These power point presentations accompany the
readings in the text.
In some cases additional material will expand on
the text.
In other cases, the power points will emphasize
what is most important in the text.
Comments on “The Earth as a Habitable Planet”
p. 2-3 in text.
Be familiar with the terms in bold lettering.
Also remember this number: 71% of the Earth’s
surface is covered by oceans.
A few comments on Fig. 1.1 in the text:
Countless geological, physical, chemical,
biological, and atmospheric interactions are
taking place on and within the Earth.
The following figure divides the Earth into five
systems or spheres. The arrows represent the
interactions among the spheres.
p. 3
The interactions can be illustrated with a few examples.
In the geosphere, the Earth’s internal heat causes
volcanoes and hydrothermal vents which release lava,
steam, and carbon dioxide.
The steam adds water to the ocean and atmosphere.
The carbon dioxide dissolves into the ocean or enters
the atmosphere.
The internal heat causes the mantle to convect thereby
producing seafloor spreading and continental drift.
Chemical interactions between the lava and seawater
change the chemistry of both the lava and seawater.
Through photosynthesis, plants use the energy of
sunlight to extract carbon from carbon dioxide and
incorporate it into the biosphere.
Through respiration and bacterial decay of dead plants
and animals, the carbon dioxide and water are cycled
back into the oceans and atmosphere.
The energy of sunlight evaporates water and adds
water vapor to the atmosphere.
Water vapor condenses into rain and snow which fall on
the land to chemically weather the soil and rocks,
physically erode the land, and take the dissolved
chemicals and sediment to the ocean via rivers.
Chemical and detrital sediments deposited on the ocean
floor and the water soaking the sediments are carried
down subduction zones to be incorporated into the
interior of the Earth, heated by the Earth’s internal heat,
and released back into the hydrosphere and atmosphere
via volcanic and hydrothermal activity.
Growing glaciers extract water from the atmosphere and
hydrosphere and add mass to the crust causing it to
subside.
Melting glaciers add water to the atmosphere,
hydrosphere and biosphere, and their disappearance
unloads the crust and causes it to isostatically rebound.
Here are two examples of heat engines.
Heat energy is being converted into mechanical energy.
The interactions among the spheres are being driven by
two heat engines.
One heat engine is driven by the Earth’s internal heat
that has been produced by the radioactive decay of
isotopes and by the original accretion and density
stratification of the Earth.
The heat is exiting the interior by conduction (the
transfer of heat from atom to atom) and convection (the
mass currents in the mantle and core).
The external heat engine is driven by the radiation from
the sun.
Comments on “History of the Earth” p42-43.
These are some of the basic things about the early
history of the Earth, I want you to know:
*The Sun, Earth and other planets of the solar system
formed as the gases, dust, ice and rocky material in
space accumulated because of the force of gravity.
This is called accretion.
*This happened about 4.56 billion years ago (a good
number to know).
*The Earth heated up because the accretion of
material under gravity produces heat and because of
the heat of naturally radioactive isotopes that was
included in all that accreted material.
*The Earth became molten and density stratified.
That’s a fancy term meaning the heaviest materials
sank to the center of the Earth and the lightest, like the
steam and gases erupted from many volcanoes,
formed the early atmosphere.
*The early atmosphere was mostly N2, H2O, CO2, and
HCl – the common volcanic gases.
*The oceans formed when the Earth cooled enough
that steam could condense into water.
*The water was acidic because of the CO2 and HCl
dissolved in it.
*This caused chemical weathering of crustal rocks
which released many ions into seawater.
*In addition the volcanoes released excess volatiles
into seawater.
*Ions from chemical weathering and volcanic
eruptions dissolved in seawater made it salty.
Some comments on
Fig. 2.2.
This is a complicated
diagram, but these are
the things I want you
to know (see next
page).
*The Earth formed about 4.6 million years ago.
*The early environment was oxygen-free (called anoxic).
*The first life, anaerobic bacteria, evolved before 3.5 billion years
ago.
*The roughly 3.5 billion years the first photosynthetic bacteria
(cyanobacteria) evolved. They were the first to produce free
oxygen.
*These first organisms were marine, not terrestrial.
