welcome to chapter two earth in space
from the good earth an introduction to
earth science and again I am your
instructor Dave Cocchiarella so today
we're talking about planetary science
the earth the word fits in the solar
system how it got there we're maybe
going we're going to talk about the old
ideas of how the earth into now in the
solar system the galaxy but the whole
universe and how those transformed into
the new ideas we're going to talk a
little bit about the origin of the
universe how we know how that happened
or how we know what we think happened
happened
the stars and the planets our own solar
system we're going to talk about the
earth and the earth sun system and why
that creates the seasons that will get
into the unique composition of the earth
the fact that we do have this atmosphere
the fact that we have water and three
states the fact that we have a magnetic
field around the earth that greatly
protects us from some very very
dangerous radiation all that to be found
here in Chapter to earth in space from
the good earth and introduction into her
science as you're likely aware at one
time it was believed the earth was the
center of not only well the solar system
of the University ancients didn't really
didn't see the solar system as a
separate thing or galaxies they just
thought . the earth is in the middle of
everything and so this was the the
picture you see on the left the
geocentric planetary system with the
earth at the middle and all the planets
revolving around the earth and you can
see the different signs that capricorns
well around the earth the Sun at the at
the outer edge they're going around the
earth and they believe the Stars the
Stars field was just a big sphere that
essentially revolved around the earth as
well and that was the geocentric concept
of the earth and from the geocentric
concept we went to the heliocentric
which puts the Sun at the center of the
solar system and then the solar system's
part of the galaxy and the universe as
well so the geocentric orbit hypothesis
ancient civilizations interpreted the
rising sun in the east and the settings
down the west to indicate that the Sun
and other planets all revolve around the
earth
really was a dominant idea for many many
many years more than 2,000 years while
many probably thought that this
geocentric notion was not correct and
something else must be going on very few
were willing to say that publicly of
course had to say that publicly was
close to heresy was against the
teachings of the church but the
heliocentric orbit hypothesis suggested
by Copernicus in the 16th century and
then confirmed by Galileo in the early
17th century through his observations
first the phases of Venus we saw Venus
going around us and Galileo was the
first one using a telescope which he
literally invented from a French toys
the French toy that was used to look at
pictures with two lenses and he took
those two lenses and create the
telescope he created the first telescope
and he looked at the the god that was
Venus and realize that much like their
the moon that means that different
phases and the changes in the size and
shape of Venus has observed from Earth
meant that it couldn't actually be in in
a rotation around the earth and that was
the first observation or data that
Galileo used to begin to develop the
hypothesis of a heliocentric system
Galileo used early telescopes that he
again invented to look out and observe
the changes in the size and shape of
Venus as it revolved around the Sun now
the two different illustrations
represent what it would look like in the
geocentric system with the earth being
at the center of the solar system in the
galaxy in the universe and Venus
actually revolving around the earth
while the Sun revolved around the earth
and if that were the case the geocentric
system then on the top of the
illustration you can see the six
different phases of Venus but what
Galileo actually saw was this other view
in which of course the sun is at the
center of the solar system venus
revolves around the Sun inside the orbit
of the earth and number for number three
on the right when the earth is
on one side and then you have the Sun
and then they penises on the other side
essentially the solar system you have
almost a full Venus as you see in three
and four but much smaller because it was
further away and then as it came around
the Sun we saw the happiness and the
Crescent Venus in the Crescent venis
being the largest because it was closest
to earth and this was the new
observation or the new data that allowed
them to change the theory of how the
solar system was that was set up the
geocentric to the heliocentric now once
it was realized and understood that the
earth was not the center of everything
and actually the son was the center of
our solar system it's sort of redefined
the paradigm of what existed and we
began to realize that we are in a solar
system that solar system was part of a
galaxy in that galaxy is part of the
universe and in fact ruthless just
simply a small rocky planet orbiting the
Sun which is a medium-sized star and
that son is one of billions of stars in
the Milky Way galaxy in the Milky Way
galaxy is actually just one of billions
of galaxies in the universe and based on
the rock record the earth is about 4.6
billion years old and based on the
theory the big bang theory it looks as
though the universe is somewhere in the
13 and a half to 14 billion year old
time frame
how do we know all that lots and lots of
different data that's come in at
different times all build together
coming in from different scientists at
different times to form one unifying
theory
in order for scientists to have the
hypothesis or the hypotheses to come up
with this unified theory they had to
have a lot of data a lot of observations
to get their ideas and their notions
from and the first bit of data that
scientists using these powerful
telescopes modern-day telescopes the
first observations they may was about
the size and the age of the universe now
the size can't be measured directly no
