TOEFL-3

h4 Dissatisfaction with conventional explanations for dinosaur extinctions led to a surprising
observation that, in turn, has suggested a new hypothesis. Many plants and animals disappearere!
abruptly from the fossil record as one moves from layers of rock documenting the end of the
Cretaceous up into rocks representing the beginning of the Cenozoic (the era after the
Mesozoic). Between the last layer of Cretaceous rock and the first layer of Cenozoic rock,
there is often a thin layer of clay. Scientists felt that they could get an idea of how long the
extinctions took by determining how long it took to deposit this one centimeter of clay and
they thought they could determine the time it took to deposit the clay by determining the
amount of the element iridium (Ir) it contained.

5 Ir has not been common at Earth’s surface since the very beginning of the planet’s history.
Because it usually exists in a metallic state, it was preferentially incorporated in Earth’s core
as the planet cooled and consolidated. Ir is found in high concentrations in some meteorites, in
which the solar system’s original chemical composition is preserved. Even today, microscopic
meteorites continually bombard Earth, falling on both land and sea. By measuring how many
of these meteorites fall to Earth over a given period of time, scientists can estimate how long
it might have taken to deposit the observed amount of Ir in the boundary clay. These
calculations suggest that a period of about one million years would have been required.
However, other reliable evidence suggests that the deposition of the boundary clay could not
have taken one million years. So the unusually high concentration of Ir seems to require a
special explanation

5 Ir has not been common at Earth’s surface since the very beginning of the planet’s history.
Because it usually exists in a metallic state, it was preferentially incorporated in Earth’s core
as the planet cooled and consolidated. Ir is found in high concentrations in some meteorites, in
which the solar system’s original chemical composition is preserved. Even today, microscopic
meteorites continually bombard Earth, falling on both land and sea. By measuring how many
of these meteorites fall to Earth over a given period of time, scientists can estimate how long
it might have taken to deposit the observed amount of Ir in the boundary clay. These
calculations suggest that a period of about one million years would have been required.
However, other reliable evidence suggests that the deposition of the boundary clay could not
have taken one million years. So the unusually high concentration of Ir seems to require a
special explanation.

1 The city of Teotihuacán, which lay about 50 kilometers northeast of modern-day Mexico City,
began its growth by 200 –100 B.C. At its height, between about A.D. 150 and 700, it probably
had a population of more than 125,000 people and covered at least 20 square kilometers. It
had over 2,000 apartment complexes, a great market, a large number of industrial workshops,
an administrative center, a number of massive religious edifices, and a regular grid pattern of
streets and buildings. Clearly, much planning and central control were involved in the
expansion and ordering of this great metropolis. Moreover, the city had economic and perhaps
religious contacts with most parts of Mesoamerica (modern Central America and Mexico).

2 How did this tremendous development take place, and why did it happen in the Teotihuacán
Valley? Among the main factors are Teotihuacán’s geographic location on a natural trade
route to the south and east of the Valley of Mexico, the obsidian1
resources in the Teotihuacán
Valley itself, and the valley’s potential for extensive irrigation. The exact role of other factors
is much more difficult to pinpoint —for instance, Teotihuacán’s religious significance as a
shrine, the historical situation in and around the Valley of Mexico toward the end of the first
millennium B.C., the ingenuity and foresightedness of Teotihuacán’s elite, and, finally, the
impact of natural disasters, such as the volcanic eruptions of the late first millennium B.C

2 How did this tremendous development take place, and why did it happen in the Teotihuacán
Valley? Among the main factors are Teotihuacán’s geographic location on a natural trade
route to the south and east of the Valley of Mexico, the obsidian1
resources in the Teotihuacán
Valley itself, and the valley’s potential for extensive irrigation. The exact role of other factors
is much more difficult to pinpoint —for instance, Teotihuacán’s religious significance as a
shrine, the historical situation in and around the Valley of Mexico toward the end of the first
millennium B.C., the ingenuity and foresightedness of Teotihuacán’s elite, and, finally, the
impact of natural disasters, such as the volcanic eruptions of the late first millennium B.C

3 This last factor is at least circumstantially implicated in Teotihuacán’s rise. Prior to 200 B.C.,
a number of relatively small centers coexisted in and near the Valley of Mexico. Around this
time, the largest of these centers, Cuicuilco, was seriously affected by a volcanic eruption,
with much of its agricultural land covered by lava. With Cuicuilco eliminated as a potential
rival, any one of a number of relatively modest towns might have emerged as a leading
economic and political power in Central Mexico. The archaeological evidence clearly
indicates, though, that Teotihuacán was the center that did arise as the predominant force in
the area by the first century A.D.

