Transcript Our Solar System and Earth

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OUR SOLAR SYSTEM
& EARTH
HOW AND WHY DO THEORIES BECOME
GENERALLY ACCEPTED?
UNIT 4
OUR SOLAR SYSTEM & EARTH
CONTENTS
UNIT 4 BASICS
3 Unit 4 Overview
4 Unit 4 Learning Outcomes
5 Unit 4 Lessons
6 Unit 4 Key Concepts
LOOKING BACK
8 What Happened in Unit 3?
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KEY CONTENT
10 Threshold 4—Earth & the Solar System
11 Threshold 4: Earth & the Solar System
13 How Did Earth and the Solar System Form?
14 The Sun
15 How Our Solar System Formed
16 What Was the Young Earth Like?
17 The Early Atmosphere
18 Our Shifting Globe
19 Why We’re All Lava Surfers
20 Introduction to Geology
21 Alfred Wegener & Harry Hess
22 Eratosthenes
23 Introduction to the Geological Time Chart
24 Principles of Geology
LOOKING AHEAD
26 What’s Next in Unit 5?
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UNIT 4
OVERVIEW
Key Disciplines:
Physics, chemistry, and geology
Timespan:
The Sun and Solar System formed about 4.5 billion years ago
Driving Question:
How and why do theories become generally accepted?
Threshold for this Unit:
Threshold 4: Earth & the Solar System
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UNIT 4
LEARNING OUTCOMES
By the end of Unit 4, students should be able to:
1.
Explain why planets are more complex than stars.
2.
Use evidence to explain how the Earth and its atmosphere developed and changed over time.
3.
Explain the basic mechanisms and key pieces of evidence for plate tectonics, and how plate
tectonics impacts life on Earth.
4.
Define geology, the types of questions geologists ask, and the tools they use to answer those
questions.
5.
Explain why geology is important to understanding the history of the Earth.
6.
7.
Understand how geologists can work with scientists and historians from other
disciplines to form a deeper understanding of the history of the Earth.
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UNIT 4
LESSONS
4.0 Earth and the Formation of Our Solar System
The debris left over from the formation of the Sun experienced many collisions as it began to orbit
the newly formed Sun. These collisions led to the formation of the Earth and the other planets in
Solar System through a process called accretion.
4.1 What Was the Young Earth Like?
As giant hunks of rock, metal, and ice slammed into the Earth’s surface, it became a planet with
three layers. Despite its violent and unstable beginning, Earth slowly became the world we know
today, and the interplay between the layers resulted in the Earth as we know it.
4.2 Why Is Plate Tectonics Important?
Once rock formed on the early Earth, large masses of rock called plates began to appear. As a
result of the movement of these plates, towering mountains and trembling earthquakes resulted.
The surface of our Earth is constantly in motion, and plate tectonics is responsible for the shape
and position of the Earth’s landforms.
4.3 Ways of Knowing: Our Solar System and Earth
The history of our planet is written in the rock record, along with clues about the future of the Earth
as well. Rock detectives—geologists—study these clues and often observe Earth’s changes first
hand.
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Continued next slide
UNIT 4
KEY CONCEPTS
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accretion
Archaean eon
asteroid
atmosphere
circadian rhythm
continental drift
convergent plate boundaries
core (of the Earth)
crust (of the Earth)
differentiation (chemical)
divergent plate boundaries
Earth
exoplanet
gas giant
geology
greenhouse effect
Hadean eon
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light spectrum
mantle (of the Earth)
orbit
ozone
Pangaea
planet
planetesimal
plate tectonics
protoplanetary disk
rocky planets (or terrestrial planets)
seafloor spreading
Solar System
subduction zones
Sun
tectonic plates
transform plate boundaries
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LOOKING BACK
WHAT HAPPENED
IN UNIT 3?
Unit 3 focused on the formation and lifecycle of stars, as well as the emergence of new
chemical elements. We learned:
• How stars formed.