yardstick for that nor the age so they
use indirect measurements to estimate
the size and the age of the universe the
brightness and luminosity is stars give
the first clothes just how big the
universe was and how old it was as well
and also gave us an idea that the
universe was expanding now the
brightness and luminosity of stars that
help the to get an idea of some of the
distances between stars but the notion
that the universe was expanding I was
developed by looking at the Doppler
effect and doppler the capital T because
it's named after scientists Doppler who
came up with this idea and he was able
to look what we were able to use the
Doppler effect to look at the light
coming from stars and see that many of
the stars even most the stars were
actually moving away from us and so the
understanding of the Doppler effect and
how light from distant starts changes at
stars move provided more evidence to
sort of show us that the universe is
expanding and more evidence and more
observations in our attempt to
understand the universe and more
evidence and more observations to help
us come up with this unified theory of
the Big Bang so let's take a look at the
Doppler effect the apparent change in
the frequency of sound waves or light
waves due to the motion of a source
relative to an observer so the Doppler
effect had nothing to do with stars
Doppler notice that there was a change
in frequency of sound waves or light
waves or really any radiation due to the
motion of the source of that light or
sound or radiation relative to an
observer so an example a great example
is going to be the change in frequency
or the pitch of a siren from a passing
police car or and
ambulance as it comes towards you as one
frequency or pitch and as it moves away
from you and that changes and
essentially as the source of the sound
the police car on this case moves
towards you sound waves are scrunched
together they have a higher frequency or
higher pitch and as that police car
moves away from you
they're pulled apart and has a lower
frequency and that change in frequency
is the Doppler effect now the Doppler
effect was used with light from distant
stars and that as the stars are moving
away the the waves that light moved in
they were actually stretched the
radiation coming from the stars was
stretched and we can see that on the
electromagnetic spectrum the that the
shift in light coming from the stars
giving us our first indication that
stars and most objects that we see in
the heavens are moving away from not
only us but each other
indicating an expanding universe
this is how you can look at light from a
distant star and get the observation or
the indication of the data that star is
actually moving away light on earth is a
form of solar radiations the light from
the Sun is actually radiation and its
radiation that occurs at a very specific
wavelengths between 380 + 750 nanometers
a little anybody wavelength and that is
known as visible light now all stars
produce radiation and visible light at
these wavelengths so the radiation that
comes from the Sun is the same as a
radiation that comes from other stars
and the visible light that comes from
other stars also travels in this in this
range from 382 750 nanometers and you
can see the bottom of this illustration
that that that visible light that
radiation from 387 50 that is the the
more the colors of the rainbow from our
are violets to our purples and blues and
greens and yellows and oranges and reds
and that is the visible light now how we
see that white light from the Sun we are
not moving away from the Sun or Norway
moving closer to it so we see that as a
thick spectrum and due to the Doppler
effect the color of visible light from
distant stars
actually stretched again it's moving
away from us the wavelength is stretched
out toward the wavelengths at the red
end of the spectrum as the Stars move
away from Earth so astronomers use the
degree of redshift or how far that like
it stretched toward the red to determine
the distance to faraway galaxies and
faraway stars and estimate that most the
most distant galaxies in our universe
are at least 13 billion light-years from
Earth
what does that mean if the color of
light from other stars is shifted toward
the red end of the spectrum
well it tells us that other objects in
the universe and moving away from Earth
and actually also moving away from each
other
the further away the star the greater
the red shift in the faster the star is
actually moving away from us that what
we have also determined is not only our
stars moving away very quickly but the
further the star is away from us the
faster it's moving away from us and this
has given us the data to come up with a
hypothesis and ultimately the theory
that the universe must be expanding now
light from the most distant stars has
traveled more than 13 billion
light-years and we know that from the
the amount of the redshift that's
occurred so that is 13 billion years
time again one light-year is the
distance that light with the speed of
186,000 miles per second can travel in
one year so one light here is about 5940
billion miles and that tells us that
these most distant stars 13 billion
light-years away indicating to us that
um the the age of the universe a general
age of the universe between 13 and 14
billion year range one scientists had
this understanding that the universe is
expanding and everything is expanding
away from itself and they got the notion
of how far the most distant star is from
us that 13 billion light-years the
question was then well what if we
reverse that process
reversing the expansion of the universe
suggest that they actually the universe
began with an episode of very rapid
expansion from a much more compact form
and of course that's the notion of the
big bang that all space and time and
energy and mass are compact into a
single point and that the Big Bang was
an almost instantaneous period of rapid
expansion prior to that expansion there
was no space and time was all compact
