objectives vocabulary
DESCRIPTION
The Early Earth Earth’s “Birth” For about the first 4 billion years of Earth’s 4.6-billion-year existence, most of the life-forms that inhabited Earth were unicellular organisms. In 1996, the announcement that a meteorite from Mars might contain microscopic fossils of bacteria rekindled scientific interest in the search for life elsewhere in the universe. It may be possible to identify clues to the possible existence of life on other planets through rocks from those planets.TRANSCRIPT
Objectives Vocabulary
The Early Earth Objectives Describe the evidence used to determine
the ageof Earth. Understand why scientists theorize that the early
Earth was hot. Vocabulary zircon asteroid meteorite The Early Earth
Earths Birth For about the first 4 billion years of
Earths4.6-billion-year existence, most of the life-forms that
inhabited Earth were unicellular organisms. In 1996, the
announcement that a meteorite from Mars might contain microscopic
fossils of bacteria rekindled scientific interest in the search for
life elsewhere in the universe. It may be possible to identify
clues to the possible existence of life on other planets through
rocks from those planets. The Early Earth Earths Birth There is
evidence of lifes beginnings on Earth in Precambrian rocks. Most of
Earths history is contained within the4 billion years that make up
the Precambrian. The Early Earth How old is Earth? We know that
Earth must be at least as old as the oldest rocks in the crust. The
age of the oldest rocks on Earth is between to 3.8 billion years.
Evidence of 4.1- to 4.2-billion-year-old crust exists in the
mineral zircon that is contained in metamorphosed sedimentary rocks
in Australia. Zircon is a very stable mineral that commonly occurs
in small amounts in granite. The Early Earth How old is Earth?
Meteorites have been radiometrically dated at between 4.5 and 4.7
billion years old. The oldest rock samples from the Moon are
approximately 4.6 billion years old. Scientists commonly agree that
the age of Earth is4.6 billion years. The Early Earth Earths Heat
Sources Earth was most likely extremely hot shortly afterit formed,
and there were three likely sources of this heat. The first source
was radioactivity. Radioactive isotopes were more abundant during
the past. One product of radioactive decay is energy, which
generates heat. The Early Earth Earths Heat Sources The second
source of Earths heat was the impact of asteroids and meteorites.
Asteroids are metallic or silica-rich objects that are 1 km to 950
km in diameter. Meteoroids are small asteroids or fragmentsof
asteroids. Meteorites are meteoroids that fall to Earth. Evidence
suggests that collisions, which generate a tremendous amount of
thermal energy, were much more common throughout the early solar
system than they are today. The Early Earth Earths Heat Sources The
third source of Earths heat was gravitational contraction. As a
result of meteor bombardment and subsequent accumulation of
meteorite material on Earth, the size of Earth increased. The
weight of the material caused gravitational contraction of the
underlying zones, the energy of which was converted to thermal
energy. The new material also caused a blanketing effect, which
prevented the newly generated heat from escaping. Section
Assessment 1. How are meteorites evidence of Earths age?
The Early Earth Section Assessment 1.How are meteorites evidence of
Earths age? Most astronomers agree that the solar system formed at
the same time as Earth, and therefore, Earth and meteorites should
be about the same age. The Early Earth Section Assessment 2.What
are were the three likely sources of heat on Earth shortly after it
formed? The three sources of heat were likely radioactive decay,
the impact of asteroids and meteorites, and gravitational
contraction. The Early Earth Section Assessment 3.Identify whether
the following statements are true or false. ______ The Precambrian
represents about half of Earths existence. ______ The oldest rocks
on Earth are between 3.96 and 3.8 billion years. ______Meteorites
are asteroids that fall to Earth. ______A meteorite could possibly
provide evidence of life on another planet. false true End of
Section 1 Objectives Vocabulary Explain the origin of Earths
crust.
Formation of the Crust and Continents Objectives Explain the origin
of Earths crust. Describe the formation of the Archean
andProterozoic continents. Vocabulary differentiation Precambrian
shield Canadian Shield microcontinent Laurentia Formation of the
Crust and Continents
Early in the formation of Earth, the planet was molten, and
numerous elements and minerals were mixed throughout the magma.
