CHAPTER 8—EARLIEST EARTH: 2,100,000,000 YEARS
OF THE ARCHEAN EON
CHAPTER OVERVIEW
This chapter opens with a short presentation of basic astronomy to place Earth in context with the rest of
the Universe. Our solar system is a small part of a much larger aggregate of stars, planets, dust, and
gases called a galaxy. Our galaxy, the Milky Way, contains the sun and the nine planets that orbit around
it.
The most widely proposed theories of the origin of the universe must conform to an important
astronomical observation called the “red shift.” The red shift theory is examined along with the big bang,
steady-state cosmology, and oscillating universe cosmology theories. The development of the solar
system is attributed to the nebular hypothesis, which is explained in detail and verified by meteorites
found on Earth. This is followed by a solar system tour from center to fringe explaining the composition
and atmosphere of the nine planets. After the comprehensive detailed review of the solar system, the
differentiation of Earth is discussed followed by an explanation of the development of the atmosphere and
the “hydrologic” cycle.
The structural features of the Archean, shields, platforms, and cratons, along with the two major rock
associations, granulites and greenstones, are discussed in terms of their relationship to plate tectonics.
The chapter concludes with a detailed discussion of the origin of life on Earth. This includes the role of the
Earth’s mid-oceanic ridges and the ocean itself in this process. The earliest life forms of “The First Two
Billion Years” are described, noting the associations of the anaerobic, aerobic, prokaryotes, eukaryotes,
heterotrophs, autotrophs, and the fossil record left by these earliest forms. The Archean was the eon
when basic mechanisms governing geologic change were established and it was the time when life
appeared.
LEARNING OBJECTIVES
By reading and completing information within this chapter, you should gain an understanding of the
following concepts:
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Discuss the theories of the origin of the universe, solar system, and planet Earth.
Explain the astronomical observation of the red shift in explaining the origin of the universe.
Describe the role of meteorites in the formation of the Earth and the other planets.
Briefly compare the composition of the nine planets and their atmospheres.
Discuss how the Earth became differentiated into three distinct layers: the core, the mantle,
and the crust.
Discuss the evolution of the Earth’s atmosphere and the development of the “hydrologic”
cycle.
Define the dominant structural features of the Archean Eon: shields, cratons, and platforms
and how they relate to plate tectonics.
Locate the major Pre-Cambrian shield areas on a map: Canadian shield, Baltic shield,
Patagonian shield, etc.
Discuss the formation of the two major rock associations known as granulites and
greenstones.
Describe characteristics that separate life forms of the Archean: anaerobic, aerobic,
prokaryotes, eukaryotes, heterotrophs and autotrophs.
Describe the fossil record of the Archean and the importance of stromatolites.
Explain what molecular fossils are and describe where they have been found.
CHAPTER OUTLINE
I.
Earth in Context: a Little Astronomy
A. The Solar Nebula Hypothesis
B. Meteorites: Samples of the Early Solar System
Chapter 8—Earliest Earth: 2,100,000,000 Years of the Archean Eon
II.
A Solar System Tour
A. The Sun
1. Distance from the Sun
2. Earth’s Rotation
3. Earth’s Atmosphere
B. The Four Inner Planets
1. Mercury: Hot, Pockmarked and Swift
2. Venus: Nothing We Know Could Survive Here
3. Earth: The Best of All Possible Worlds
4. Earth’s Moon
5. Mars: Once Wetter, Warmer and Host to Life
6. The Asteroid Belt
C. The Five Outer Planets
1. Jupiter and Saturn: Giant Gas Balls
2. Uranus and Neptune: The Twin Planets
3. Pluto: An Outlier
III.
Following Accretion, Earth Differentiates
A. The Archean Crust
IV.
The Primitive Atmosphere
A. Growing an Oxygen-Rich Atmosphere
B. Geologic Clues to Early Atmosphere
V.
The Primitive Ocean and the Hydrologic Cycle
VI.
Origin of Precambrian “Basement” Rocks
A. Where Can We See Precambrian Rocks
B. Continental Crust Appears Worldwide
C. The Earliest Plate Tectonics
1. Granulites and Greenstones
2. Archean Sedimentation
VII.
