The document summarizes the formation of Earth from a cloud of dust and gas to the planet we know today. Billions of years ago, a disturbance in a giant cloud caused it to collapse and form a spinning disc that became the Sun and planets. Earth formed as matter collided and accumulated. Early Earth was molten, and oceans formed as it cooled over hundreds of millions of years. Asteroid impacts also contributed water and allowed life to evolve in the oceans over billions of years.

1. EVS
SEMESTER2

2. FORMATION OF EARTH
• Our planet began as part of a cloud of dust and gas. It has evolved
into our home, which has an abundance of rocky landscapes, an
atmosphere that supports life, and oceans filled with mysteries.

3. FORMATION OF EARTH
• Billions of years ago, Earth, along with the rest of our solar system, was entirely
unrecognizable, existing only as an enormous cloud of dust and gas. Eventually, a
mysterious occurrence—one that even the world’s foremost scientistshave yet
been unable to determine—createda disturbance in that dust cloud, setting forth
a string of events that would lead to the formation of life as we know it. One
common belief among scientistsis that a distant star collapsed, creating
a supernova explosion, which disrupted the dust cloud and caused it to pull
together. This formed a spinning disc of gas and dust, known as a solar nebula.
The faster the cloud spun, the more the dust and gas became concentrated at the
center, further fueling the speed of the nebula. Over time, the gravity at the
center of the cloud became so intense that hydrogen atoms began to move more
rapidly and violently. The hydrogen protons began fusing, forming helium and
releasing massive amounts of energy. This led to the formation of the star that is
the center point of our solar system—the sun—roughly 4.6 billion years ago.

4. FORMATION OF EARTH
• Planet Formation
The formation of the sun consumed more than 99 percent of the
matter in the nebula. The remaining material began to converge into
various masses. The cloud was still spinning, and clumps of matter
continued to collide with others. Eventually, some of those clusters of
matter grew large enough to maintain their own gravitational pull,
which shaped them into the planets and dwarf planets that make up
our solar system today.

5. FORMATION OF EARTH
• Planet Formation
Earth is one of the four inner, terrestrial planets in our solar system.
Just like the other inner planets—Mercury, Venus, and Mars—it is
relatively small and rocky. Early in the history of the solar system,
rocky material was the only substance that could exist so close to the
Sun and withstand its heat.

6. FORMATION OF EARTH
• Planet Formation
In Earth's Beginning
At its beginning, Earth was unrecognizable from its modern form. At first, it
was extremely hot, to the point that the planet likely consisted almost
entirely of molten magma. Over the course of a few hundred million years,
the planet began to cool and oceans of liquid water formed. Heavy
elements began sinking past the oceans and magma toward the center of
the planet. As this occurred, Earth became differentiatedinto layers, with
the outermost layer being a solid covering of relatively lighter material
while the denser, molten material sunk to the center.

7. FORMATION OF EARTH
• Planet Formation
Scientists believe that Earth, like the other inner planets, came to its
current state in three different stages. The first stage, described
above, is known as accretion, or the formation of a planet from the
existing particles within the solar system as they collided with each
other to form larger and larger bodies. Scientists believe the next
stage involved the collision of a protoplanet with a very
young planet Earth. This is thought to have occurred more than 4.5
billion years ago and may have resulted in the formation of Earth’s
moon. The final stage of development saw the bombardment of
the planet with asteroids.

8. FORMATION OF EARTH
• Planet Formation
Earth’s early atmosphere was most likely composed
of hydrogen and helium. As the planet changed, and the crust began
to form, volcanic eruptions occurred frequently.
These volcanoes pumped water vapor, ammonia, and carbon dioxide
into the atmosphere around Earth. Slowly, the oceans began to take
shape, and eventually, primitive life evolved in those oceans.

9. FORMATION OF EARTH
• Contributionsfrom Asteroids
Other events were occurring on our young planet at this time as well. It is
believed that during the early formation of Earth, asteroids were
continuously bombarding the planet, and could have been carrying with
them an important source of water.Scientists believe the asteroids that
slammed into Earth, the moon, and other inner planets contained a
significant amount of water in their minerals, needed for the creation of
life. It seems the asteroids, when they hit the surface of Earth at a great
speed, shattered,leaving behind fragments of rock. Some suggest that
nearly 30 percent of the water contained initially in the asteroids would
have remained in the fragmented sections of rock on Earth, even after
impact.

10. FORMATION OF EARTH
• Contributions from Asteroids
A few hundred million years after this process—around 2.2 billion to
2.7 billion years ago—photosynthesizing bacteria evolved. They
released oxygen into the atmosphere via photosynthesis and, in a few
hundred million years, were able to change the composition of
the atmosphere into what we have today. Our modern atmosphere is
comprised of 78 percent nitrogen and 21 percent oxygen, among
other gases, which enables it to support the many lives residing
within it.