Over time, the minerals became concentrated in specific zones and
Earth became layered. As the magma reached the surface and cooled,
landmasses began to form. Formation of the Crust and
Continents
When Earth formed, iron and nickel, which are dense elements,
concentrated in its core. Lava flowing from the interior of Earth
concentrated the less-dense minerals near the surface of Earth over
time. The denser minerals, which crystallize at higher
temperatures, concentrated deeper within Earth and formed the rocks
that make up Earths mantle. Formation of the Crust and
Continents
Differentiation is the process by which a planet becomes internally
zoned when heavy materials sink toward its centerand lighter
materialsaccumulate near itssurface. Formation of the Crust and
Continents Formation of the Crust and Continents
Earths earliest crust most likely formed as a result of the cooling
of the uppermost mantle and was similar to basalt. As
sediment-covered slabs of the crust were recycled into the mantle
at subduction zones, the slabs partly melted and generated magmas
with different mineral compositions. These magmas crystallized to
form the first granitic continental crust, which was rich in
feldspar, quartz, and mica. Formation of the Crust and
Continents
The formation of the majority of crustal rocks was completed by
about 2.5 billion years ago. As less-dense material has a tendency
to float on more-dense material, continental crust floats on top of
the mantle below it. Basaltic crust is more dense than granitic
crust, and therefore, it does not float as high on the mantle.
Formation of the Crust and Continents The Cores of the
Continents
Formation of the Crust and Continents The Cores of the Continents A
Precambrian shield is a core of Archean and Proterozoic rock that
forms the core of each continent. Buried and exposed parts of a
shield together compose the craton, which is the stable part of a
continent. The Canadian Shield is the name for the Precambrian
shield in North America because much of it is exposed in Canada.
The Cores of the Continents
Formation of the Crust and Continents The Cores of the Continents
Formation of the Crust and Continents
Growth of Continents Microcontinents, which were small pieces of
continental crust that formed during the Archean, began to collide
as a result of plate tectonics early during the Proterozoic. At
each of these collision sites, the Archean microcontinents were
sutured or fused togetherat orogens. These orogens are belts of
rocks that were deformed by the immense energy of the colliding
continents. Formation of the Crust and Continents
Growth of Continents Laurentia, the ancient continent which was
assembled1.8 billion years ago, would become the core of modern-day
North America. Formation of the Crust and Continents
Growth of Continents Near the end of the Early Proterozoic, between
1.8 and 1.6 billion years ago, volcanic island arcs collided with
the southern margin of Laurentia. The final phase of Proterozoic
growth of Laurentia, the Grenville Orogeny, occurred between 1.2
billion and 900 million years ago. By the end of the Proterozoic,
nearly 75 percent of present-day North America had formed.
Formation of the Crust and Continents
Growth of Continents By the end of the Proterozoic, all of the
major masses of continental lithosphere had formed. As the
lithospheric plates moved around, they periodically collided and
sutured together to form Rodinia, the first supercontinent. Rodinia
began to break apart at the end of the Proterozoic and continued to
do so during the Early Phanerozoic. Formation of the Crust and
Continents
Growth of Continents Formation of the Crust and Continents
Section Assessment 1.Match the following terms with their
definitions. ___ differentiation ___Precambrian shield ___
microcontinent ___ Laurentia A B D C A.the process by which a
planet becomes internally zoned B.a core of Archean and Proterozoic
rock that forms the core of continents. C.the ancient continent
that formed the core of modern-day North America D.small pieces of
continental crust that formed during the Archean Section Assessment
2. What is the Canadian Shield?
Formation of the Crust and Continents Section Assessment 2.What is
the Canadian Shield? The Canadian Shield is the Precambrian shield
in North America. It is called the Canadian Shield because much of
it is exposed in Canada. Formation of the Crust and
Continents
Section Assessment 3.Why do the rocks of the earliest crust
nolonger exist? The rocks of the earliest crust no longer exist
because they were recycled in subduction zones long ago. End of
Section 2 Objectives Vocabulary
Formation of the Atmosphere and Oceans Objectives Describe the
formation of Earths atmosphere and oceans. Identify the origin of
oxygen in the atmosphere. Explain the evidence that oxygen existed
in the atmosphere during the Proterozoic. Vocabulary cyanobacteria
stromatolite banded iron formation red bed Formation of the
Atmosphere and Oceans
Earths early atmosphere was nothing like what it is today. The
oxygen that early forms of algae produced through the process of
photosynthesis affected the development of life on Earth in two
very important ways. It changed the composition of the atmosphere
and thus made life possible for oxygen-breathing animals. It
produced the ozone layer that filters ultraviolet (UV) radiation.
