1.1.

The Universe
Earth is just one of the billions and billions of bodies in the universe. To appreciate how
special the Earth is, let us first explore the universe; the theories of how it began and
the origin of our own solar system.
Let's see what you already know. Answer Pre-test 1 now to test your knowledge. 
 
 LET'S EXPLORE
How and when did the universe begin? No other scientific question is more fundamental
or provokes such spirited debate among researchers. After all, no one was around
when the universe began, so who can say what really happened? The best that
scientists can do is work out the most foolproof theory, backed up by observations of
the universe. The trouble is, so far, no one has come up with an absolutely indisputable
explanation of how the cosmos came to be.
The Big Bang
Since the early part of the 1900s, one explanation of the origin and fate of the universe,
the Big Bang theory, has dominated the discussion. Proponents of the Big Bang
maintain that, between 13 billion and 15 billion years ago, all the matter and energy in
the known cosmos was crammed into a tiny, compact point. In fact, according to this
theory, matter and energy back then were the same thing, and it was impossible to
distinguish one from the other.
Adherents of the Big Bang believe that this small but incredibly dense point of primitive
matter/energy exploded. Within seconds the fireball ejected matter/energy at velocities
approaching the speed of light. At some later time—maybe seconds later, maybe years
later—energy and matter began to split apart and become separate entities. All of the
different elements in the universe today developed from what spewed out of this original
explosion.
Big Bang theorists claim that all of the galaxies, stars, and planets still retain the
explosive motion of the moment of creation and are moving away from each other at
great speed. This supposition came from an unusual finding about our neighboring
galaxies. In 1929 astronomer Edwin Hubble, working at the Mount Wilson Observatory
in California, announced that all of the galaxies he had observed were receding from us,
and from each other, at speeds of up to several thousand miles per second.
The Redshift
To clock the speeds of these galaxies, Hubble took advantage of the Doppler effect.
This phenomenon occurs when a source of waves, such as light or sound, is moving
with respect to an observer or listener. If the source of sound or light is moving toward
you, you perceive the waves as rising in frequency: sound becomes higher in pitch,
whereas light becomes shifted toward the blue end of the visible spectrum. If the source
is moving away from you, the waves drop in frequency: sound becomes lower in pitch,
and light tends to shift toward the red end of the spectrum. You may have noticed the
Doppler effect when you listen to an ambulance siren: the sound rises in pitch as the
vehicle approaches, and falls in pitch as the vehicle races away.
To examine the light from the galaxies, Hubble used a spectroscope, a device that
analyzes the different frequencies present in light. He discovered that the light from
galaxies far off in space was shifted down toward the red end of the spectrum. Where in
the sky each galaxy lay didn't matter—all were redshifted. Hubble explained this shift by
concluding that the galaxies were in motion, whizzing away from Earth. The greater the
redshift, Hubble assumed, the greater the galaxy's speed.
Some galaxies showed just a slight redshift. But light from others was shifted far past
red into the infrared, even down into microwaves. Fainter, more distant galaxies
seemed to have the greatest red shifts, meaning they were traveling fastest of all.
An Expanding Universe
So, if all the galaxies are moving away from Earth, does that mean Earth is at the center
of the universe? The very vortex of the Big Bang? At first glance, it would seem so. But
astrophysicists use a clever analogy to explain why it isn't. Imagine the universe as a
cake full of raisins sitting in an oven. As the cake is baked and rises, it expands. The
raisins inside begin to spread apart from each other. If you could select one raisin from
which to look at the others, you'd notice that they were all moving away from your
special raisin. It wouldn't matter which raisin you picked, because all the raisins are
getting farther apart from each other as the cake expands. What's more, the raisins
farthest away would be moving away the fastest, because there'd be more cake to
expand between your raisin and these distant ones.
That's how it is with the universe, say Big Bang theorists. Since the Big Bang explosion,
they reason, the universe has been expanding. Space itself is expanding, just as the
cake expanded between the raisins in their analogy. No matter whether you're looking
from Earth or from an alien planet billions of miles away, all other galaxies are moving
away from you as space expands. Galaxies farther from you move faster away from
you, because there's more space expanding between you and those galaxies. That's
how Big Bang theorists explain why light from the more distant galaxies is shifted farther
to the red end of the spectrum. In fact, most astronomers now use this rule, known as
Hubble's law, to measure the distance of an object from Earth—the bigger the redshift,
the more distant the object.
In 1965 two scientists made a blockbuster discovery that solidified the Big Bang theory.
Arno Penzias and Robert Wilson of Bell Telephone Laboratories detected faint
microwave radiation that came from all points of the sky. They and other physicists
theorized that they were seeing the afterglow from the Big Bang's explosion. Since the
Big Bang affected the entire universe at the same moment in time, the afterglow should
permeate the entire universe and could be detected no matter what direction you
looked. This afterglow is called the cosmic background radiation. Its wavelength and
uniformity fit nicely with other astronomers' mathematical calculations about the Big
Bang.
How Lumpy Do You Like Your Universe?
The Big Bang model is not uniformly accepted, however. One problem with the theory is
that it predicts a smooth universe. That is, the distribution of matter, on a large scale,
should be roughly the same wherever you look. No place in the universe should be
unduly lumpy.
But in 2001, astronomers announced the discovery of a group of galaxies and quasars
that fills more than 125 million million cubic light-years of space, and is presently the
largest structure in the universe. Instead of an even distribution of matter, the universe
seems to contain great empty spaces punctuated by densely packed streaks of matter.
Big Bang proponents maintain that their theory is not flawed. They argue that gravity
from huge, undetected objects in space (clouds of cold, dark matter we can't see with
telescopes, or so-called cosmic strings) attracts matter into clumps. Other astronomers,
still reluctant to believe in invisible objects just to solve an inexplicable problem,
continue to question fundamental aspects of the Big Bang theory.
In spite of its problems, the Big Bang is still considered by most astronomers to be the
best theory we have. As with any scientific hypothesis, however, more observation and
experimentation are needed to determine its credibility. Advances ranging from more-
sensitive telescopes to experiments in physics should add more fuel to the cosmological
debate during the coming decades.
The Steady State Theory
But the Big Bang is not the only proposed theory concerning our universe's origin. In the
1940s a competing hypothesis arose, called the Steady State theory. Some
astronomers turned to this idea simply because, at the time, there wasn't enough
information to test the Big Bang. British astrophysicist Fred Hoyle and others argued
that the universe was not only uniform in space—an idea called the cosmological
principle—but also unchanging in time, a concept called the perfect cosmological
principle. This theory didn't depend on a specific event like the Big Bang. Under the
Steady State theory, stars and galaxies may change, but on the whole the universe has
always looked the way it does now, and it always will.
The Big Bang predicts that as galaxies recede from one another, space becomes
progressively emptier. The Steady State theorists admit that the universe is expanding,
but predict that new matter continually comes to life in the spaces between the receding
galaxies. Astronomers propose that this new material is made up of atoms of hydrogen,
which slowly coalesce in open space to form new stars.
Naturally, continuous creation of matter from empty space has met with criticism. How
can you get something from nothing? The idea violates a fundamental law of physics:
the conservation of matter. According to this law, matter can neither be created nor
destroyed, but only converted into other forms of matter, or into energy. But skeptical
astronomers have found it hard to directly disprove the continuous creation of matter,
because the amount of matter formed under the Steady State theory is so very tiny:
about one atom every billion years for every several cubic feet of space.
The Steady State theory fails, however, in one important way. If matter is continuously
created everywhere, then the average age of stars in any section of the universe should
be the same. But astronomers have found that not to be true.
Astronomers can figure out how old a galaxy or star is by measuring its distance from
Earth. The farther away from Earth an object is, the longer it has taken light from the
object to travel across space and reach Earth. That means that the most distant objects
we can see are also the oldest.
The End of the Universe
Will the universe continue expanding? Will it just stop or even begin to contract? The
answer depends on the amount of mass that the universe contains. If the universe's
mass exceeds a certain crucial value, then gravity should eventually stop everything
from flying away from everything else.
With enough mass, the universe will eventually succumb to the overpowering force of
gravity and collapse again into a single point—a theory often called the Big Crunch. But
without enough mass, the universe will continue to expand. As of 2001, many scientists
concluded that the latter hypothesis appears to be the most likely.
In 1998, astronomers found an even more remarkable puzzle: the universe seems to be
accelerating while expanding, as if being pulled by some kind of "antigravity" force.
Other astronomers have since corroborated this finding using a variety of methods, and
have all but confirmed the existence of this mysterious "dark energy."
Source: https://www.scholastic.com/teachers/articles/teaching-content/origin-universe/  (
Links to an external site.)
 