11. STRUCTURE OF EARTH

12. STRUCTURE OF EARTH

13. FORMATION OF CONTINENTS
• The plate tectonic theory says that Earth’s surface is made up of slabs
of rock that are slowly shifting right under our feet.
• Because of this constant movement, today’s Earth looks a lot different
from what it did millions of years ago.
• In 1912, German scientist Alfred Wegener proposed that Earth’s
continents once formed a single, giant landmass, called Pangaea.
• In 1912, German scientist Alfred Wegener proposed that Earth’s
continents once formed a single, giant landmass, called Pangaea.

14. FORMATION OF CONTINENTS

15. FORMATION OF CONTINENTS
1 billionyears of tectonic platemovementin 40 seconds

16. FORMATION OF CONTINENTS
• Plate tectonics is a relatively new theory—in fact, it hadn’t become popular
until the 1960s. However, the concept of continental movement was
brewing long before it became widely accepted.
• In 1912,German scientistAlfred Wegener proposed a theory he called
continental drift. According to Wegener’s theory, Earth’s continents once
formed a single, giant landmass,which he called Pangaea.
• Over millions of years, Pangaea slowly broke apart, eventually forming the
continents as they are today. Wegener believed this continental drift
explained why the borders of South America and Africa looked like
matching puzzle pieces. He also pointed to similar rock formations and
fossils on these two continents as proof to back his theory.

17. CONTINENTAL DRIFT
HYPOTHESIS
• continental drift, large-scalehorizontal movements of continents relative
to one another and to the ocean basins during one or more episodes
of geologic time. This concept was an important precursor to the
development of the theory of plate tectonics, which incorporates it.
• The idea of a large-scale displacement of continents has a long history.
Noting the apparent fit of the bulge of eastern South America into the
bight of Africa, there are theories that the lands bordering the Atlantic
Ocean had once been joined. Some 50 years later, Antonio Snider
Pellegrini, a French scientist,argued that the presence of
identical Fossil plants in both North American and European coal deposits
could be explained if the two continents had formerly been connected, a
relationship otherwise difficult to account for. In 1908 Frank B Taylor. of
the United United States Invoked the notion of continental collision to
explain the formation of some of the world’s mountain ranges.

18. CONTINENTAL DRIFT
HYPOTHESIS

19. CONTINENTAL DRIFT
HYPOTHESIS

20. ISOTASY
• Isostasy (Greek isos "equal", stasis "standstill") or isostatic equilibrium is the
state of gravitational equilibrium between Earth’s crust or lithosphere
and mantle such that the crust "floats" at an elevation that depends on its
thickness and density. This concept is invoked to explain how different
topographic heights can exist at Earth's surface. Although originally defined in
terms of continental crust and mantle, it has subsequentlybeen interpreted in
terms of lithosphere and asthenosphere,particularly with respect to oceanic
island volcanoes, such as the Hawaaiin Islands.
• Although Earth is a dynamic system that responds to loads in many different
ways, isostasy describes the important limiting case in which crust and mantle are
in static equilibrium. Certain areas such as the Himalayas and other convergent
margins are not in isostatic equilibrium and are not well described by isostatic
models.
• The general term 'isostasy' was coined in 1882 by the American
geologist Clarence Dutton

21. ISOTASY

22. ISOTASY

23. PLATE TECTONICS
• Plate tectonics is a scientific theory that explains how major
landforms are created as a result of Earth’s subterranean movements.
The theory, which solidified in the 1960s, transformed the earth
sciences by explaining many phenomena, including mountain building
events, volcanoes, and earthquakes.

24. PLATE TECTONICS
• In plate tectonics, Earth’s outermost layer, or lithosphere—made up
of the crust and upper mantle—is broken into large rocky plates.
These plates lie on top of a partially molten layer of rock called
the asthenosphere. Due to the convection of
the asthenosphere and lithosphere, the plates move relative to each
other at different rates, from two to 15 centimeters (one to six
inches) per year. This interaction of tectonic plates is responsible for
many different geological formations such as the Himalaya mountain
range in Asia, the East African Rift, and the San Andreas Fault in
California, United States.

25. PLATE TECTONICS
• The idea that continents moved over time had been proposed before
the 20th century. However, a German scientist named Alfred
Wegener changed the scientific debate. Wegener published two
articles about a concept called continental drift in 1912. He suggested
that 200 million years ago, a supercontinent he called Pangaea began
to break into pieces, its parts moving away from one another. The
continents we see today are fragments of that supercontinent. To
support his theory, Wegener pointed to matching rock formations and
similar fossils in Brazil and West Africa. In addition, South America
and Africa looked like they could fit together like puzzle pieces.
•

26. PLATE TECTONICS
• Despite being dismissed at first, the theory gained steam in the 1950s
and 1960s as new data began to support the idea of continental drift.
Maps of the ocean floor showed a massive undersea mountain range
that almost circled the entire Earth. An American geologist named
Harry Hess proposed that these ridges were the result of molten rock
rising from the asthenosphere. As it came to the surface, the rock
cooled, making new crust and spreading the seafloor away from the
ridge in a conveyer-belt motion. Millions of years later, the crust
would disappear into ocean trenches at places
called subduction zones and cycle back into Earth. Magnetic data
from the ocean floor and the relatively young age of oceanic crust
supported Hess’s hypothesis of seafloor spreading.