The Origin of Life
A. How Molecules Might Combine to Start Life
B. Pulling Together the Pieces of Life
C. Simulating the Origin of Life
D. Where Did Life Begin
E. Hyperthermophiles and Chemosynthesis
F. Life in Extremely Hostile Environments
G. Feeding Life on Earth
H. Prokaryotes and Eukaryotes
I. Archean Fossils
J. Molecular Fossils
VIII.
In Retrospect
Chapter 8—Earliest Earth: 2,100,000,000 Years of the Archean Eon
KEY TERMS
(Pages 207–241)
accretion (210): In the development of protoplanets, the process of accumulation of bits of matter around
an initial mass.
aerobic organism (235): An organism that uses oxygen in carrying out respiratory processes.
anaerobic organism (235): An organism that does not require oxygen for respiration, but rather makes
use of processes such as fermentation to obtain its energy.
anorthosite (226): These intrusive gabbroic rocks are associated with tonalities, granodiorites, and
granites that form the granulite association.
Archean Eon (224): Division of the Precambrian time from 3800 million years to 2500 million years ago.
Origin of life began in the eon.
autotroph (234): An organism that uses an external source of energy to produce organic nutrients from
simple inorganic chemicals.
banded iron formation (BIF) (223): A rock that consists of alternating bands of iron-rich minerals,
generally hematite, and chert or fine-grained quartz.
Canadian shield (225): The most extensive exposure of Precambrian rocks in North America. This
geologically stable region extends across 3 million square miles.
carbonaceous chondrite (211): Meteorites that take their name from spherical bodies called chondrites
which contain nitrogen, hydrogen, carbon, dark iron, and magnesium silicates and water.
chemosynthesis (232): A means by which organisms derive their energy by oxidizing such inorganic
substances as hydrogen sulfide or ammonia.
chondrules (211): Spherical bodies that are solidified molten droplets splashed into space during an
impact that are found in chondrites.
craton (225): The long-stable region of a continent, commonly with Precambrian rocks either at the
surface or only thinly covered with younger sedimentary rocks.
differentiation (planetary) (219): The process by which a planet becomes internally zoned, as when
heavy materials sink toward its center and light materials accumulate near the surface.
eukaryote (235): A type of living cell containing a true nucleus, enclosed within a nuclear membrane, and
having well-defined chromosomes and cell organelles.
felsic (225): Meaning rich in feldspars, quartz, and muscovite, as the continental crust.
fermenter (234): The partial breakdown of organic compounds by an organism in the absence of oxygen.
The final product of fermentation is alcohol or lactic acid.
fusion (210): The molten state of a substance, or the change it undergoes to become molten.
granulite (226): A major rock association of the Archean cratons. Composed largely of gneisses derived
from strongly heated and deformed tonalities, granodiorites, and granites, as well as layered intrusive
gabbroic rocks called anorthosites.
greenstone (228): A major rock association of the Archean cratons. Usually occur in roughly trough-like
or synclinal belts. Prominent features of Archean terrains of all continents. Composed of basaltic,
andesitic, and rhyolitic volcanic rocks along with metamorphosed sediments derived by weathering and
derosion of the volcanics. Lavas of greenstone belts exhibit pillow structures that indicate that they were
extruded under water.
Chapter 8—Earliest Earth: 2,100,000,000 Years of the Archean Eon
heterotroph (235): An organism that depends on an external source of organic substances for its
nutrition and energy.
hydrologic cycle (224): The continuous recirculation of water by evaporation and precipitation—
processes powered by the sun and gravity.
hyperthermophile (232): Literally, high-heat lovers.
iron meteorite (212): Iron nickel. Asteroids are the probable source for iron meteorites.
komatiite (221): Ultramafic rocks that solidified from surface patches when the magma ocean cooled.