• About the life (and death) of a star.
• About the origin of heavy chemical elements in aging and dying stars.
• How views of chemical elements changed over time.
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KEY CONTENT
THRESHOLD 4—EARTH &
THE SOLAR SYSTEM
Video
• Large clouds of dust and gas were created in the aftermath of the death of stars. These
chemically complex areas seeded the development of new generations of stars.
• The very first stars were made entirely of hydrogen and helium because those were the only
elements that made up the clouds that these stars formed out of. Once a few generations of
stars had lived and died, star death had created a greater variety of chemical elements, so these
clouds were much more diverse.
• Planets formed from the small amount of material from these clouds that did not become part of
the new star. The complex cloud of chemicals formed by the death of later stars enabled much
greater complexity than hydrogen and helium alone.
• The Earth and solar system formed about 4.5 billion years ago when the universe was already
over 8 billion years old, and many generations of stars had lived and died.
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HOW DID EARTH AND THE
SOLAR SYSTEM FORM?
Video Talk / David Christian
• When our Sun formed out of a cloud of gas, it used over 99 percent of the matter in that cloud.
• The leftover matter orbited the Sun. Collisions, gravity, and the rotation of the matter around the
Sun caused it to clump together.
• Earth and the other planets in our Solar System formed as a result.
• Because of the way matter was distributed, the planets that formed closest to the Sun (including
Earth and Mars) are rocky.
• Planets further from the Sun are gaseous.
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THE SUN
Video
• Before the Sun formed, our Solar System consisted of a massive gas cloud one light-year
across, with a mass equal to that of the Sun.
• The formation of our Solar System probably commenced when the explosion of a nearby star
sent a shock wave through the gas cloud, causing the cloud to start spinning. As it spun, gravity
pulled the matter in the cloud more closely together, causing the cloud to spin faster and
collapse.
• The Sun finally lit up once the pressure and temperature had built up enough in the in the core of
the forming star. The temperature needed for hydrogen to fuse into helium is around 10 million
degrees Kelvin.
• About 99.9 percent of all of the mass contained in the original gas cloud went into making the
Sun. The planets were formed from the small amount of materials that were spinning around the
Sun and did not become part of it.
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HOW OUR SOLAR SYSTEM
FORMED
Article / Cynthia Stokes Brown
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Planet formation is driven by accretion, a process by which larger objects grow even larger by
using gravity to attract smaller, nearby objects to them.
• There are two types of planets in the Solar System: rocky and gas. The rocky planets are closest
to the Sun, and they are composed mainly of rocks and metals. The gas planets are further from
the Sun and are composed mainly of gas and ice.
• Not all rocky planets are the same. All of the rocky planets were very hot when they formed but
cooled over time. Mercury and Mars cooled so much that they became solid. Venus may not be
completely solid. The Earth did not completely solidify. Some parts of the Earth are solidified
(crust and inner core) and others are not (outer core and mantle).
• Scientists currently believe that the Moon formed before the Earth had finished forming the
layers it has today. This process began when a large object collided with the young Earth. The
Moon formed from some of the material that was ejected into space after this collision and was
captured in an orbit around the Earth by the Earth’s gravitational attraction.
• The Moon has a huge impact on life on Earth. First, the collision that resulted in the formation of
the Moon gave the Earth its tilt, which is responsible for the seasons we experience. Although
the Moon is smaller than the Earth, its gravitational attraction on the Earth can be seen in the
tides. The Moon’s gravitational attraction also helps reduce the Earth’s wobble and slow its spin.
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WHAT WAS THE YOUNG
EARTH LIKE?
Main Talk / David Christian
• The earliest period of Earth’s history is called the Hadean eon. Hades was the god of the
underworld in Greek mythology, and this name was chosen to represent the “hellish” nature of
the early Earth.
• The young Earth was very hot, its air was filled with dangerous gases, there was radioactivity,
and there were many asteroid strikes.