4 It seems likely that Teotihuacán’s natural resources—along with the city elite’s ability to
recognize their potential—gave the city a competitive edge over its neighbors. The valley, like
many other places in Mexican and Guatemalan highlands, was rich in obsidian. The hard
volcanic stone was a resource that had been in great demand for many years, at least since the
rise of the Olmecs (a people who flourished between 1200 and 400 B.C.), and it apparently
had a secure market. Moreover, recent research on obsidian tools found at Olmec sites has
shown that some of the obsidian obtained by the Olmecs originated near Teotihuacán.
Teotihuacán obsidian must have been recognized as a valuable commodity for many centuries
before the great city arose.

5 Long-distance trade in obsidian probably gave the elite residents of Teotihuacán access to a
wide variety of exotic goods, as well as a relatively prosperous life. Such success may have
attracted immigrants to Teotihuacán. In addition, Teotihuacán’s elite may have consciously
attempted to attract new inhabitants. It is also probable that as early as 200 B.C. Teotihuacán
may have achieved some religious significance and its shrine (or shrines) may have served as
an additional population magnet. Finally, the growing population was probably fed by
increasing the number and size of irrigated fields.

6 The picture of Teotihuacán that emerges is a classic picture of positive feedback among
obsidian mining and working, trade, population growth, irrigation, and religious tourism. The
thriving obsidian operation, for example, would necessitate more miners, additional
manufacturers of obsidian tools, and additional traders to carry the goods to new markets. All
this led to increased wealth, which in turn would attract more immigrants to Teotihuacán. The
growing power of the elite, who controlled the economy, would give them the means to
physically coerce people to move to Teotihuacán and serve as additions to the labor force.
More irrigation works would have to be built to feed the growing population, and this resulted
in more power and wealth for the elite.

1 There is a quality of cohesiveness about the Roman world that applied neither to
Greece nor perhaps to any other civilization, ancient or modern. Like the stones of a
Roman wall, which were held together both by the regularity of the design and by
that peculiarly powerful Roman cement, so the various parts of the Roman realm
were bonded into a massive, monolithic entity by physical, organizational, and
psychological controls. The physical bonds included the network of military garrisons,
which were stationed in every province, and the network of stone-built roads that
linked the provinces with Rome. The organizational bonds were based on the common
principles of law and administration and on the universal army of officials who enforced
common standards of conduct. The psychological controls were built on fear and
punishment—on the absolute certainty that anyone or anything that threatened the
authority of Rome would be utterly destroyed.
2 The source of the Roman obsession with unity and cohesion may well have lain in
the pattern of Rome’s early development. Whereas Greece had grown from scores
of scattered cities, Rome grew from one single organism. While the Greek world had
expanded along the Mediterranean sea lanes, the Roman world was assembled
by territorial conquest. Of course, the contrast is not quite so stark: in Alexander
the Great the Greeks had found the greatest territorial conqueror of all time; and
the Romans, once they moved outside Italy, did not fail to learn the lessons of sea
power. Yet the essential difference is undeniable. The key to the Greek world lay in its
high-powered ships; the key to Roman power lay in its marching legions. The Greeks
were wedded to the sea; the Romans, to the land. The Greek was a sailor at heart;
the Roman, a landsman.
3 Certainly, in trying to explain the Roman phenomenon, one would have to place great
emphasis on this almost animal instinct for the territorial imperative. Roman priorities
lay in the organization, exploitation, and defense of their territory. In all probability it was
the fertile plain of Latium, where the Latins who founded Rome originated, that created
the habits and skills of landed settlement, landed property, landed economy, landed
administration, and a land-based society. From this arose the Roman genius for military
organization and orderly government. In turn, a deep attachment to the land, and to
the stability which rural life engenders, fostered the Roman virtues: gravitas, a sense of
responsibility, peitas, a sense of devotion to family and country, and iustitia, a sense of
the natural order.
4 Modern attitudes to Roman civilization range from the infinitely impressed to the
thoroughly disgusted. As always, there are the power worshippers, especially among
historians, who are predisposed to admire whatever is strong, who feel more attracted
to the might of Rome than to the subtlety of Greece. At the same time, there is a solid
body of opinion that dislikes Rome. For many, Rome is at best the imitator and the
continuator of Greece on a larger scale. Greek civilization had quality; Rome, mere quantity. Greece was original; Rome, derivative. Greece had style; Rome had money.
Greece was the inventor; Rome, the research and development division. Such indeed
was the opinion of some of the more intellectual Romans. “Had the Greeks held
novelty in such disdain as we,” asked Horace in his Epistles, “what work of ancient
date would now exist?”
5 Rome’s debt to Greece was enormous. The Romans adopted Greek religion and
moral philosophy. In literature, Greek writers were consciously used as models by
their Latin successors. It was absolutely accepted that an educated Roman should
be fluent in Greek. In speculative philosophy and the sciences, the Romans made
virtually no advance on early achievements.
6 Yet it would be wrong to suggest that Rome was somehow a junior partner in GrecoRoman civilization. The Roman genius was projected into new spheres—especially
into those of law, military organization, administration, and engineering. Moreover, the
tensions that arose within the Roman state produced literary and artistic sensibilities
of the highest order. It was no accident that many leading Roman soldiers and
statesmen were writers of high caliber.