down in that one . now as scientists
look at some of the evidence from the
big bang that they can find in our
sources and galaxies and throughout the
universe they began to understand that
within hours of the Big Bang simple
elements the simple elements of hydrogen
and helium formed has subatomic
particles began to combine the very
beginning there was no mass just the
subatomic particles as they began to
combine one proton and one electron
making hydrogen two protons two neutrons
and two electrons making helium as we
look at the universe now virtually most
of the universe is made up of hydrogen
and then to a lesser degree helium
virtually all of the mass of the
universe is hydrogen with a little bit
other parts of it being healing and then
how do we get all these other elements
that create everything around us where
that all can come from so hydrogen was
what was created during the original
formation of the universe after the Big
Bang a helium came from the fusing of
four hydrogen atoms all of the other
elements and all of the other complex
compounds are actually produced during
the life cycle of stars as we study
stars and we see what their life cycle
cycle is we begin to realize that stars
are simply fusion engines are fusion
reactors that fuse hydrogen together and
helium and then helium and more heavier
heavier and heavier elements so all the
other elements in the periodic table all
the other elements make up everything
that we see around us are basically
probably produced during the life cycle
of stars and some of the liner element
just in normal stars as they as they
burn brightly but most of the heavy
elements are actually created a drink
supernovas the gigantic explosions are
very large stars so just three elements
hydrogen oxygen carbon makeup about
ninety percent of the human body and
that's by wait five more elements
nitrogen calcium phosphorus potassium
sulfur make up about nine percent more
so it's very small amounts of many other
elements that are actually needed for
life so quite literally even the
elements that make up our entire bodies
were created during the life cycle of
stars so we are essentially all simply
composed of Stardust what is then the
lifecycle of a star we have to again
start at the beginning and after the Big
Bang there were clouds of gas and dust
being spread throughout what was the
growing universe and those regular
clouds of gas and dust created from the
big bang began to condense together to
form galaxies systems of stars stars and
galaxies in the small section of the
University you can see here in this
picture was taken from the Hubble Space
Telescope so you're looking at both
stars and both galaxies and this is just
the tiniest slice of space that those
Deep Space Telescope's they don't look
at space in a broad range just take a
little tiny spot and that's what we're
looking at so everything that we see out
there whether they're stars or galaxies
was pulled together from clouds of gas
and dust in the universe and we refer to
that process of creating stars as the
solar nebula theory the solar nebula
theory describes an ongoing process in
which gas and dust clump together to
form millions of stars and deform
individual stars as well so it's very
high temperatures and pressures in the
interior of stars that's where hydrogen
atoms are fused together to form helium
so if you look at this picture from the
than NASA space
telescope and that is actually a nebula
that is a cloud of dust and gas and as
that takes on greater and greater mass
that actually begins to exert the force
of gravity on objects around it
anything that has mass is its gravity
and the greater the mass the greater the
gravity so that's that's cloud gets
bigger it has more gravity pulling more
dust and eventually all that dust and
gas clump together at the center the
pressure and the heat from the gathering
of the gas and dust that's what creates
this heat that fuses hydrogen atoms
together to form helium and hydrogen
forms and helium just a little bit of
mass is lost and converted into energy
and that's the radiation we come from we
see coming from stars so stars burn
because they're fusing hydrogen into
helium and then they burn out when all
the hydrogen is used up our son like all
other stars will collapse when hydrogen
is completely used up initially it will
result in a temperature rise and an
expansion so as the Sun uses up all of
its hydrogen that is turning into helium
it will begin to fuse helium into
heavier elements well that will result
in more heat more heat means expansion
and our son in the next four to four and
a half billion years is expected to get
hotter and hotter and literally expand
out to the size of about the earth orbit
I'm higher temperatures would fuel more
of that fusion which converts helium
into carbon and that conversion of
helium into carbon just releases more
energy and more heat diffusion would end
when all the healing is used up carbon
it's a two bit of evil and Adam to be
forced back together in a son and so the
lots of heat of fusion would then allow
that star that's expanded out to Earth's
orbit to collapse in on itself so that
would be a white door if it still be hot
and eventually that whiteboard cool
white dwarf would cool into what's
called a black dwarf so the lifecycle of
our son started out as a clump of gas
and dust that through gravity got
denser and denser and denser until the
heat of the pressure and the friction
from the mass rubbing together was able
to fuse the first bit of hydrogen and
helium and the life cycle of a star the
size of our Sun about eighth-inning 8
billion years throughout that lifecycle
converting hydrogen and helium and then
when all the hydrogen is used up
beginning to convert helium into carbon
that being a hotter process causing the
Sun to expand expand expand then when
all the helium is used up and no more
fusion can occur because again carbon
too heavy to be fused together and then
it collapses on itself still hot so it's
a white dwarf and then as it cools
transitioning into a black dwarf when I
