioactive
substances in Earth’s crust and mantle.
Convective cells of the asthenosphere transfer this heat
to the upper parts.
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Lithosphere and tectonic plates
The lithosphere is divided into tectonic plates which are
dragged over the asthenosphere by convective movements.
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The lithosphere is dynamic
Tectonic plates move
and grow near ridges
where the oceanic
lithosphere is shaped
and are then destroyed
in oceanic trenches.
Endogenous processes
occur along plate
boundaries.
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Igneous and metamorphic rocks
Endogenous processes
create magma, which
solidifies at depth (magma)
or appears on Earth’s
surface (lava). The
solidification of magma and
lava creates igneous rocks.
The transformation of preexisting rocks gives rise to
metamorphic rocks.
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The exogenous
dynamic
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Exogenous agents shape the
landscape
Exogenous agents, like air, water, wind and living beings,
cause the weathering and erosion of rocks, but also
transportation and sedimentation of debris.
The exogenous dynamic is activated by solar heat that warms
up the Earth, in a non-uniform way depending on the time of
year and geographic location.
The effects of this dynamic triggered by the Sun are different
and also depend on: climate, geography and exogenous
agents.
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Sedimentary rocks
Sedimentary rocks arise from the cementation of erosion
debris which are transported and deposited elsewhere by
exogenous agents.
They are nearly always stratified and may contain fossils.
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The soil
Soil is the most external and
thinnest layer of Earth’s crust
and is made up of solid,
liquid and gaseous
substances.
It is formed by a process
called «pedogenesis», which
occurs over a long period of
time with degradation of
parental material by
atmospheric agents.
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The history of
Earth and life
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The depth of geological time
Geological time is measured on two different scales:
• the relative geologic time scale reconstructs the sequence
of geological and biological events without dates;
• the absolute geological time scale dates geological events
in millions and billions of years (for example, Pangea is dated
back to 250 millions years ago).
Relative dating is based on the sequence of sedimentary layers
and the fossils they contain.
Index fossils allow temporal correlations to be made between
different areas; the facies fossils help retrace paleoclimate and
paleogeography.
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The geochronographic scale /1
Geochronologic unit
Eon
Duration (millions of years)
2000
Era
Period
Epoch
Age
0.01
The geochronographic scale consists of 4 eons, called
Hadean, Archean, Proterozoic and Phanerozoic, divided into
eras, periods, epochs and ages.
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The geochronographic scale /2
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