• Over time, the Earth went through a process called differentiation. The heaviest materials in the
Earth, particularly metals, sank to the center of the Earth to form its core.
• Above this layer, there formed a rocky sludge called the mantle.
• The thin, outer surface of the Earth became its crust.
• The gases and moisture that escaped from Earth formed our atmosphere.
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THE EARLY ATMOSPHERE
Video
• The Hadean eon, the most violent early period of Earth’s history, was characterized by high
temperatures, collisions, and the process of differentiation.
• Perhaps the most important of these collisions was when a large, Mars-sized object struck the
Earth, leading to the formation of the Moon.
• The Archaean eon saw the development of a diversity of oceans, seas, rivers, and beaches.
This is also when the first life forms emerged.
• Some of those early life forms released oxygen during photosynthesis. The resulting buildup of
oxygen in the atmosphere had a tremendous impact on life.
• The Phanerozoic eon, the Earth’s current eon, has seen a proliferation of plant and animal life.
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OUR SHIFTING GLOBE
Video Talk / David Shimabukuro
• The surface of the Earth is in constant motion. This motion is very slow—about the speed a
human fingernail grows! —but over really long periods of time the effects can be dramatic.
• About 300 million years ago, the Earth consisted of a single continent, Pangaea. Since that time,
plate tectonic processes have moved the Earth’s plates to form the Earth we see today.
• There a a few dozen tectonic plate that make up the Earth’s surface. Some are continental and
some are oceanic. They can be very big (the Pacific Plate) or very small (the Juan de Fuca
plate). Their movement over time gives the Earth its current appearance.
• Oceanic plates have an important role in the history of the Earth because they are recycled over
time. New crust appears at oceanic ridges, which can be as much as 40,000 miles long. Old
crust “dives down” (is subducted) into the Earth’s mantle in other parts of the ocean.
• Rock in the mantle is very hot and is constantly moving because of a process called convection.
As the rock in the mantle moves, it moves the tectonic plates on the surface of the Earth.
• Earthquakes are one result of plate tectonic activity. Earthquakes occur at plate boundaries and
happen when two plates sliding side by side stick to one another, building up pressure that
eventually needs to be released.
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WHY WE’RE
ALL LAVA SURFERS
Article / Peter Stark
• The author, Peter Stark, is from Montana – right in the middle of the North American plate.
Continental plates, he explains, are always in motion, which makes us all lava surfers.
• Stark has visited places where it’s possible to experience the motion of continental plates, which
is also called plate tectonics.
• He describes his investigations of earthquake and volcanic activity in Indonesia, which got him
interested in plate tectonics and the nature of the Indonesian archipelago.
• He also describes a visit to Iceland, an island where two different plates move away from each
other. While there, he explored a spot where “volcanic fire mingled with glacial ice.”
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INTRODUCTION TO GEOLOGY
Video Talk / Walter Alvarez
• Geology is the study of the Earth. There are two major types of geologists: Those that study
Earth processes, like volcanic eruptions or the movement of glaciers, and those that study Earth
history.
• Because liquids and gases are always moving but solids stay the same for long periods of time,
rocks preserve a record of the Earth’s history. Using rocks, for example, we can see sediment
from the asteroid that caused the extinction of the dinosaurs and we can see evidence of plate
tectonics.
• Geologists rely on both simple tools, like the hammer and the compass, and more complex
ones, like electron microprobes (which allow chemical analysis of grains of minerals), electron
microscopes (for studying the parts of a sample that are invisible to the naked eye), and mass
spectrometers (for determining the age of a sample).
• Geologists study rocks to better understand plate tectonic processes, to answer questions about
life and why it was able to evolve on Earth, and to better understand climate, as rocks can
provide clues about temperature and moisture in the past.