The Precambrian Atmosphere
Formation of the Atmosphere and Oceans The Precambrian Atmosphere
Hydrogen and helium probably dominated Earths earliest atmosphere
but probably escaped into space due to their small masses. Gases
that have greater masses, such ascarbon dioxide and nitrogen,
cannot escape Earths gravity. Considerable volcanic activity during
the Early Precambrian released tremendous amounts of gases into the
atmosphere through the process of outgassing. The Precambrian
Atmosphere
Formation of the Atmosphere and Oceans The Precambrian Atmosphere
The most abundant gases vented from volcanoes are water vapor
(H2O), carbon dioxide (CO2), nitrogen (N2), and carbon monoxide
(CO). Many geologists hypothesize that outgassing formed Earths
early atmosphere. In addition, the early atmosphere most likely
contained methane (CH4) and ammonia (NH3). Argon (Ar) also began to
accumulate during the Early Precambrian. Oxygen in the
Atmosphere
Formation of the Atmosphere and Oceans Oxygen in the Atmosphere
There was no oxygen in the atmosphere during the Precambrian. The
oldest known fossils, which are about 3.5 billion years old, are
the remains of tiny, threadlike chlorophyll-bearing filaments of
cyanobacteria. Ancient cyanobacteria used photosynthesis to produce
the nutrients they needed to survive, giving off oxygen as a waste
product. Oxygen in the Atmosphere
Formation of the Atmosphere and Oceans Oxygen in the Atmosphere
Oxygen Producers The abundance of cyanobacteria increased
throughout the Archean until they became truly abundant during the
Proterozoic. Stromatolites, which are large mats and mounds of
billions of cyanobacteria, dominated the shallow oceans of the
Proterozoic. Oxygen in the Atmosphere
Formation of the Atmosphere and Oceans Oxygen in the Atmosphere
Evidence in the Rocks Iron oxides are identified by their red color
and provide undeniable evidence of free oxygen in the atmosphere.
Evidence indicates that there was little or no free oxygen in the
atmosphere throughout most of the Archean. Near the end of the
Archean and by the beginning of the Proterozoic, photosynthesizing
stromatolites in shallow marine water increased oxygen levels in
localized areas, which caused banded iron formations to form.
Oxygen in the Atmosphere
Formation of the Atmosphere and Oceans Oxygen in the Atmosphere
Evidence in the Rocks Banded iron formations are deposits which
consist of alternating bands of chert and iron oxides. Red beds are
sedimentary rocks that are younger than 1.8 billion years and rusty
red in color. The presence of red beds in rocks that are
Proterozoic and younger is strong evidence that the atmosphere by
this time contained free oxygen. Formation of the Atmosphere and
Oceans
Importance of Oxygen Oxygen is important because most animals
require it for respiration and it provides protection against UV
radiation from the Sun. Earth is naturally protected from this
radiation by ozone (O3) molecules that are present in the lower
part of Earths upper atmosphere. Oxygen in Earths atmosphere that
was produced mainly through photosynthesis also contributes to the
ozone layer. Nearly all the oxygen that is present was released
into the atmosphere by photosynthesis. Formation of the
Oceans
Formation of the Atmosphere and Oceans Formation of the Oceans
Oceans are thought to have originated largely from the same process
of outgassing that formed the atmosphere. As the early atmosphere
and the surface ofEarth cooled, the water vapor condensed toform
liquid water. During the Archean, tremendous amounts of rain slowly
filled the low-lying, basalt-floored basins, thus forming the
oceans. Formation of the Oceans
Formation of the Atmosphere and Oceans Formation of the Oceans
Dissolved minerals made the oceans of the Precambrian salty just as
they make the oceans salty today. A recent hypothesis suggests that
some of Earths water may have come from the bombardment of
microcomets, or small comets made of frozen gas and water. Oxygen
in the Atmosphere
Formation of the Atmosphere and Oceans Oxygen in the Atmosphere
Oxygen Causes Change The Precambrian began with an oxygen-free
atmosphere and simple life-forms. This oxygen added by
cyanobacteria not only enabled new life-forms to evolve, but it
also protected Earths surface from the Suns UV rays. Oceans formed
from abundant water vapor in the atmosphere and possibly from outer
space. Earth was then a hospitable place for new life-formsto
inhabit. Formation of the Atmosphere and Oceans