 IMPORTANT DISCOVERY!
On May 20, 1964, American radio astronomers Robert Wilson and Arno Penzias
discovered the cosmic microwave background radiation (Links to an external
site.) (CMB), the ancient light that began saturating the universe 380,000 years after its
creation. And they did so pretty much by accident.
Bell Labs' Holmdale Horn Antenna in New Jersey picked up an odd buzzing sound that
came from all parts of the sky at all times. The noise puzzled Wilson and Penzias, who
did their best to eliminate all possible sources of interference, even removing some
pigeons that were nesting in the antenna. [CMB: Big Bang Relic Explained
(Infographic) (Links to an external site.)]
"When we first heard that inexplicable 'hum,' we didn’t understand its significance, and
we never dreamed it would be connected to the origins of the universe (Links to an
external site.)," Penzias said in a statement. "It wasn’t until we exhausted every possible
explanation for the sound's origin that we realized we had stumbled upon something
big."
And it was indeed big. Penzias and Wilson had spotted the CMB, the predicted thermal
echo of the universe's explosive birth. The landmark find put the Big Bang theory (Links
to an external site.) on solid ground, suggesting that the cosmos did indeed grow from a
tiny seed — a single point — about 13.8 billion years ago.
The two radio astronomers won the 1978 Nobel Prize in physics for their work, sharing
the award with Soviet scientist Pyotr Kapitsa.
Source: https://www.space.com/25945-cosmic-microwave-background-discovery-50th-anniversary.html#:~:text=On%20May
%2020%2C%201964%2C%20American,so%20pretty%20much%20by%20accident.  (Links to an external site.)