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ALFRED WEGENER
& HARRY HESS
Article / Cynthia Stokes Brown
• Alfred Wegener was trained as a meteorologist, but he had many scientific interests and he was
intrigued by the jigsaw puzzle fit of the continents.
• Wegener believed that plant and animal evidence and the distribution of mountain chains
showed that the continents were once connected in one big land mass he called Pangaea. He
proposed the idea of continental drift to explain how the continents had moved into their current
configuration.
• Harry Hess was a geologist who used modern sonar equipment to study the ocean floor. He
discovered that the ocean floor was not flat, but rather, covered with mountain ranges and
trenches. He helped develop the idea of seafloor spreading, the idea that new crust is created at
ocean ridges. These discoveries helped turn Wegener’s ideas about continental drift into the
theory of plate tectonics.
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ERATOSTHENES
Article / Cynthia Stokes Brown
• Eratosthenes made some important contributions to our collective learning about the Earth,
combining naked-eye observations and mathematics.
• Eratosthenes was interested in a number of questions about Earth processes. He calculated the
tilt of the Earth, the distance from the Earth to the Moon and the Sun, and was also interested in
mapping points on the surface of the Earth.
• The idea that the Earth was round was not new to educated Greeks; they had proofs for this
belief. They noted that when a ship sailed over the horizon, it did not suddenly disappear from
sight. Rather the ship disappeared before the top of its masts. They also noted the curved
shadow of the Earth on the Moon during lunar eclipses.
• Eratosthenes great achievement was developing a mathematical proof that the Earth was round.
Eratosthenes measured the angle of the Sun’s shadow in two wells in two Egyptian cities on the
summer solstice. He knew the distance between the two cities, and he used math to calculate
the circumference of the Earth from the data he collected. His calculation was close to the actual
value we know today.
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INTRODUCTION TO THE
GEOLOGIC TIME CHART
Video Talk / Walter Alvarez
• Geologic processes unfold over millions or billions of years. The size and variety of timescales
that geologists have to deal with has led geologists to organize this information into a geologic
timescale.
• This timescale is based on the concept of periodization, the idea of breaking history into chunks.
• Periodization in geology is the result of a very formal process. Geologists make decisions about
periodization at the international level to ensure there is agreement about them. This process
can be very different from what happens with historians, who do not always agree on
periodization. Historians can disagree on when an important period like the Renaissance
started, or they can argue that it started at different times in different places.
• Geologists use very specific terminology to refer to different geological periods. In order from the
longest to the shortest, they are: Eons, eras, periods, epochs and ages.
• Eons are the longest periods of geological history. Each of the Earth’s eons was very different. In
the Hadean period, the Earth was hot and the rate of change was very fast. In the Archaean and
Proterozoic eons, the Earth had cooled and the rate of change slowed. The pace of change
increased again in the Phanerozoic because of the appearance of more complex life forms.
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PRINCIPLES OF GEOLOGY
Article / Charles Lyell
• Charles Lyell (1797 –1875) was a British lawyer and the foremost geologist of his day. He is best
known as the author of Principles of Geology, from which this article is excerpted.
• Principles of Geology popularized geologist James Hutton’s concept of “uniformitarianism” —
the idea that the Earth was shaped by slow-moving forces still in operation today.
• Uniformitarian ideas opposed the common belief among many geologists that unique
catastrophes or supernatural events, like the biblical flood in the story of Noah, shaped Earth’s
surface. The motto of uniformitarianism was “the present is the key to the past.”
• Lyell’s friend, Charles Darwin, took the idea of uniformitarianism and extended it to biology.
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LOOKING AHEAD
WHAT’S NEXT?
In Unit 5, we will focus on the origin and evolution of life on our planet, Earth. We will learn:
• About the conditions required for the emergence of life.
• What similarities exist across all living things.
• How life has changed over time, evolving from simple life forms to complex organisms.
• How life is affected by changes in astronomical, geological, and biological conditions.
• How DNA enables living things to pass adaptations to new generations.
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