mentioned the size of our Sun that sort
of inferred that stars have different
sizes and in fact they have much much
variation in size we have giant stars we
have medium-size stars we have smaller
stars giant stars burns very brightly
and burnout much more quickly
medium-size stars may burn longer for
instance Giants stars are about 100 1000
times brighter than our Sun so they burn
out in about 10 to 20 million years
where intermediate-sized stars such as
the Sun they typically last summer
between eight and ten billion years so
this diagram we're looking at basically
shows different types of stars and also
I gives a luminosity of the star so how
luminous is it relative to our son with
some of those gigantic Delta and Rigel
being as much as ten top ten thousand
times brighter than our Sun then it also
gives the temperature in Kelvin of the
surface of the stars again those bigger
stars are much much hotter but it also
gives us an idea of how long those stars
will last now our son is on what's
called the main sequence right there in
the middle and it's a medium-sized
intermediate-sized star which again
should last about eight to 10 billion
years and what about four-and-a-half
billion years into that life cycle
intermediate size stars like our Sun do
not have the mass the pressure of the
heat to fuse elements together any
heavier than when the helium is fused
into carbon but larger giant stars they
do have the heat and the pressure and
the intensity to fuse heavier elements
and so giant stars collapse over
multiple stages hydrogen turns the
helium the helium forms carbon and it
gets much much bigger and then when they
finally begin to collapse the collapse
of those stars is enough pressure to
increase to form increasingly complex
elements so the carbon then forms oxygen
and so on and so on and so on so in the
ultimate collapse of a giant star that
is what is known as the supernova which
is the massive explosion and the
supernova is the one moment in time when
there's enough heat enough energy to
actually fuse all the heavier elements
that exist on the periodic table all the
heavier elements the silver the gold the
aluminum of the silicon magnesium
manganese whatever it is all of those
heavier elements our are fused from
those those elements of carbon and
oxygen and helium and hydrogen during
the supernova and not only the fuse
together to create those elements but
they're also scattered into space by
that explosion so those clouds of gas
and dust that was talking about that
with the beginning of the solar nebula
the solar nebula theory with those
clouds of gas and dust come from these
supernovas now the first clouds of gas
and dust came from the big bang but once
the first stars reform specifically the
first giant stars and the ongoing
process was stars formed hydrogen turns
helium the star turns itself on
radiation moves away from the store in
the form of light and heat it burns it
burns it burns when it finally collapses
and explodes the giant star it throws
out all those heavier elements into the
atmosphere and there's a great Kepler's
supernova and that was taken
the supernova ever expect to have
occurred on in 1604 but we're still
getting pictures of it at this time back
to the solar nebula theory when our
cloud of dust and gas finally begins to
fuse the first hydrogen into helium and
in the son is born those early sons
early stars are surrounded by the cosmic
debris that was that that cloud that
cloud of dust and gas and and as gravity
pulls it into the center or toward the
the center of the the star they begin to
rotate and so new stars are surrounded
by these rotating disk of cosmic debris
as that debris rotates around the new
star gravity and those larger clumps
again pulls debris and that sticks to
the club and the club gets bigger the
bigger club has more gravity that poor
pulls more stuff in and literally
through the process of accretion planets
form so gravity pulls debris together to
form planets that then revolve in a
consistent direction around the star so
all the planets only revolving it can
consistent direction if you look down
this on the Sun the top they all go
around counterclockwise they're all
essentially on the same plane now
they're not exactly on the same plane
and some get knocked off that plane by
with interactions from gravity or maybe
in collisions with other objects but
essentially they're all on a plane
called the plane of the ecliptic now
because gravity works as it does the
heavier stuff is pulled the center so
the heavier rockier planets are closer
to the star and the lighter gases
typically are further away from the star
and as we look at the formation within
the solar nebula theory of our solar
system we realize that many many many
potentially thousands or millions of
other solar systems exist very likely
have planets that revolve around those
stars as well so our solar system is
made up of our son
and the surrounding planets and the Sun
makes up about ninety nine point eight
percent of the total mass of the solar
system sun happens to be about a hundred
and fifty million kilometers or about 93
million miles 93 to 95 million miles
from Earth and and that is a one
astronomical unit that when we talk
about distances we use the distance
between the Earth and the Sun as one
unit because the distance is a large but
that's the distance from the Sun to the
earth about 93 million miles and what's
interesting about the Sun is it
undergoes differential rotation the
earth all rotates at the same speed as
its solid but the Sun is not so the
sun's equatorial region rotates about 25
days and the polar regions take about
thirty six days to rotate so this
results in some major disruptions of the
sun's magnetic field and that's where we
get the sunspots and the solar flares
that we see on the Sun like just about
everything else in nature of things run
in cycles and there's actually a cycle
to the frequency of sunspots at the
solar maximum we may see as many as a
hundred sunspots at a time and then at