Formed at temperatures greater than 1100 degrees Centigrade, required to produce basalt. They reflect
the higher temperature gradients that prevailed during the late Hadean.
lithotroph (234): Subterranean microbes that have been dubbed “rock nourishment.” Most lithotrophs live
off energy derived from hydrogen, iron, magnesium, and sulfur.
lunar highlands (215): The lighter-hued craggy and heavily cratered regions of the moon.
mafic (225): Rocks (or lava) dominated by dark iron and magnesium silicates as is the oceanic crust.
magma ocean (220): The melting of the upper mantle during the early Archean infancy that may have
covered Earth’s surface.
maria (215): The darker areas of the moon. These darker areas form the floors of immense basins that
have been flooded with dark basaltic lava. (singular = mare)
meterorite (210): Meteors that survive the heat and reach the Earth’s surface.
molecular fossils (239): Preserved organic molecules that only eukaryotes can synthesize.
nebular hypothesis (209): The idea first suggested by German philosopher Immanuel Kant in 1755,
proposes that the solar system distilled from a rotating cloud of dust particles and gases called the solar
nebula.
ordinary chondrites (211): One of four meteorite compositions and are most abundant and at 4.6 billion
years old, are clearly Archean in age. Chondrites contain spherical bodies called chondrules that are
solidified molten droplets splashed into space during an impact.
organelles (230): Bodies capable of performing specific function.
outgassing (222): The process by which water vapor and other gases are released from the rocks that
held them and then vented to the surface.
partial melting (220): The variation in melting that occurs in different minerals in an original rock mass.
photoautotroph (235): Organisms that were capable of carrying on photosynthesis, the unique capability
of dissociating carbon dioxide into carbon and free oxygen.
photochemical dissociation (222): The process of water molecules into hydrogen and oxygen. The
process occurs in the upper atmosphere when water molecules are split by high-energy beams of
ultraviolet light from the sun.
photosynthesis (223): The process of synthesizing carbohydrates from carbon dioxide and water,
utilizing the radiant energy of light captured by the chlorophyll in plant cells.
platform (225): That part of a craton covered thinly by layered sedimentary rocks and characterized by
relatively stable tectonic conditions.
Precambrian (224): Term used to describe rocks that were older than the Cambrian Period
Chapter 8—Earliest Earth: 2,100,000,000 Years of the Archean Eon
Precambrian provinces (225): Divisions of the Canadian shield based on differences in the trends of
faults and folds, the style of folding, and the ages of component rocks.
prokaryote (235): Organisms that lack membrane-bounded nuclei and other membrane-bounded
organelles.
Proterozoic Eon (224): A younger divide of Precambrian time used to describe rocks.
protoplanet (210): Large globules formed from swarms of accreting bodies, dust, and gases. Enormously
larger than present-day planets. Each rotated somewhat like a miniature dust cloud, and each eventually
swept away most of the debris in its orbital path and was able to revolve around the central mass without
collision with other protoplanets. Formation required an estimated 10 million years.
shield (Precambrian) (225): Broadly upwarped, geologically stable regions of continents. Every
continent has one or more shields. The Canadian shield extends across 3 million square miles of northern
North America.
solar nebula (209): The rotating cloud of dust particles and gases from which the solar system was
derived.
solar system (208): In one galaxy of many located in the universe contains the Milky Way. Among the
Milky Way’s billions of stars is a small one, our sun. Around the sun swirl nine planets, thousands of
asteroids and comets, and countless bits of space debris that comprise the solar system.
solar wind (210): The stream of radiation from the sun, which drove enormous quantities of lighter
elements and frozen gases outward into space. This solar force is what causes a comet’s tail to show
wavy streaming or to be bent away from the sun. Also, this is the reason the planets closest to the sun
have smaller masses, but greater densities than the outer planets.
stony-iron meteorite (212): The least abundant of the meteorites. Derived from a shattered asteroid,
originating from the area in the asteroid that lies between the iron core and the surrounding rocky shell.
They are composed of silicate minerals and iron nickel.
stromatolite (236): Distinctly laminated accumulations of calcium carbonate having rounded, branching,
or frondose shape and believed to form as a result of the metabolic activity of marine algae. They are
usually found in the high intertidal to low supratidal zones. Associated with Cyanobacteria.
ultramafic (228): Rock or lava with extremely high concentrations of iron and magnesium.
Chapter 8—Earliest Earth: 2,100,000,000 Years of the Archean Eon
MULTIPLE-CHOICE QUESTIONS
1.
Theories for the origin of the universe must conform to an important astronomical observation
called
a. oscillating universe cosmology.
c. solar nebula.
b. big bang.
d. red shift.
2.