 
The cosmic microwave background (CMB) is thought to be leftover radiation from the
Big Bang, or the time when the universe began. As the theory goes, when the universe
was born it underwent a rapid inflation and expansion. (The universe is still expanding
today, and the expansion rate appears different depending on where you look  (Links to
an external site.)). The CMB represents the heat left over from the Big Bang.
You can't see the CMB with your naked eye, but it is everywhere in the universe. It is
invisible to humans because it is so cold, just 2.725 degrees above absolute zero
(minus 459.67 degrees Fahrenheit, or minus 273.15 degrees Celsius.) This means its
radiation is most visible in the microwave part of the electromagnetic spectrum.
Source: https://www.space.com/33892-cosmic-microwave-background.html  (Links to an
external site.)

1.2. The Evolution of Stars

When you look at the sky at night, what do you see? The seemingly countless brilliant
heavenly bodies that occupy the entire sky are our galaxies and stars. Have you ever
wondered how they came to be? 
___________________________________

Note: There are links on this page that will take you to a different webpage, outside of Canvas. You may
explore them to learn more!

__________________________________

LET'S EXPLORE!
Star formation
A star develops from a giant, slowly rotating cloud that is made up entirely or almost
entirely of hydrogen and helium. Due to its own gravitational pull, the cloud behind to
collapse inward, and as it shrinks, it spins more and more quickly, with the outer parts
becoming a disk while the innermost parts become a roughly spherical clump.
According to NASA, this collapsing material grows hotter and denser, forming a ball-
shaped protostar (Links to an external site.). When the heat and pressure in the
protostar reaches about 1.8 million degrees Fahrenheit (1 million degrees Celsius),
atomic nuclei that normally repel each other start fusing together, and the star ignites.
Nuclear fusion converts a small amount of the mass of these atoms into extraordinary
amounts of energy — for instance, 1 gram of mass converted entirely to energy would
be equal to an explosion of roughly 22,000 tons of TNT.
Evolution of stars

The life cycles of stars follow patterns based mostly on their initial mass. These include
intermediate-mass stars such as the sun, with half to eight times the mass of the sun,
high-mass stars that are more than eight solar masses, and low-mass stars a tenth to
half a solar mass in size. The greater a star's mass, the shorter its lifespan generally is.
Objects smaller than a tenth of a solar mass do not have enough gravitational pull to
ignite nuclear fusion — some might become failed stars known as brown dwarfs (Links
to an external site.).
 
Intermediate-mass stars
An intermediate-mass star begins with a cloud that takes about 100,000 years to
collapse into a protostar with a surface temperature of about 6,750 F (3,725 C). After
hydrogen fusion starts, the result is a T-Tauri star (Links to an external site.), a variable
star that fluctuates in brightness. This star continues to collapse for roughly 10 million
years until its expansion due to energy generated by nuclear fusion is balanced by its
contraction from gravity, after which point it becomes a main-sequence star (Links to an
external site.) that gets all its energy from hydrogen fusion in its core.
The greater the mass of such a star, the more quickly it will use its hydrogen fuel and
the shorter it stays on the main sequence. After all the hydrogen in the core is fused into
helium, the star changes rapidly — without nuclear radiation to resist it, gravity
immediately crushes matter down into the star's core, quickly heating the star. This
causes the star's outer layers to expand enormously and to cool and glow red as they
do so, rendering the star a red giant (Links to an external site.). Helium starts fusing
together in the core, and once the helium is gone, the core contracts and becomes
hotter, once more expanding the star but making it bluer and brighter than before,
blowing away its outermost layers. After the expanding shells of gas fade, the remaining
core is left, a white dwarf (Links to an external site.) that consists mostly of carbon and
oxygen with an initial temperature of roughly 180,000 degrees F (100,000 degrees C).
Since white dwarves have no fuel left for fusion, they grow cooler and cooler over
billions of years to become black dwarves (Links to an external site.) too faint to detect.
(Our sun should leave the main sequence in about 5 billion years.)
 