27. PLATE TECTONICS
• There was one nagging question with the plate tectonics theory:
Most volcanoes are found above subduction zones, but some form far
away from these plate boundaries. How could this be explained? This
question was finally answered in 1963 by a Canadian geologist, John
Tuzo Wilson. He proposed that volcanic island chains, like the
Hawaiian Islands, are created by fixed “hot spots” in the mantle. At
those places, magma forces its way upward through the moving plate
of the sea floor. As the plate moves over the hot spot, one volcanic
island after another is formed. Wilson’s explanation gave further
support to plate tectonics. Today, the theory is almost universally
accepted.

28. PLATE TECTONICS VS
CONTINENTAL DRIFT
• The story begins with Alfred Wegener (1880–1930), a German meteorologist and
geophysicist who noticed something curious when he looked at a map of the
world. Wegener observed that the continentsof South America and Africa looked
like they would fit together remarkably well—take away the Atlantic Ocean and
these two massive landforms would lock neatly together. He also noted that
similar fossils were found on continentsseparated by oceans, additional evidence
that perhaps the landforms had once been joined. He hypothesized that all of the
modern-day continents had previously been clumped together in a
supercontinent he called Pangaea (from ancient Greek, meaning “all lands” or “all
the Earth”). Over millions of years, Wegener suggested,the continentshad
drifted apart. He did not know what drove this movement, however. Wegener
first presented his idea of continental drift in 1912, but it was widely ridiculed
and soon, mostly, forgotten. Wegener never lived to see his theory accepted—he
died at the age of 50 while on an expedition in Greenland.

29. PLATE TECTONICS VS
CONTINENTAL DRIFT
• Only decades later, in the 1960s, did the idea
of continental drift resurface. That’s when technologies adapted from
warfare made it possible to more thoroughly study Earth. Those
advances included seismometers used to monitor ground shaking
caused by nuclear testing and magnetometers to detect submarines.
With seismometers, researchers discovered that earthquakes tended
to occur in specific places rather than equally all over Earth. And
scientists studying the seafloor with magnetometers found evidence
of surprising magnetic variations near undersea ridges: alternating
stripes of rock recorded a flip-flopping of Earth’s magnetic field.

30. PLATE TECTONICS VS
CONTINENTAL DRIFT
• Together, these observations were consistent with a
new theory proposed by researchers who built on Wegener’s original
idea of continental drift—the theory of plate tectonics. According to
this theory, Earth’s crust is broken into roughly 20 sections called
tectonic plates on which the continents ride. When these plates press
together and then move suddenly, energy is released in the form of
earthquakes. That is why earthquakes do not occur everywhere on
Earth—they’re clustered around the boundaries of tectonic plates.

31. PLATE TECTONICS VS
CONTINENTAL DRIFT
• Plate tectonics also explains the stripes of rock on the seafloor with
alternating magnetic properties: As buoyant, molten rock rises up
from deep within Earth, it emerges from the space between
spreading tectonic plates and hardens, creating a ridge. Because
some minerals within rocks record the orientation of Earth’s magnetic
poles and this orientation flips every 100,000 years or so, rocks near
ocean ridges exhibit alternating magnetic stripes.

32. PLATE TECTONICS VS
CONTINENTAL DRIFT
• Plate tectonics explains why Earth’s continents are moving;
the theory of continental drift did not provide an explanation.
Therefore, the theory of plate tectonics is more complete. It has
gained widespread acceptance among scientists. This shift from
one theory to another is an example of the scientific process: As more
observations are made and measurements are collected, scientists
revise their theories to be more accurate and consistent with the
natural world.

33. PLATE TECTONICS VS
CONTINENTAL DRIFT
• By running computer simulations of how Earth’s tectonic plates are
moving, researchers can estimate where the planet's continents will
likely be in the future. Because tectonic plates move very slowly—
only a few centimeters per year, on average—it takes a long time to
observe changes. Scientists have found that the
planet’s continents will likely again be joined together in about 250
million years. Researchers have dubbed this
future continental configuration “Pangaea Proxima.”

34. PLATE TECTONICS VS
CONTINENTAL DRIFT
• One intriguing aspect of Pangaea Proxima is that it will likely contain a
new mountain range with some of the world’s highest mountains.
That is because as Africa continues to migrate north it will collide with
Europe, a collision that will probably create a Himalaya-scale
mountain range. However, Christopher Scotese, one of the scientists
who developed these simulations, cautions that it is difficult to
predict exactly how the continents will be arranged in millions of
years. “We don’t really know the future, obviously,” Scotese told
NASA. “All we can do is make predictions of how plate motions will
continue, what new things might happen, and where it will all end
up.”

35. PLATE TECTONICS VS
CONTINENTAL DRIFT