Section Assessment 1.Match the following terms with their
definitions. ___ cyanobacteria ___ stromatolite ___ banded
ironformation ___ red bed D B C A A.sedimentary rocks that are
younger than 1.8 billion years and are rusty red in color B.large
mats and mounds of cynobacteria C.deposits that consist of
alternating bands of chert and iron oxides D.chlorophyll containing
bacteria that may be responsible for the addition of oxygen to
Earths early atmosphere Formation of the Atmosphere and
Oceans
Section Assessment 2.Why is Earths current atmosphere rich in
carbon dioxide and nitrogen? Gases that have greater masses, such
as carbon dioxide and nitrogen, cannot escape Earths gravity like
lighter gases such as hydrogen and helium. Formation of the
Atmosphere and Oceans
Section Assessment 3.Identify whether the following statements are
true or false. ______ Stromatolites currently exist on Earth.
______ Free oxygen is released during outgassing. ______Around half
of the oxygen that we breathe today was released into the
atmosphere through photosynthesis. ______There was little free
oxygen in the atmosphere during the Archean. true false End of
Section 3 Objectives Vocabulary
Early Life on Earth Objectives Describe the experimental evidence
of how life developed on Earth. Distinguish between prokaryotes and
eukaryotes. Identify when the first multicellular animals appeared
in geologic time. Vocabulary amino acids hydrothermal vent
prokaryote eukaryote Varangian Glaciation Ediacara fauna Early Life
on Earth Origin of Life on Earth Fossil evidence indicates that
life existed on Earth about 3.5 billion years ago. Earth probably
could not have supported life until about 3.9 billion years ago
because meteorites were constantly striking its surface. This
places the origin of life somewhere between 3.9 and 3.5 billion
years ago. Origin of Life on Earth Experimental Evidence
Early Life on Earth Origin of Life on Earth Experimental Evidence
Molecular biologists in the 1920s also suggested that an atmosphere
containing abundant ammonia and methane but lacking free oxygen
would be an ideal setting for the primordial soup in which life may
have begun. Stanley Miller and Harold Urey set up an apparatus that
contained a chamber filled with hydrogen, methane, and ammonia to
simulate the early atmosphere. Sparks from tungsten electrodes
simulated lightning in the atmosphere. Origin of Life on Earth
Experimental Evidence
Early Life on Earth Origin of Life on Earth Experimental Evidence
Their atmospheric chamber was connected to a lower chamber that was
designed to catch any particles that condensed in the atmospheric
chamber. Only one week after the start of the experiment, the lower
chamber contained organic molecules such as cyanide (CN),
formaldehyde (H2CO), and four different amino acids. Amino acids
are the building blocks of proteins,the basic substances from which
life is built. Origin of Life on Earth Experimental Evidence
Early Life on Earth Origin of Life on Earth Experimental Evidence
Continued experiments showed that 13 of the 20 amino acids known to
occur in living things could be formed using the Miller-Urey
method. Further experiments demonstrated that heat, cyanide, and
certain clay minerals could cause amino acids to join together in
chains like proteins. Miller and Urey demonstrated that however
life first formed, the basic building blocks of life were most
likely present on Earth during the Archean. Origin of Life on Earth
The Role of RNA
Early Life on Earth Origin of Life on Earth The Role of RNA The
nucleic acids RNA and DNA are the basic requirements for
reproduction, an essentialcharacteristic of life. In modern
organisms, DNA carries the instructions necessary for cells in all
living things to function. RNA ribozymes, unlike DNA, can replicate
without the aid of enzymes, and may have been the first replicating
molecules on Earth. An RNA-based world may have been intermediate
between an inorganic world and the DNA-based organic world that
followed. Origin of Life on Earth Hydrothermal Vents and the
Beginnings of Life
Early Life on Earth Origin of Life on Earth Hydrothermal Vents and
the Beginnings of Life Life on Earth may have originated deep in
the ocean, near active volcanic seafloor rifts. Hydrothermal vents
are the openings where hot water rises and is expelled from the
ocean floor. All of the energy and nutrients necessary for
theorigin of life are present at these deep-sea hydrothermal vents.