High-mass stars
A high-mass star forms and dies quickly. These stars form from protostars in just 10,000
to 100,000 years. While on the main sequence, they are hot and blue, some 1,000 to 1
million times as luminous as the sun and are roughly 10 times wider. When they leave
the main sequence, they become a bright red supergiant, and eventually become hot
enough to fuse carbon into heavier elements. After some 10,000 years of such fusion,
the result is an iron core roughly 3,800 miles wide (6,000 km), and since any more
fusion would consume energy instead of liberating it, the star is doomed, as its nuclear
radiation can no longer resist the force of gravity.
When a star reaches a mass of more than 1.4 solar masses, electron pressure cannot
support the core against further collapse, according to NASA. The result is a supernova.
Gravity causes the core to collapse, making the core temperature rise to nearly 18
billion degrees F (10 billion degrees C), breaking the iron down into neutrons and
neutrinos. In about one second, the core shrinks to about six miles (10 km) wide and
rebounds just like a rubber ball that has been squeezed, sending a shock wave through
the star that causes fusion to occur in the outlying layers. The star then explodes in a
so-called Type II supernova. If the remaining stellar core was less than roughly three
solar masses large, it becomes a neutron star (Links to an external site.) made up
nearly entirely of neutrons, and rotating neutron stars that beam out detectable radio
pulses are known as pulsars. If the stellar core was larger than about three solar
masses, no known force can support it against its own gravitational pull, and it collapses
to form a black hole (Links to an external site.).
 
Low-mass stars
A low-mass star uses hydrogen fuel so sluggishly that they can shine as main-sequence
stars for 100 billion to 1 trillion years — since the universe is only about 13.7 billion
years old (Links to an external site.), according to NASA, this means no low-mass star
has ever died. Still, astronomers calculate these stars, known as red dwarfs (Links to an
external site.), will never fuse anything but hydrogen, which means they will never
become red giants. Instead, they should eventually just cool to become white dwarfs
and then black dwarves.
Source: https://www.space.com/57-stars-formation-classification-and-constellations.html  
(Links to an external site.)
 

1.3. The Solar System

LET'S EXPLORE!
The planetary system we call home is located in an outer spiral arm of the Milky Way
galaxy.
Our solar system consists of our star, the Sun, and everything bound to it by gravity —
the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, dwarf
planets such as Pluto, dozens of moons and millions of asteroids, comets and
meteoroids.
Beyond our own solar system, there are more planets than stars in night sky. So far, we
have discovered thousands of planetary systems orbiting other stars in the Milky Way,
with more planets being found all the time. Most of the hundreds of billions of stars in
our galaxy are thought to have planets of their own, and the Milky Way is but one of
perhaps 100 billion galaxies in the universe.
While our planet a mere speck in the vast cosmos, we have a lot of company out there.
It seems that we live in a universe packed with planets — a web of countless stars
accompanied by families of objects, perhaps some with life of their own.
Size and Distance
Our solar system extends much farther than the eight planets that orbit the Sun. The
solar system also includes the Kuiper Belt that lies past Neptune's orbit. This is a
sparsely occupied ring of icy bodies, almost all smaller than the most popular Kuiper
Belt Object, dwarf planet Pluto.
And beyond the fringes of the Kuiper belt is the Oort Cloud. This giant spherical shell
surrounds our solar system. It has never been directly observed, but its existence is
predicted based on mathematical models and observations of comets that likely
originate there.
The Oort Cloud is made of icy pieces of space debris the sizes of mountains and
sometimes larger, orbiting our Sun as far as 1.6 light years away. This shell of material
is thick, extending from 5,000 astronomical units to 100,000 astronomical units. One
astronomical unit (or AU) is the distance from the Sun to Earth, or about 93 million miles
(150 million kilometers). The Oort Cloud is the boundary of the Sun's gravitational
influence, where orbiting objects can turn around and return closer to our Sun.
The Sun's heliosphere doesn't extend quite as far. The heliosphere is the bubble
created by the solar wind—a stream of electrically charged gas blowing outward from
the Sun in all directions. The boundary where the solar wind is abruptly slowed by
pressure from interstellar gases is called the termination shock. This edge occurs
between 80-100 astronomical units.

Formation
Our solar system formed about 4.5 billion years ago from a dense cloud of interstellar
gas and dust. The cloud collapsed, possibly due to the shockwave of a nearby
exploding star, called a supernova. When this dust cloud collapsed, it formed a solar
nebula—a spinning, swirling disk of material.
At the center, gravity pulled more and more material in. Eventually the pressure in the
core was so great that hydrogen atoms began to combine and form helium, releasing a
tremendous amount of energy. With that, our Sun was born, and it eventually amassed
more than 99 percent of the available matter.
Matter farther out in the disk was also clumping together. These clumps smashed into
one another, forming larger and larger objects. Some of them grew big enough for their
gravity to shape them into spheres, becoming planets, dwarf planets and large moons.
In other cases, planets did not form: the asteroid belt is made of bits and pieces of the
early solar system that could never quite come together into a planet. Other smaller
leftover pieces became asteroids, comets, meteoroids, and small, irregular moons.