the solar minimum we may see very few
sunspots and that difference between the
minimum and the maximum typically runs
about 11 years and sunspots and solar
flares can have an impact on the earth
as a throw energy in the form of the
solar wind toward the earth typically
are magnetic field deflects that energy
that solar wind but on these times very
very high high activity during the the
solar maximum it can disrupt some
communications and satellite
communications on earth
space weather and yes there is such a
thing as space weather is dominated by
the solar wind a constant stream of
charged particles emitted from the outer
layers of the sun's magnetic field the
solar wind affects a volume of space
known as the heliosphere so the
heliosphere is this massive had
basically globe around the Sun that
encompasses all the solar system and
well-well out beyond the solar system
with the solar wind actually it affects
space and the heliosphere is that region
of space in which our son is a dominant
influence heliosphere again extends far
beyond the solar system how Earth's own
magnetic field as you can see in this
particular illustration deflects the
solar wind around our planet helping to
protect our atmosphere without that
magnetic field our atmosphere will be
stripped away and that's what's happened
on other planets in the solar system
that do not have atmospheres it was a
stripped away by the solar wind in our
solar system the solar wind emanates out
for the Sun creating what's called the
heliosphere this massive global around
the Sun which goes that way out past the
outer reaches of our solar system and
the interactions of the solar when with
the Earth's magnetic field can also
generate beautiful visual effect the
aurora borealis the Northern Lights that
all happens in the upper atmosphere the
polar regions as the solar wind excites
and the molecules and the upper layers
of the atmosphere but occasional solar
eruptions can also disrupt the Earth's
magnetic field to produce electrical
blackouts satellites are in greater
danger from solar flares and then
features on the surface but it can
disrupt communications on earth because
of solar flares so the solar wind is a
dangerous thing in our magnetic field
definitely protects us from it
here's your standard illustration of the
solar system with our our son and of
course Mercury Venus Earth Mars those
the trustee of planets Jupiter Saturn
Uranus Neptune the jovian planets and
Pluto has the dwarf planet no longer
part of the nine now we just have the
eight and one of the reasons why Pluto
you can see not . on the plane of the
ecliptic it's a little bit
well it's quite a bit skewed from the
the planet the other planets are
rotating in you can also see between
Mars and Jupiter we got a bunch of
asteroids there that's the asteroid belt
and well beyond is the Kuiper belt for
that comment is coming from pretty
standard stuff you can see the
composition of Mercury Venus and Earth
and Mars very very similar with Korres
and the mantels and the crusts and the
composition of the jovian planets and
the gas giants Jupiter Saturn Uranus and
Neptune with a little itty bitty bit of
rock in the middle mostly a lot of a
water and ammonia and hydrogen liquid
hydrogen and different types of gases
here is more information on our a planet
Mercury Venus Earth Mars Jupiter Saturn
Uranus and Neptune the size the orbital
period the distance from the Sun high
and again we can see the different
atmospheric gases and . distance from
the Sun and millions of kilometers or an
au astronomical units where the earth is
one astronomical unit from the Sun and
then Jupiter's five and Uranus is 19 and
Neptune is literally 30 times the
distance from the Sun as the earth is
and and you can see almost a scale hear
the difference between the terrestrial
planets in the gas giants and with
Jupiter of course being the largest gas
giant but we always think of Saturn is
having rings but all of the gas giants
actually have rings around them again
the planets in our solar system divided
into two types classified into two types
I'll tell you many times during this
course that scientists the whole job is
to classify thing
well we're going to classify our planets
there's two classifications terrestrial
planets which are rocky and the jovian
planets which are mostly gas Mercury
Venus Earth and Mars those rocky
terrestrial planets close in heavier
elements being pulled close to the Sun
and the lighter elements of the gases
making up the jovian planets of Jupiter
Saturn Uranus and Neptune so what about
Pluto well as we said already about the
scientific method when more data new
observations come in we have to be able
to change our original theory so the
theories as to the structure of the
solar system having the nine planets
including Pluto had a change or began to
realize that Pluto wasn't really like a
lot of the other planets well like all
the other planets improved technology
rules resulted in recent discoveries
that there are several distant objects
that were basically similar in size or
even larger than Pluto that were
orbiting the Sun at that distance so the
international astronomical union group
of scientists got together and they
decided that they needed needed to do
something they either need to consider
the new objects as new planets because
again similar even larger than Pluto or
they needed to classify the new objects
including Pluto as a new group and they
decided to go with option two
so the IAU adopted a new definition for
the term planet a planet is an object
that orbits a star that's one orbits a
star and is massive enough 400
kilometres and radius or larger for
gravity to pull its material material
into an approx spherical shape so
gravity has to be strong enough to
overcome rigid body forces and bring the
material into a spherical shape and then
the last of the three criteria to be a
planet is a planet has to have swept its
entire neighborhood of any other debris
and its orbit so earth is swept up all
the nutrients orbit Jupiter has saturn