1. There is a quality of cohesiveness about the Roman world that applied neither to
Greece nor perhaps to any other civilization, ancient or modern. Like the stones of a
Roman wall, which were held together both by the regularity of the design and by
that peculiarly powerful Roman cement, so the various parts of the Roman realm
were bonded into a massive, monolithic entity by physical, organizational, and
psychological controls. The physical bonds included the network of military garrisons,
which were stationed in every province, and the network of stone-built roads that
linked the provinces with Rome. The organizational bonds were based on the common
principles of law and administration and on the universal army of officials who enforced
common standards of conduct. The psychological controls were built on fear and
punishment—on the absolute certainty that anyone or anything that threatened the
authority of Rome would be utterly destroyed.

2 The source of the Roman obsession with unity and cohesion may well have lain in
the pattern of Rome’s early development. Whereas Greece had grown from scores
of scattered cities, Rome grew from one single organism. While the Greek world had
expanded along the Mediterranean sea lanes, the Roman world was assembled
by territorial conquest. Of course, the contrast is not quite so stark: in Alexander
the Great the Greeks had found the greatest territorial conqueror of all time; and
the Romans, once they moved outside Italy, did not fail to learn the lessons of sea
power. Yet the essential difference is undeniable. The key to the Greek world lay in its
high-powered ships; the key to Roman power lay in its marching legions. The Greeks
were wedded to the sea; the Romans, to the land. The Greek was a sailor at heart;
the Roman, a landsman.

1 There is a quality of cohesiveness about the Roman world that applied neither to
Greece nor perhaps to any other civilization, ancient or modern. Like the stones of a
Roman wall, which were held together both by the regularity of the design and by
that peculiarly powerful Roman cement, so the various parts of the Roman realm
were bonded into a massive, monolithic entity by physical, organizational, and
psychological controls. The physical bonds included the network of military garrisons,
which were stationed in every province, and the network of stone-built roads that
linked the provinces with Rome. The organizational bonds were based on the common
principles of law and administration and on the universal army of officials who enforced
common standards of conduct. The psychological controls were built on fear and
punishment—on the absolute certainty that anyone or anything that threatened the
authority of Rome would be utterly destroyed.
2 The source of the Roman obsession with unity and cohesion may well have lain in
the pattern of Rome’s early development. Whereas Greece had grown from scores
of scattered cities, Rome grew from one single organism. While the Greek world had
expanded along the Mediterranean sea lanes, the Roman world was assembled
by territorial conquest. Of course, the contrast is not quite so stark: in Alexander
the Great the Greeks had found the greatest territorial conqueror of all time; and
the Romans, once they moved outside Italy, did not fail to learn the lessons of sea
power. Yet the essential difference is undeniable. The key to the Greek world lay in its
high-powered ships; the key to Roman power lay in its marching legions. The Greeks
were wedded to the sea; the Romans, to the land. The Greek was a sailor at heart;
the Roman, a landsman.
3 Certainly, in trying to explain the Roman phenomenon, one would have to place great
emphasis on this almost animal instinct for the territorial imperative. Roman priorities
lay in the organization, exploitation, and defense of their territory. In all probability it was
the fertile plain of Latium, where the Latins who founded Rome originated, that created
the habits and skills of landed settlement, landed property, landed economy, landed
administration, and a land-based society. From this arose the Roman genius for military
organization and orderly government. In turn, a deep attachment to the land, and to
the stability which rural life engenders, fostered the Roman virtues: gravitas, a sense of
responsibility, peitas, a sense of devotion to family and country, and iustitia, a sense of
the natural order.
4 Modern attitudes to Roman civilization range from the infinitely impressed to the
thoroughly disgusted. As always, there are the power worshippers, especially among
historians, who are predisposed to admire whatever is strong, who feel more attracted
to the might of Rome than to the subtlety of Greece. At the same time, there is a solid
body of opinion that dislikes Rome. For many, Rome is at best the imitator and the
continuator of Greece on a larger scale. Greek civilization had quality; Rome, mere quantity. Greece was original; Rome, derivative. Greece had style; Rome had money.
Greece was the inventor; Rome, the research and development division. Such indeed
was the opinion of some of the more intellectual Romans. “Had the Greeks held
novelty in such disdain as we,” asked Horace in his Epistles, “what work of ancient
date would now exist?”
5 Rome’s debt to Greece was enormous. The Romans adopted Greek religion and
moral philosophy. In literature, Greek writers were consciously used as models by
their Latin successors. It was absolutely accepted that an educated Roman should
be fluent in Greek. In speculative philosophy and the sciences, the Romans made
virtually no advance on early achievements.
6 Yet it would be wrong to suggest that Rome was somehow a junior partner in GrecoRoman civilization. The Roman genius was projected into new spheres—especially
into those of law, military organization, administration, and engineering. Moreover, the
tensions that arose within the Roman state produced literary and artistic sensibilities
of the highest order. It was no accident that many leading Roman soldiers and
statesmen were writers of high caliber.