Structure
The order and arrangement of the planets and other bodies in our solar system is due to
the way the solar system formed. Nearest the Sun, only rocky material could withstand
the heat when the solar system was young. For this reason, the first four planets—
Mercury, Venus, Earth and Mars—are terrestrial planets. They're small with solid, rocky
surfaces.
Meanwhile, materials we are used to seeing as ice, liquid or gas settled in the outer
regions of the young solar system. Gravity pulled these materials together, and that is
where we find gas giants Jupiter and Saturn and ice giants Uranus and Neptune

Potential for Life

Our solar system is the only place we know of that harbors life, but the farther we
explore the more we find potential for life in other places. Both Jupiter’s moon Europa
and Saturn’s moon Enceladus have global saltwater oceans under thick, icy shells.
Source: https://solarsystem.nasa.gov/solar-system/our-solar-system/in-
depth/#:~:text=Our%20solar%20system%20formed%20about,spinning%2C%20swirling
%20disk%20of%20material.

1.4. The Earth and its Moon

Finally! We have landed on Earth. We have discussed so far the theories about the
origin of the universe, the formation and evolution of stars, and the formation of our very
own solar system in the Milky Way Galaxy. Now we explore the history of our own
planet and its sole satellite, the moon. 
___________________________________

Note: There are links on this page that will take you to a different webpage, outside of Canvas. You may
explore them to learn more!

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 LET'S EXPLORE!
After the sun spun to light, the planets of the solar system began to form (Links to an
external site.). Although planets surround stars in the galaxy, how they form remains a
subject of debate. Despite the wealth of worlds in our own solar system, scientists still
aren't certain how planets are built. Currently, two theories are duking it out for the role
of champion. 
The first and most widely accepted theory, core accretion, works well with the formation
of the terrestrial planets like Earth (Links to an external site.) but has problems with
giant planets. The second, the disk instability method, may account for the creation of
these giant planets. 
Scientists are continuing to study planets in and out of the solar system in an effort to
better understand which of these methods is most accurate.

The core accretion model

Approximately 4.6 billion years ago, the solar system was a cloud of dust and gas
known as a solar nebula. Gravity collapsed the material in on itself as it began to spin,
forming the sun in the center of the nebula.
With the rise of the sun, the remaining material began to clump up (Links to an external
site.). Small particles drew together, bound by the force of gravity, into larger particles.
The solar wind swept away lighter elements, such as hydrogen and helium, from the
closer regions, leaving only heavy, rocky materials to create smaller terrestrial
worlds (Links to an external site.) like Earth. But farther away, the solar winds had less
impact on lighter elements, allowing them to coalesce into gas giants. In this
way, asteroids (Links to an external site.), comets (Links to an external site.), planets,
and moons were created.
Earth's rocky core (Links to an external site.) formed first, with heavy elements colliding
and binding together. Dense material sank to the center, while the lighter material
created the crust. The planet's magnetic field probably formed around this time. Gravity
captured some of the gases that made up the planet's early atmosphere. 
Early in its evolution, Earth suffered an impact by a large body that catapulted pieces of
the young planet's mantle into space. Gravity caused many of these pieces to draw
together and form the moon, which took up orbit around its creator.
The flow of the mantle beneath the crust causes plate tectonics, the movement of the
large plates of rock on the surface of the Earth. Collisions and friction gave rise to
mountains and volcanoes, which began to spew gases into the atmosphere (Links to an
external site.).
Although the population of comets and asteroids passing through the inner solar system
is sparse today, they were more abundant when the planets and sun were young.
Collisions from these icy bodies likely deposited much of the Earth's water on its
surface. Because the planet is in the Goldilocks zone, the region where liquid water
neither freezes nor evaporates (Links to an external site.) but can remain as a liquid, the
water remained at the surface, which many scientists think plays a key role in
the development of life (Links to an external site.).
Exoplanet observations seem to confirm core accretion as the dominant formation
process. Stars with more "metals" — a term astronomers use for elements other than
hydrogen and helium — in their cores have more giant planets than their metal-poor
cousins. According to NASA (Links to an external site.), core accretion suggests that
small, rocky worlds should be more common than the more massive gas giants.

The disk instability model

Although the core accretion model works fine for terrestrial planets, gas giants would
have needed to evolve rapidly to grab hold of the significant mass of lighter gases they
contain. But simulations have not been able to account for this rapid formation.
According to models, the process takes several million years, longer than the light
gases were available in the early solar system. At the same time, the core accretion
model faces a migration issue, as the baby planets are likely to spiral into the sun in a
short amount of time.
According to a relatively new theory, disk instability (Links to an external site.), clumps
of dust and gas are bound together early in the life of the solar system. Over time, these
clumps slowly compact into a giant planet. These planets can form faster than their core
accretion rivals, sometimes in as little as a thousand years, allowing them to trap the
rapidly-vanishing lighter gases. They also quickly reach an orbit-stabilizing mass that
keeps them from death-marching into the sun.
Source: https://www.space.com/19175-how-was-earth-formed.html  (Links to an external
site.)