has mercury has but Pluto hasn't there's
other debris about the size of Pluto
even bigger in its orbit Pluto does not
meet the last part of the definite
action and was considered a founding
member of the new class of objects those
with dwarf planets Pluto is a dwarf
planet terrestrial planets then are
composed of rock and trust your planets
are divided into compositional layers as
these planets were forming the early
planets sometimes known as proto planets
just imagine a big rock moving around
the Sun and as it moves through its
orbit banks and other smaller rocks and
they stock stick together and the
Rockets bigger and bigger as it gets
bigger and bigger its gravity gets
larger begins to pull more and more
other bits of space debris and rock and
gas in and as it gets bigger and bigger
and bigger the gravity gets stronger
that gravity creates pressure and then
everything kind of banging into it and
the friction of the the gravity moving
things around creates heat and the
friction and heat begins to melt the
interior of the protoplanet has its
getting bigger and bigger and bigger and
we expect those early planets were
largely the same throughout homogeneous
just have the same material molten
throughout but as it got bigger and
bigger and gravity became stronger the
heavier elements like iron and nickel
got pulled the cores of these planets
these terrestrial planets and the
lighter elements migrated out to the
mantle under the cross like the helmets
of silicon and oxygen so terrestrial
planets are divided into compositional
rock layers based on the how heavy the
elements are with the heaviest elements
at the center now if we take a little
cutaway of the top of the mantle and we
see the crossbow the oceanic crust in
the continental crust we see the cross
lies on top of the mantle but the mantle
actually has two separate parts most of
the mantle just below the the
continental crust is this lower part
called and oceanic crust the
asthenosphere and the scene of spheres a
plastic layer in the upper mantle
meaning it's not quite moving
it's not quite solid imagine candle wax
that's not cold but just slightly warm
enough that maybe you can move shit just
a little bit that's the plastic layer of
this scene is fear
top of that as a rigid upper mantle
lithosphere with continental crust on
top of it and that that difference
between that's slightly plastic material
on that rigid material above it and that
is the natural process that allows for
seafloor spreading and continental drift
and this is going to explain the theory
of plate tectonics want to talk more
about that later on in the chapter are
in a class that is the jovian planets
are the large gas giants last four
planets in the solar system much of the
volume of these planets is made up in a
thick atmosphere that's on top of these
oceans of liquid gases that cover up the
much smaller rocky cores of the planets
and the jovian planets all have moons
lots of moons and they all also have
ring systems now we are really only see
the rings of Saturn but all the jovian
planets have rings and again they all
have these moons now we look at the four
largest moons of jupiter they play very
important role in the transition from
the geocentric to the heliocentric model
of the solar system as Galileo was
looking out and seeing the different
phases of Venus giving him the idea that
well maybe maybe it's step is rotating
maybe it's not a revolving around the
earth he also saw every night he could
see Jupiter as a bright spot but it can
also see much smaller little dots of
light around Jupiter which were in fact
these Jovian moons is four of Jupiter's
largest moons any realize that they were
there every night the same place at the
same time that they were not revolving
around there those moons were not moving
around the earth and if they weren't
moving around the earth maybe nothing
else was and that was a big part of the
transition from the the geocentric to
the heliocentric model of the solar
system
so let's talk about the earth and why
the earth is so special
the earth is so special because it has
water in three different form solid
liquid and gas and why is that because
it's just the perfect distance from the
Sun that it's warm enough to sustain
life but not so called that you can't
have liquid water so what makes this
planet so great this some unique things
happening with the planet and
specifically the Sun the earth
interaction between the two helping to
create the season so why is it hot at
the equator than at the the north pole
while its North Pole's further north
it's cold up north why is that the
absolute answer is because the
equatorial regions receive more solar
radiation then the polar regions and we
just first look at this this
illustration at the equator where the
noonday Sun is directly overhead
straight overhead the Sun comes in and
the same amount of sunlight warms a much
much smaller section of the earth as
does what's happening and then polar
regions meaning at the same time the
same day the same little ray of sunlight
has to come in and warm a much much
larger section of the northern latitude
so the further north you are the less
amount of sunlight each little spot on
the earth receives because at the
equatorial region they receive more of
that solar radiation known as insulation
incoming solar radiation then the
equator is going to be warm the amount
of solar radiation reaching the Earth's
surface depends on the angle the sun's
rays strike the earth had a much greater
angle up around 90 degrees more heat is
delivered by insulation with the Sun is
directly overhead as sunlight is
distributed over a smaller area the
total annual insulation is the smallest
at the polls and the greatest at the
equator so you can see by the
illustration solar energy is diluted
over a larger area when the sunlight
strikes at a low angle such a high add
latitudes
it's not diluted it's over a much
smaller area when it strikes at a high
angle over the southern latitudes
seasonal temperature contrast are due to