1 There is a quality of cohesiveness about the Roman world that applied neither to
Greece nor perhaps to any other civilization, ancient or modern. Like the stones of a
Roman wall, which were held together both by the regularity of the design and by
that peculiarly powerful Roman cement, so the various parts of the Roman realm
were bonded into a massive, monolithic entity by physical, organizational, and
psychological controls. The physical bonds included the network of military garrisons,
which were stationed in every province, and the network of stone-built roads that
linked the provinces with Rome. The organizational bonds were based on the common
principles of law and administration and on the universal army of officials who enforced
common standards of conduct. The psychological controls were built on fear and
punishment—on the absolute certainty that anyone or anything that threatened the
authority of Rome would be utterly destroyed.
2 The source of the Roman obsession with unity and cohesion may well have lain in
the pattern of Rome’s early development. Whereas Greece had grown from scores
of scattered cities, Rome grew from one single organism. While the Greek world had
expanded along the Mediterranean sea lanes, the Roman world was assembled
by territorial conquest. Of course, the contrast is not quite so stark: in Alexander
the Great the Greeks had found the greatest territorial conqueror of all time; and
the Romans, once they moved outside Italy, did not fail to learn the lessons of sea
power. Yet the essential difference is undeniable. The key to the Greek world lay in its
high-powered ships; the key to Roman power lay in its marching legions. The Greeks
were wedded to the sea; the Romans, to the land. The Greek was a sailor at heart;
the Roman, a landsman.
3 Certainly, in trying to explain the Roman phenomenon, one would have to place great
emphasis on this almost animal instinct for the territorial imperative. Roman priorities
lay in the organization, exploitation, and defense of their territory. In all probability it was
the fertile plain of Latium, where the Latins who founded Rome originated, that created
the habits and skills of landed settlement, landed property, landed economy, landed
administration, and a land-based society. From this arose the Roman genius for military
organization and orderly government. In turn, a deep attachment to the land, and to
the stability which rural life engenders, fostered the Roman virtues: gravitas, a sense of
responsibility, peitas, a sense of devotion to family and country, and iustitia, a sense of
the natural order.
4 Modern attitudes to Roman civilization range from the infinitely impressed to the
thoroughly disgusted. As always, there are the power worshippers, especially among
historians, who are predisposed to admire whatever is strong, who feel more attracted
to the might of Rome than to the subtlety of Greece. At the same time, there is a solid
body of opinion that dislikes Rome. For many, Rome is at best the imitator and the
continuator of Greece on a larger scale. Greek civilization had quality; Rome, mere quantity. Greece was original; Rome, derivative. Greece had style; Rome had money.
Greece was the inventor; Rome, the research and development division. Such indeed
was the opinion of some of the more intellectual Romans. “Had the Greeks held
novelty in such disdain as we,” asked Horace in his Epistles, “what work of ancient
date would now exist?”
5 Rome’s debt to Greece was enormous. The Romans adopted Greek religion and
moral philosophy. In literature, Greek writers were consciously used as models by
their Latin successors. It was absolutely accepted that an educated Roman should
be fluent in Greek. In speculative philosophy and the sciences, the Romans made
virtually no advance on early achievements.
6 Yet it would be wrong to suggest that Rome was somehow a junior partner in GrecoRoman civilization. The Roman genius was projected into new spheres—especially
into those of law, military organization, administration, and engineering. Moreover, the
tensions that arose within the Roman state produced literary and artistic sensibilities
of the highest order. It was no accident that many leading Roman soldiers and
statesmen were writers of high caliber.