The process occurring in the upper atmosphere by which water molecules are split by high-energy
beams of ultraviolet light from the sun is termed
a. photochemical dissociation.
c. photoautotrophy.
b. photosynthesis.
d. outgassing.
3.
The process by which water vapor and other gases were released from rocks within the first billion
years of Earth’s history.
a. sublimation
c. outgassing
b. photosynthesis
d. photochemical dissociation
4.
When early geologists first began to describe local sequences of strata, they sometimes
encountered a primary or basement complex of metamorphic and igneous rocks that lay beneath
fossil-bearing sedimentary strata. The older more crystalline rocks came to be known as
a. Hadean.
c. Early Archean.
b. Proterozoic.
d. Precambrian.
5.
The most extensive exposures of Precambrian rocks are in geologically stable regions of continents
called
a. cratons.
c. Precambrian provinces.
b. platforms.
d. shields.
6.
Relatively thin blankets of sedimentary strata that cover regions of stable, basement rocks is
called a
a. craton.
c. Precambrian province.
b. platform.
d. shield.
7.
The Canadian shield is divided into several provinces on the basis of
a. fossil content.
b. structural trends and age dates.
c. the composition of the basement rocks.
d. sedimentary structures such as cross-bedding and paleocurrent directions.
8.
The Precambrian is ordered, from oldest to youngest, into the
a. Archean, Hadean, and Proterozoic Eons. c. Hadean, Archean, and Proterozoic Eons.
b. Proterozoic, Hadean, and Archean Eons. d. Proterozoic, Archean, and Hadean Eons.
9.
The upper most units of a greenstone sequence consist mostly of
a. mafic volcanic rocks.
c. marine sedimentary rocks.
b. felsic volcanic rocks.
d. terrestrial sedimentary rocks.
10.
Pillow lavas found in greenstone belts suggest
a. subaqueous eruptions.
c. intrusive feeder dikes from a nearby volcano.
b. ash flow deposits.
d. higher temperatures for the basalt being
extruded.
11.
Granulites are
a. sedimentary rocks composed of poorly sorted and angular igneous rock fragments.
b. metamorphic rocks formed from felsic igneous rocks by structural deformation and high
temperatures.
c. igneous rocks formed entirely of plagioclase feldspar.
d. metamorphic rocks formed from obducted oceanic crust.
Chapter 8—Earliest Earth: 2,100,000,000 Years of the Archean Eon
12.
The uppermost units of greenstone belts consist mainly of
a. ultramafic rocks.
c. sedimentary rocks.
b. basaltic rocks.
d. metamorphic rocks.
13.
Stanley Miller and Harold Urey, in 1953, circulated methane, ammonia, and hydrogen in an
apparatus recreating the Archean atmosphere. By supplying an electrical current they produced
a. amino acids.
c. ribonucleic acids.
b. nucleic acids.
d. hydrocarbons.
14.
Organisms that manufacture their own food from simple inorganic substances are called
a. fermenters.
c. heterotrophs.
b. bacteria.
d. autotrophs.
15.
The process whereby organisms release free oxygen (as a waste product) into the atmosphere is
called
a. respiration.
c. photosynthesis.
b. photochemical dissociation.
d. fermentation.
16.
An organism that can live in an oxygen-rich environment is called
a. aerobic.
c. planktonic.
b. anaerobic.
d. photosynthetic.
17.
An organism that uses an external source of energy to produce organic nutrients from simple
inorganic chemicals is a/an
a. aerobic.
c. autotroph.
b. mitochondria.
d. prokaryote.
18.
The province of eastern Canada that is the youngest, middle proterozoic region of the Canadian
shield and the last to experience a major orogeny is
a. Ontario.
c. Superior.
b. Grenville.
d. Labrador.
19.
These organisms reproduce sexually, with a union of egg and sperm to form the nucleus of a single
cell.
a. lithotrophs
c. autotrophs
b. eukaryotes
d. heterotrophs
20.
The granulite association which is composed largely of gneisses derived from deformed granitic
rocks, as well as more gabbroic rocks is called
a. komatiites.
d. rhyolites.
b. anorthosites.
e. graywackes.
c. andesites.