Some scientists hypothesize that during the Archean, near
hydrothermal vents, amino acids joined together on the surfaces of
clay minerals to form proteins. Early Life on Earth Proterozoic
Life The only evidence of life-forms that existed before the
Proterozoic is the fossilized remains of unicellular organisms
called prokaryotes. A prokaryote is an organism that is composed of
a single cell, which does not contain a nucleus and is the simplest
kind of cell. A eukaryote is an organism that is composed of a cell
or cells that contain a nucleus. Early Life on Earth Proterozoic
Life The Varangian Glaciation was a widespread glaciation event
that occurred between 800 and 700 million years ago that played a
critical role in the extinction of many members of a group of
possible eukaryotes, the acritarchs. Shortly after the ice
retreated toward the poles, 700 million years ago, multicellular
organisms first appeared in the fossil record. Early Life on Earth
Ediacara Fossils Fossils collectively referred to as the Ediacara
fauna are the impressions of soft-bodied organisms that were
discovered in Late Proterozoic rocks in the Ediacara Hills of
southern Australia. Early Life on Earth Ediacara Fossils It is
generally agreed that these fossils represent animals that were
composed of different types of eukaryotic cells. Scientists are
unsure, however, whether the Ediacara fauna are relatives of modern
animal groups or whether they were completely different types of
organisms. The Ediacara fauna seem to provide fossil evidence of an
ancestral stock of complex Proterozoic animals. Early Life on Earth
Ediacara Fossils Some scientists consider the similarity in shape
to animals in other phyla coincidental and that the Ediacara fauna
represents a virtual dead end. Ediacara fossils have been found in
all parts of the world. These organisms seem to have flourished
between 670 and 570 million years ago until an apparent mass
extinction. Early Life on Earth Section Assessment 1.Match the
following terms with their definitions. ___ prokaryotes ___
eukaryotes ___ amino acids ___ Ediacara fauna B A D C A.organisms
that are composed of cells that contain a nucleus B.an organism
that is composed of a single cell, which does not contain a nucleus
C.fossils of soft-bodied organisms that were discovered in Late
Proterozoic rocks D.the building blocks of proteins Section
Assessment 2. When did life most likely develop on Earth?
Early Life on Earth Section Assessment 2.When did life most likely
develop on Earth? The origin of life is somewhere between3.9 and
3.5 billion years ago. Early Life on Earth Section Assessment
3.Identify whether the following statements are true or false.
______ RNA can be easily synthesized underconditions that likely
existed at the surface ofthe Archean Earth. ______ Ediacara fauna
may not represent an ancestral stock of any modern group.
______Life is currently being synthesized athydrothermal vents.
______Cyanobacteria are examples of prokaryotes. false true End of
Section 4 Chapter Resources Menu
Study Guide Section 22.1 Section 22.2 Section 22.3 Section 22.4
Chapter Assessment Image Bank Chapter Resources Menu Section 22.1
Study Guide Section 22.1 Main Ideas Geologists have used
radiometric dating to show that Earth must be at least 4.2 billion
years old. Because the solar system formed all at the same time,
Moon rocks and meteorites that are approximately 4.6 billion years
old suggest that Earth is also 4.6 billion years old. The early
Earth was a very hot place because of abundant radioactive
isotopes, bombardment by meteorites, and gravitational contraction.