The Moon
After the solar system was formed, it took another hundred million years for Earth's
moon to spring into existence. There are three theories as to how our planet's satellite
could have been created: the giant impact hypothesis, the co-formation theory and the
capture theory.

Giant impact hypothesis

The prevailing theory supported by the scientific community, the giant impact hypothesis
suggests that the moon formed when an object smashed into early Earth. Like the other
planets, Earth formed from the leftover cloud of dust and gas orbiting the young sun.
The early solar system was a violent place, and a number of bodies were created that
never made it to full planetary status. One of these could have crashed into Earth (Links
to an external site.) not long after the young planet was created.
Known as Theia, the Mars-sized body collided with Earth, throwing vaporized chunks of
the young planet's crust into space. Gravity bound the ejected particles together,
creating a moon that is the largest (Links to an external site.) in the solar system in
relation to its host planet. This sort of formation would explain why the moon is made up
predominantly of lighter elements, making it less dense than Earth — the material that
formed it came from the crust, while leaving the planet's rocky core untouched. As the
material drew together (Links to an external site.) around what was left of Theia's core, it
would have centered near Earth's ecliptic plane, the path the sun travels through the
sky, which is where the moon orbits today (Links to an external site.).
According to NASA (Links to an external site.), "When the young Earth and this rogue
body collided, the energy involved was 100 million times larger than the much later
event believed to have wiped out the dinosaurs."

Co-formation theory
Moons can also form at the same time as their parent planet. Under such an
explanation, gravity would have caused material in the early solar system to draw
together at the same time as gravity bound particles together to form Earth. Such a
moon would have a very similar composition to the planet, and would explain the
moon's present location. However, although Earth and the moon share much of the
same material, the moon is much less dense than our planet, which would likely not be
the case if both started with the same heavy elements at their core.

Capture theory
Perhaps Earth's gravity snagged a passing body, as happened with other moons (Links
to an external site.) in the solar system, such as the Martian moons of Phobos and
Deimos. Under the capture theory, a rocky body formed elsewhere in the solar system
could have been drawn into orbit around Earth. The capture theory would explain the
differences in the composition of Earth and its moon. However, such orbiters are often
oddly shaped, rather than being spherical bodies like the moon. Their paths don't tend
to line up with the ecliptic of their parent planet, also unlike the moon.
Although the co-formation theory and the capture theory both explain some elements of
the existence of the moon, they leave many questions unanswered. At present, the
giant impact hypothesis seems to cover many of these questions, making it the best
model to fit the scientific evidence for how the moon was created.
Source: https://www.space.com/19275-moon-formation.html
1.4. The Earth and its Moon

Finally! We have landed on Earth. We have discussed so far the theories about the
origin of the universe, the formation and evolution of stars, and the formation of our very
own solar system in the Milky Way Galaxy. Now we explore the history of our own
planet and its sole satellite, the moon. 
___________________________________

Note: There are links on this page that will take you to a different webpage, outside of Canvas. You may
explore them to learn more!

__________________________________

LET'S EXPLORE!
After the sun spun to light, the planets of the solar system began to form (Links to an
external site.). Although planets surround stars in the galaxy, how they form remains a
subject of debate. Despite the wealth of worlds in our own solar system, scientists still
aren't certain how planets are built. Currently, two theories are duking it out for the role
of champion. 
The first and most widely accepted theory, core accretion, works well with the formation
of the terrestrial planets like Earth (Links to an external site.) but has problems with
giant planets. The second, the disk instability method, may account for the creation of
these giant planets. 
Scientists are continuing to study planets in and out of the solar system in an effort to
better understand which of these methods is most accurate.