the amount of insulation incoming solar
radiation reaching the earth seasonal
differences and insulation are due to
the tilt of the earth axis and the angle
of the sun rays so the tilt of the earth
is 23 and a half degrees the earth is
tilted on an imaginary axis or into 23
and a half degrees to vertical so the
tropic of cancer which is that line
there to the north the tropic of
capricorn to the south
those are lines are 23 and a half
degrees north and south of the equator
and as the Sun moves when the earth
moves around the Sun that tilt of the
axis always points in the same direction
so at one point and the earth journey
around the Sun the earth is tilted
toward the Sun the northern hemisphere
is tilted toward the Sun at the same
time the southern hemisphere is tilted
away when the northern hemisphere is
tilted toward the Sun that's the
northern hemisphere summer in the
southern hemisphere at the same time is
tilted away
it's the southern hemisphere winter you
can see from the illustration that no
matter where the earth is in its trip
around the Sun and the axis is always
pointed to the same spot in space so
upper right-hand corner wintertime
december twenty first winter solstice
the northern hemisphere is pointed away
from the Sun so the northern hemisphere
is going into winter opposite side of
the illustration summer soul sister on
jun 21st in Northern Hemisphere's
pointed toward the Sun because the
northern hemisphere is pointed toward
the Sun the Rays of the Sun or more
direct and provide more heat to the
northern hemisphere and therefore here
in summertime at the equinoxes both
September and march that access to still
. the same spot but you're basically on
the side of the sons of the entire
hemisphere is getting equal parts of day
and night and those are the beginning of
spring and beginning a fall equal parts
a day night
why they call them equinox the Sun is
directly overhead at different places
during different times of the year going
to different seasons during summer in
the Northern Hemisphere the Sun is
directly overhead the tropic of cancer
that northern line during the winter in
the Northern Hemisphere the Sun is
directly overhead of the tropic of
capricorn in the southern hemisphere
during spring and fall the equinox is
now in the northern hemisphere the Sun
is directly overhead the equator so the
Earth's axis is always tilted in the
same direction that causes the
distribution of solar radiation to
change with the season that's ultimately
the reason why we have the seasons that
change and the amount of the
distribution of solar radiation due to
the Earth's tilted axis so it is the
tilt of the access that causes the
different seasons because the tilt of
the axis in our winter time the Northern
Hemisphere's . away from the Sun and our
summertime the northern hemisphere is
pointed toward the Sun it is not the
distance from the Sun that causes the
seasons this is a common misconception
it's not the distance from the Sun as a
matter of fact we look at the slightly
elliptical orbit around the Sun it's
almost a circle which is slightly
elliptical were about a hundred and
fifty-two million kilometers in the
summertime and about a hundred and forty
17 kilometers in the winter so actually
closer to the Sun during what's known as
our Perry helium perihelion is when the
celestial object is closest to the
objects orbiting the app helium in July
is when we are farthest from the Sun and
that's actually our warm season or
farther away so it is not the distance
from the Sun that creates the seasons
the tilt of the axis also causes us to
have longer days in the summertime and
the amount of sunlight during any given
day is known as the photo . so a longer
photo . in the summertime then in the
wintertime and the best way to see that
is let's look at the top illustration
and look at the northern hemisphere when
you see the tropic of cancer that is the
black line going through North Africa
there that Center black line is the
equator to the south is the tropic of
capricorn but the Tropic of Cancer the
black line moving through the northern
Africa you can see that it has a much
longer distance to travel if you take it
from that point all the way to the edge
of the globe then the tropic of
capricorn that moves from the the east
side of south africa is a much shorter
distance so that northern latitude has a
longer day than that southern latitude
and that is because again the tilt of
the earth so with latitude higher
latitudes have more daylight and low
latitudes and summer and then it's the
opposite and winner so it's always the
case you have longer days in the
summertime when you do and the
wintertime and that also helps to make
it warmer and the summer
again as a terrestrial and rocky planet
Earth has a fairly unique composition as
well the interior can be divided into
three major compositional layers the
crust the lighter elements of silicon
oxygen the mantle composed of rocks made
up of three killed key elements oxygen
silicon and magnesium and the core
mainly iron and nickel but what's most
important about the core is the inner
core is solid and the partially melted
outer core kind of moves around that
solid and it's that difference between
the solid inner core and the partially
melted how to record that creates the
Earth's magnetic field and it's very
important that magnetic field is what
protects our atmosphere from the solar
wind also as we've already discussed in
addition to the three major competition
layers of the earth the core of the
mantle and the crust scientists
recognize two layers with different
properties near the surface that look
this fear the rigid outer layer composed
the crossed an upper mantle and has seen
this fear the plastic slowly flowing
layer and the upper most part of the
mantle the lithosphere is literally
divided into large slabs known as
tectonic plates again this is the theory
of plate tectonics plates move over the
earth surface to produce earthquakes and
volcanoes mountain belts and various
features on the seafloor in this