Section 22.2 Study Guide Section 22.2 Main Ideas Earths early crust
formed by the cooling of the uppermost mantle. This early crust
weathered and formed sediments. Sediment-covered slabs of this
early crust were subducted and generated magmas that contained
granitic minerals. During the Archean, microcontinents collided
with one another throughout the Proterozoic and formed the cores of
the continents. By the end of the Proterozoic, the first
supercontinent, Rodinia, had formed. Section 22.3 Study Guide
Section 22.3 Main Ideas Earths early atmosphere and the oceans
formed mainly by the process of outgassing. Nearly all of the
oxygen in the atmosphere is a result of photosynthesis. Certain
minerals oxidize, or rust, in the presence of free oxygen.
Proterozoic red beds are sedimentary rock deposits that contain
oxidized iron. They are the evidence that there was free oxygen in
the atmosphere during the Proterozoic. Section 22.4 Study Guide
Section 22.4 Main Ideas All the ingredients were present on the
early Earth to form proteins, the building blocks of life. Amino
acids, the molecules that make up proteins, were likely abundant on
the surface of the early Earth. Prokaryotic cells are generallly
small and contain no nuclei. Eukaryotic cells contain nuclei and
are generally larger and more complex than prokaryotic cells. The
first evidence of multicellular animals is fossils of 2.1 billion
year old eukaryotic algae. Multiple Choice 1. Approximately how old
are Earths oldest rocks?
Chapter Assessment Multiple Choice 1.Approximately how old are
Earths oldest rocks? a.2.4 billion yearsc.3.9 billion years b.3.2
billion yearsd.4.6 billion years Radiometric dating has determined
that the age of the oldest rocks on Earth is between 3.96 and 3.8
billion years. Multiple Choice 2. What was the first supercontinent
called?
Chapter Assessment Multiple Choice 2.What was the first
supercontinent called? a.Rodiniac.Pangaea b.Laurentiad.Gondwanaland
Rodinia formed approximately 750 million years ago. Laurentia was
the ancient continent that today forms the core of North America.
Pangaea was the most recent supercontinent that began to break
apart 200 million years ago. Gondwanaland was a supercontinent that
formed near the south pole during the Late Paleozoic. Chapter
Assessment Multiple Choice 3.Which organism may have been
responsible for introducing mass quantities of oxygen into Earths
atmosphere? a.stromatolitesc.Ediacara fauna
b.cyanobacteriad.eukaryotes Cyanobacteria were
chlorophyll-containing prokaryotes that relied on photosynthesis
and gave off oxygen as a by-product. Large mats and mounds of
billions of cyanobacteria called stromatolites dominated the
shallow waters of the Proterozoic. Chapter Assessment Multiple
Choice 4.Which of the following is likely the same ageas Earth?
a.zirconc.meteors b.red bedsd.banded iron formations Astronomers
generally agree that the bodies in the solar system, including
Earth, formed at about the same time. Meteorites have been
radiometrically dated at between 4.5 and 4.7 billion years old.
Chapter Assessment Multiple Choice 5.Which of the following offers
the strongest evidence of abundant free oxygen in the atmosphere?
a.red bedsc.oceans b.active volcanoesd.none of the above Red beds
would offer the strongest evidence of atmospheric free oxygen
because free oxygen is needed to react with the iron causing the
reddish color in the rock. Volcanoes and oceans do not add free
oxygen to the atmosphere by themselves. Short Answer 6. What is the
process of differentiation?
Chapter Assessment Short Answer 6.What is the process of
differentiation? Differentiation is the process by which a planet
becomes internally zoned when heavy materials sink toward its
center and lighter materials accumulate near its surface. Short
Answer 7. When and where did the Ediacara organisms flourish?
Chapter Assessment Short Answer 7.When and where did the Ediacara
organisms flourish? The Ediacara organisms were widely distributed
throughout the shallow oceans of the Late Proterozoic. They seemed
to have flourished between 670 and 570 million years ago. Chapter
Assessment True or False 8.Identify whether the following
statements are true or false. ______ During the Varangian
Glaciation, the glacial iceadvanced almost to the equator. ______
Asteroids are usually smaller than 1 km across. ______Processes
which modify a system are knownas feedback. ______ DNA can
replicate without the help of enzymes. ______ By the end of the
Proterozoic, all of the majormasses of continental lithosphere had
formed. true false Image Bank Chapter 22 Images Image Bank Chapter
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