The core accretion model

Approximately 4.6 billion years ago, the solar system was a cloud of dust and gas
known as a solar nebula. Gravity collapsed the material in on itself as it began to spin,
forming the sun in the center of the nebula.
With the rise of the sun, the remaining material began to clump up (Links to an external
site.). Small particles drew together, bound by the force of gravity, into larger particles.
The solar wind swept away lighter elements, such as hydrogen and helium, from the
closer regions, leaving only heavy, rocky materials to create smaller terrestrial
worlds (Links to an external site.) like Earth. But farther away, the solar winds had less
impact on lighter elements, allowing them to coalesce into gas giants. In this
way, asteroids (Links to an external site.), comets (Links to an external site.), planets,
and moons were created.
Earth's rocky core (Links to an external site.) formed first, with heavy elements colliding
and binding together. Dense material sank to the center, while the lighter material
created the crust. The planet's magnetic field probably formed around this time. Gravity
captured some of the gases that made up the planet's early atmosphere. 
Early in its evolution, Earth suffered an impact by a large body that catapulted pieces of
the young planet's mantle into space. Gravity caused many of these pieces to draw
together and form the moon, which took up orbit around its creator.
The flow of the mantle beneath the crust causes plate tectonics, the movement of the
large plates of rock on the surface of the Earth. Collisions and friction gave rise to
mountains and volcanoes, which began to spew gases into the atmosphere (Links to an
external site.).
Although the population of comets and asteroids passing through the inner solar system
is sparse today, they were more abundant when the planets and sun were young.
Collisions from these icy bodies likely deposited much of the Earth's water on its
surface. Because the planet is in the Goldilocks zone, the region where liquid water
neither freezes nor evaporates (Links to an external site.) but can remain as a liquid, the
water remained at the surface, which many scientists think plays a key role in
the development of life (Links to an external site.).
Exoplanet observations seem to confirm core accretion as the dominant formation
process. Stars with more "metals" — a term astronomers use for elements other than
hydrogen and helium — in their cores have more giant planets than their metal-poor
cousins. According to NASA (Links to an external site.), core accretion suggests that
small, rocky worlds should be more common than the more massive gas giants.

The disk instability model

Although the core accretion model works fine for terrestrial planets, gas giants would
have needed to evolve rapidly to grab hold of the significant mass of lighter gases they
contain. But simulations have not been able to account for this rapid formation.
According to models, the process takes several million years, longer than the light
gases were available in the early solar system. At the same time, the core accretion
model faces a migration issue, as the baby planets are likely to spiral into the sun in a
short amount of time.
According to a relatively new theory, disk instability (Links to an external site.), clumps
of dust and gas are bound together early in the life of the solar system. Over time, these
clumps slowly compact into a giant planet. These planets can form faster than their core
accretion rivals, sometimes in as little as a thousand years, allowing them to trap the
rapidly-vanishing lighter gases. They also quickly reach an orbit-stabilizing mass that
keeps them from death-marching into the sun.
Source: https://www.space.com/19175-how-was-earth-formed.html  (Links to an external
site.)

The Moon
After the solar system was formed, it took another hundred million years for Earth's
moon to spring into existence. There are three theories as to how our planet's satellite
could have been created: the giant impact hypothesis, the co-formation theory and the
capture theory.

Giant impact hypothesis

The prevailing theory supported by the scientific community, the giant impact hypothesis
suggests that the moon formed when an object smashed into early Earth. Like the other
planets, Earth formed from the leftover cloud of dust and gas orbiting the young sun.
The early solar system was a violent place, and a number of bodies were created that
never made it to full planetary status. One of these could have crashed into Earth (Links
to an external site.) not long after the young planet was created.
Known as Theia, the Mars-sized body collided with Earth, throwing vaporized chunks of
the young planet's crust into space. Gravity bound the ejected particles together,
creating a moon that is the largest (Links to an external site.) in the solar system in
relation to its host planet. This sort of formation would explain why the moon is made up
predominantly of lighter elements, making it less dense than Earth — the material that
formed it came from the crust, while leaving the planet's rocky core untouched. As the
material drew together (Links to an external site.) around what was left of Theia's core, it
would have centered near Earth's ecliptic plane, the path the sun travels through the
sky, which is where the moon orbits today (Links to an external site.).
According to NASA (Links to an external site.), "When the young Earth and this rogue
body collided, the energy involved was 100 million times larger than the much later
event believed to have wiped out the dinosaurs."

Co-formation theory
Moons can also form at the same time as their parent planet. Under such an
explanation, gravity would have caused material in the early solar system to draw
together at the same time as gravity bound particles together to form Earth. Such a
moon would have a very similar composition to the planet, and would explain the
moon's present location. However, although Earth and the moon share much of the
same material, the moon is much less dense than our planet, which would likely not be
the case if both started with the same heavy elements at their core.

Capture theory
Perhaps Earth's gravity snagged a passing body, as happened with other moons (Links
to an external site.) in the solar system, such as the Martian moons of Phobos and
Deimos. Under the capture theory, a rocky body formed elsewhere in the solar system
could have been drawn into orbit around Earth. The capture theory would explain the
differences in the composition of Earth and its moon. However, such orbiters are often
oddly shaped, rather than being spherical bodies like the moon. Their paths don't tend
to line up with the ecliptic of their parent planet, also unlike the moon.
Although the co-formation theory and the capture theory both explain some elements of
the existence of the moon, they leave many questions unanswered. At present, the
giant impact hypothesis seems to cover many of these questions, making it the best
model to fit the scientific evidence for how the moon was created.
Source: https://www.space.com/19275-moon-formation.html  (Links to an external site.)

1.5. The Earth's subsystems

LET'S EXPLORE!
 