*Over time the free oxygen increased in the ocean and
atmosphere.
*The first multicellular organisms evolved.
*The “Cambrian explosion” occurred around 543 million
years ago. This was a rapid, significant increase in the
number of organisms with shells, possibly related to the
increase of oxygen in the environment.
*Based on the fossil record, the first land organisms
appeared shortly after this.
*Life didn’t always keep advancing steadily. At times there
were mass extinction events.
*We will be covering ocean biology later in the
session, at which time we will cover the other
biological terms mentioned in this section
Now to discuss Fig. 2.10
in your text.
The following slides
describe what I would
like you to take away
from this figure.
The underlined terms
are important to
remember.
*Density stratified means that the layers (strata is
the Latin term for layer) are arranged according
to density with the lightest material on top and
the heaviest material at the center of the Earth.
*The atmosphere is the lightest and is above
everything else. The oceans which are the next
lightest, form an incomplete layer below the
atmosphere.
*The lithosphere is the
rigid shell of the Earth.
The upper part of the
lithosphere, the part we
walk on, is called the
crust. The boundary
between the crust and
the rest of the mantle is
called the Moho.
*The lithosphere is not one piece, but it is broken into
plates that move relative to each other. The continents
are parts of these plates and so they move around also;
this is called continental drift.
* These plates are moved, to a first approximation,
by convection currents in the mantle.
*The mantle is immediately
below the lithosphere and
is not completely rigid, but
over geologic time can flow
slowly in giant convection
currents somewhat like the
convection currents in this beaker of molten wax.
The mantle is heated on the bottom by the very hot
core. The temperature difference between the hot
bottom of the mantle and the cooler top of the mantle
drives the convection.
*The core is at the
Earth’s center; it is the
densest and hottest part
of the Earth. It is divided
into a liquid outer core
and a solid inner core.
*In general temperature,
density and pressure
increase from the Earth’s
surface to its center.
*The crust consists of the continents and ocean basins. While we can see many kinds of
rocks on the continents, the average composition of the continents is granitic. Granite is
a silicate igneous rock comparatively rich in the elements aluminum, potassium and
sodium. Under the sediments the ocean basins are mostly made of the silicate volcanic
rock called basalt. Basalt is comparatively rich in iron, magnesium, and calcium. Basalt is
darker and denser than granite.
*The mantle is consists of other types of silicate materials, not granite or basalt.
*The core is much different. It is mostly iron with essentially no oxygen or silicon. It is
the densest part of the Earth.
Now to say a little about the chemistry of these layers:
*The lithosphere with its crust, and the mantle are
made of silicate materials for the most part. Most (but
not all) of the rocks you see walking around on the
Earth’s surface are silicate materials.
*Silicate materials are made up mostly of two elements:
oxygen (O) and silicon (Si). All the other elements make
up smaller proportions of natural silicate materials. Since
most of the rocks you see are silicates, the adjective
“rocky” roughly means silicate for us.
*The crust consists of the
continents and ocean basins.
While we can see many kinds
of rocks on the continents,
the average composition of
the continents is granitic.
Granite is a silicate igneous
rock comparatively rich in
the elements aluminum,
potassium and sodium. Under the sediments the ocean
basins are mostly made of the silicate volcanic rock called
basalt. Basalt is comparatively rich in iron, magnesium,
and calcium. Basalt is darker and denser than granite.
Here are some pictures of
granite:
and
basalt:
 Now don’t get overwhelmed by all the density and depth
numbers mentioned in Fig. 2.10, you don’t have to learn them.
 One thing to note is that below the crust the rest of the
lithosphere has a chemical composition more like the mantle,
so that in chemical terms the lower lithosphere is lumped in
with the mantle. Whereas when considering physical
properties, such as rigid vs. soft and flowing, the lithosphere is
separated from the mantle. A little confusing, but the
following two figures in color better illustrate this than the
gray-shaded Fig. 2.10.
 Please note that the lower mantle (mesosphere) is labeled
rigid. That is not really true, it can still flow though not as
quickly as the upper mantle (asthenosphere).
Layering of the Earth
Upper Layers of the Earth (note that the flowing
ashenosphere is just below the lithosphere).