illustration shows us the many many
different interactions of the oceanic
crust and the continental crust
I am what's happening in this Cena
sphere in the lithosphere and we're
going to talk in great detail about this
when we talk about plate tectonics and
that theory of continental drift
another unique property of the earth is
the geothermal gradient earth's
temperature increases with depth the
average temperature rises about 25
degrees Celsius for every kilometer that
you go down in the ground now heat is
generated by well the formation of the
planets all the terrestrial planets
cooled following formation only large
planets like the earth actually still
retain that heat plus there's
radioactive decay of elements occurring
in the Earth's interior that also relate
releases heat and so the earth has this
geothermal gradient where it gets hotter
as you get deeper so what makes earth
that actually shares many many features
and other planets special we have liquid
water mostly momentum of the other
planets out frozen water or are some
level of liquid gases we have liquid
water we have gravity and a protective
atmosphere we have life-sustaining gases
and a strong magnetic field because we
have a solid core with a liquid outer
core around it so there's a lot of great
unique properties of Earth that allow it
to sustain life liquid water of course
essential for life on Earth and is
maintained by that appropriate
temperature range between 0 and 100
degrees Celsius
venus is too close to the Sun originally
all the water evaporated in the
atmosphere and there's water vapor
molecules split by ultraviolet radiation
and hydrogen are essentially loss into
space Mars too cold today to have liquid
water there's some frozen water there
but that liquid water is one of the
things that makes earth so unique
earth-sized is sufficient to Bruce
enough gravity so we're big enough to
create enough gravity to hold a nice
thick atmosphere of gas in place over
the earth and that atmosphere so
important because it protects us from
incoming asteroids and comets and that
doesn't happen every day when I'm not
big ones anyway but it also protects us
from the harmful solar radiation x-rays
and ultraviolet light so that atmosphere
it's very very important to us we know
that Earth is unique in that it's
biospheres actually alter the
composition of the atmosphere
how is that well in the beginning earth
was the atmosphere is mainly the line
nitrous lot of methane lot of co2 it
wasn't until there was the first
blue-green algae plants that took carbon
dioxide in and release oxygen so there's
a very long . and the Earth's history
known as the rise of oxygen where carbon
dioxide was taken in by plants and
oxygen was released by plants now very
important because carbon dioxide is a
potent greenhouse gas for instance on
Venus where higher carbon dioxide
content exists
temperatures are about 464 degrees
celsius so the lack of carbon dioxide
and the oxygen has been a big benefit to
the earth all created by the biosphere
the composition of the Earth's
atmosphere is just right absorb enough
heat to keep average temperatures at
about 59 degrees Fahrenheit so when you
take the globe the entire globe all
times all places the average
temperatures about 59 degrees Fahrenheit
without greenhouse gases so part of the
Earth's atmosphere not only oxygen but
are these other greenhouse gases like
water vapor and carbon dioxide and
methane without those greenhouse gases
the average temperature would actually
be 0 degrees Fahrenheit well below
freezing so if you look at the left and
the right illustrations
this gives you an idea why the incoming
solar radiation from the Sun is a very
short wave and that incoming shortwave
radiation passes through the atmosphere
its absorbed by the earth and the earth
heats up and then the earth emits
long-wave radiation in the form of
infrared or heat if there was no
atmosphere like you see on the left side
the short wave incoming solar radiation
would come through the app would come
through strike the earth warm the earth
and that all that heat from the earth
just escaped into space with a
protective atmosphere the incoming
shortwave radiation passes through the
atmosphere the atmosphere does not
absorb the shortwave radiation shortwave
radiation heats up the earth the earth
re radiates it radiates way its infrared
energy some of it does go out the space
but much of it is absorbed by the
atmosphere warming the atmosphere and
keeping that constant temperature at
about 59 degrees Fahrenheit so that
thick atmosphere it's just perfect keep
the earth at just that perfect
temperature 59 degrees Fahrenheit
insulation or the incoming solar
radiation which is a shorter wavelengths
largely passes through the atmosphere to
be absorbed by the Earth's surface the
infrared IR radiation heat that we feel
that is a longer wavelength is emitted
by the earth it tries to locate escape
to space but part of it is absorbed by
the greenhouse gases due to it being a
longer wavelength and that's what keeps
the earth Warner so the greenhouse
effect is very important it's just a
runaway greenhouse effect that could
cause global warming
alright lastly the Earth's magnetic
field protects Earth from harmful
solarwinds that would strip away the
atmosphere because of that magnetic
field through the molten rocks in the
outer core and the relatively rapid
planetary motion that we get this
magnetic field smaller planets are
slowly rotating planets have lost heat
and therefore they have a very weak
magnetic field because we have this very
rapid rotation and this molten rock in
the outer core we have a strong magnetic
field and that magnetic field literally
protect the Earth from the solar wind
that would typically strip away our
atmosphere so again the earth is very
unique
it's life-sustaining liquid water and
just the perfect temperature we're going
to talk about some other parts of the
solar system that actually create a
threat for the earth asteroids and
comets and near-earth objects coming up
in chapter 3