The Earth is considered as the living planet in the solar system. Life on earth needs
three main components in order to survive. These are the source of heat, presence of
liquid water and atmosphere. 
The sun is our source of heat. It provides the energy used for the production of
carbohydrates that sustain life. Water, as was mentioned before, is capable of
transforming between the different states of matter, e.g. solid, liquid and gas, but it was
the presence of liquid water that initially gave rise to single-cell organisms that later on
evolved into complex organisms. The presence of the atmosphere also ensures the
availability of gases that organisms need to thrive.  It also provided a barrier that
protects the earth's surface from the harmful rays of the sun, and to maintain our
surface temperature, a process known as greenhouse effect. 
The greenhouse effect on Earth. Some incoming sunlight is reflected by Earth's atmosphere and surface, but most is absorbed by
the surface, which is warmed. Infrared (IR) radiation is then emitted from the surface. Some IR radiation escapes to space, but
some is absorbed by the atmosphere's greenhouse gases (especially water vapour, carbon dioxide, and methane) and reradiated in
all directions, some to space and some back toward the surface, where it further warms the surface and the lower atmosphere. 
Source: Encyclopædia Britannica, Inc. https://www.britannica.com/science/greenhouse-effect (Links to an external site.)

The Subsystems 
Planet Earth is made up of four overlapping systems that contain all of world’s land
masses, water sources, living organisms, and gases. These four systems are known as
spheres. Three of these spheres are abiotic and one sphere is biotic. The spheres
interact with each other through the movement of energy and matter.
Geographers break down the Earth’s systems into four spheres that make up the
world’s air (atmosphere), water (hydrosphere), land (geosphere or lithosphere), and
living organisms (biosphere). In this breakdown, all of the Earth’s water is included in
the hydrosphere. This includes surface water (such as rivers, lakes, and oceans), water
in the ground, ice and snow, and water in the atmosphere in the form of water vapor.

Atmosphere
The Earth’s atmosphere is the gaseous layer that envelopes the world. This layer
mostly contains a mixture of mostly nitrogen (78%), Oxygen (21%), and argon (0.9%).
In addition, trace gases (carbon dioxide, nitrous oxides, methane, and ozone) account
for another tenth of a percent. Water vapor, dust particles, pollutants, and pollen also
can be found in mixed into the atmosphere.

Hydrosphere
All of the water on Earth is known collectively as the Earth’s hydrosphere. Water is
found in all three states on Earth. As water vapor in the atmosphere, as liquid in such as
in streams, rivers, lakes, ponds, and oceans, and as ice and snow.

Geosphere (Lithosphere)
The lithosphere contains the elements of the Earth crust and part of the upper mantle.
This is the hard and rigid outer layer of the Earth. The term is taken from the Greek
word lithos meaning “rocky”. This part of the Earth includes soil.

Biosphere
The biosphere covers all living organisms on Earth. There is an estimated 20 million to
100 millions different species in the world organized into 100 phyla that make up the five
kingdoms of life forms. These organisms can be found in almost all parts of the
geosphere. There are organisms in the air, soil, and water on Earth.
Source: https://www.geographyrealm.com/what-are-the-earths-systems/  (Links to an
external site.)
 

How do the subsystems interact with each

other?
Consider the picture below.
 

 Think of the many ways that the hydrosphere and the atmosphere connect. Evaporation
from the hydrosphere provides the medium for cloud and rain formation in the atmosphere.
The atmosphere brings back rainwater to the hydrosphere.
 In what way do the geosphere and hydrosphere connect? Water provides the moisture
and medium for weathering and erosion of rocks on in the geosphere. The geosphere, in
turn, provides the platform for ice melts and water bodies to flow back into the oceans.
 The atmosphere provides the geosphere with heat and energy needed for rock
breakdown and erosion. The geosphere, in turn, reflects the sun’s energy back into the
atmosphere.
 The biosphere receives gases, heat, and sunlight (energy) from the atmosphere. It
receives water from the hydrosphere and a living medium from the geosphere.

Source: https://eschooltoday.com/learn/interaction/ (Links to an external site.)

 

 ADDITIONAL READING
Another way to look at the interaction of the different subsystems is through
the biogeochemical cycles.  Read about the different biogeochemical cycles to
answer the following:

1. What are the common biogeochemical cycles?

2. Do you see the movement of energy and matter from one subsystem to another through
these cycles?
3. Is Earth a closed system? Why or why not?
4. Are humans considered to be part of the biosphere? Do you or do you not agree?
 
Here is your work:
1. Search a book or videos about "Did God Create the Universe?" by Stephen Hawking.
2. Make a reflection paper out of it, there should be an INTRODUCTION, BODY, and
CONCLUSION. A guide questions were given for the content of your paper. 
3.  At least 200 words.
Guide Questions:
1. How the Universe created based on what you've read or watched in the videos of
Stephen Hawking?
2. What are the concepts relating to the Origin of the Universe topic that used to explain
this matter?
3. How important to be open minded about the views of religious cosmology and
scientific explanation about the Origin of the Universe?