Chapter 8—Earliest Earth: 2,100,000,000 Years of the Archean Eon
FILL IN THE BLANK
1.
These stable regions where basement rocks are covered by relatively thin blankets of sedimentary
strata are called
.
2.
The term used for the continental crust that is rich in feldspar, quartz, and muscovite is called crust.
3.
The ultramafic rocks that reflect the higher temperature gradients that prevailed during the Hadean
are called
.
4. A mountain-building event that occurred in the late-Archeon Eon in Canada that created high
temperatures that melted rocks at depth and emplaced a gigantic batholite is called
.
5.
The theory concerning the origin of the universe that indicates that the universe is
expanding is
.
6.
The Archean rock association that is composed largely of gneisses derived from strongly-heated
and deformed tonalites, granodiorites and granites is
7. The Archean rock association in which felsic volcanics occur above mafic rocks which are overlain
by shales, graywackes, conglomerates and banded iron formations, is called
.
8.
Gneisses and layered intrusive gabbroic rocks form the Archean rock association are called:
.
9. The belt structures believed to be the remnants of a once highly-active volcanic trough or synclinal
belt are called
.
10.
An organism that uses an external source of energy to produce organic nutrients from simple
inorganic compounds is called a/an
.
11.
The type of prokaryote that produces its own food by the processes of photosynthesis and asexual
reproduction is called
.
12.
The early organisms that had a definite nuclear wall, well-defined chromosomes, and the capacity
for sexual reproduction are called
.
13.
The laminar, organic sedimentary structures formed by the trapping of sedimentary particles and
precipitation of calcium carbonate in response to the metabolic activities and growth of mat-like
colonies are called
.
14.
The idea that the solar system originated as a result of distilling from a rotating cloud of dust
particles is called the _____________ ______________.
15.
Modern Earth is a differentiated planet that has three very distinct layers: _____________,
____________, and _______________.
.
Chapter 8—Earliest Earth: 2,100,000,000 Years of the Archean Eon
TRUE/FALSE
1.
The “Big Bang” occurred between 3-5 billion years ago and marked the creation of the
solar system.
2.
The oscillating universe cosmology proposes that for every big bang there is a big
crunch.
3.
Theories for the origin of the universe must conform to the red shift.
4.
Banded iron formations that show alterations of rusty-red and gray bands indicate
abundant free oxygen in the environment.
5.
Komatiites are ultramafic rocks that reflect the higher-temperature gradients that
prevailed during the Hadean.
6.
Prokaryotes were organisms with a definite nuclear wall, well-defined chromosomes,
and the capacity for sexual reproduction.
7.
The process of accumulating bits of matter around an initial mass is called accretion.
8.
The darker areas that are seen on the moon are called lunar highlands.
9.
Photochemical dissociation is the process by which water vapor and other gases are
released from rocks.
10.
Autotrophs can’t make their own food so they scavenge nutrients in their environment.
Chapter 8—Earliest Earth: 2,100,000,000 Years of the Archean Eon
ANSWER KEY
Multiple Choice
1. d
2. a
3. c
4. d
5. d
6. b
7. b
8. c
9. c
10. a
11. b
12. c
13. a
14. d
15. c
16. a
17. c
18. b
19. b
20. b
Fill Ins
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
platforms
felsic
Komatiites
Kenoran Orogeny
red shift
granulite association
greenstone association
granulite association
greenstone belt
autotroph
cyanobacteria
eukaryote
stromatolite
nebular hypothesis
core, mantel, crust
True/False
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
F
T
T
T
T
F
F
F
F
F
Chapter 8—Earliest Earth: 2,100,000,000 Years of the Archean Eon
RESPONSES TO QUESTIONS ACCOMPANYING SELECTED FIGURES
FIGURE 8–3 (p. 209) From above, the Milky Way galaxy would resemble a discoidal spiral consisting of
stars, planets, satellites, meteors, comets, gases, and dust.
FIGURE 8–12 (p. 216) Escaping gases were responsible for the spherical holes in the lunar basalt. This
indicates a relative, rapid cooling of this rock.
FIGURE 8–27 (p. 227) Both shield and platform are components of the craton. Platforms are regions of
the craton in which igneous and metamorphic basement rocks are covered by a blanket of sedimentary
rocks.