3 Certainly, in trying to explain the Roman phenomenon, one would have to place great
emphasis on this almost animal instinct for the territorial imperative. Roman priorities
lay in the organization, exploitation, and defense of their territory. In all probability it was
the fertile plain of Latium, where the Latins who founded Rome originated, that created
the habits and skills of landed settlement, landed property, landed economy, landed
administration, and a land-based society. From this arose the Roman genius for military
organization and orderly government. In turn, a deep attachment to the land, and to
the stability which rural life engenders, fostered the Roman virtues: gravitas, a sense of
responsibility, peitas, a sense of devotion to family and country, and iustitia, a sense of
the natural order.

4 Modern attitudes to Roman civilization range from the infinitely impressed to the
thoroughly disgusted. As always, there are the power worshippers, especially among
historians, who are predisposed to admire whatever is strong, who feel more attracted
to the might of Rome than to the subtlety of Greece. At the same time, there is a solid
body of opinion that dislikes Rome. For many, Rome is at best the imitator and the
continuator of Greece on a larger scale. Greek civilization had quality; Rome, mere
quantity. Greece was original; Rome, derivative. Greece had style; Rome had money.
Greece was the inventor; Rome, the research and development division. Such indeed
was the opinion of some of the more intellectual Romans. “Had the Greeks held
novelty in such disdain as we,” asked Horace in his Epistles, “what work of ancient
date would now exist?”

4 Modern attitudes to Roman civilization range from the infinitely impressed to the
thoroughly disgusted. As always, there are the power worshippers, especially among
historians, who are predisposed to admire whatever is strong, who feel more attracted
to the might of Rome than to the subtlety of Greece. At the same time, there is a solid
body of opinion that dislikes Rome. For many, Rome is at best the imitator and the
continuator of Greece on a larger scale. Greek civilization had quality; Rome, mere quantity. Greece was original; Rome, derivative. Greece had style; Rome had money.
Greece was the inventor; Rome, the research and development division. Such indeed
was the opinion of some of the more intellectual Romans. “Had the Greeks held
novelty in such disdain as we,” asked Horace in his Epistles, “what work of ancient
date would now exist?”

4 Modern attitudes to Roman civilization range from the infinitely impressed to the
thoroughly disgusted. As always, there are the power worshippers, especially among
historians, who are predisposed to admire whatever is strong, who feel more attracted
to the might of Rome than to the subtlety of Greece. At the same time, there is a solid
body of opinion that dislikes Rome. For many, Rome is at best the imitator and the
continuator of Greece on a larger scale. Greek civilization had quality; Rome, mere quantity. Greece was original; Rome, derivative. Greece had style; Rome had money.
Greece was the inventor; Rome, the research and development division. Such indeed
was the opinion of some of the more intellectual Romans. “Had the Greeks held
novelty in such disdain as we,” asked Horace in his Epistles, “what work of ancient
date would now exist?”

6 Yet it would be wrong to suggest that Rome was somehow a junior partner in GrecoRoman civilization. The Roman genius was projected into new spheres—especially
into those of law, military organization, administration, and engineering. Moreover, the
tensions that arose within the Roman state produced literary and artistic sensibilities
of the highest order. It was no accident that many leading Roman soldiers and
statesmen were writers of high caliber.

1 In 1970 geologists Kenneth J. Hsu and William B. F. Ryan were collecting research data
while aboard the oceanographic research vessel Glomar Challenger. An objective of this
particular cruise was to investigate the floor of the Mediterranean and to resolve questions
about its geologic history. One question was related to evidence that the invertebrate fauna
(animals without spines) of the Mediterranean had changed abruptly about 6 million years
ago. Most of the older organisms were nearly wiped out, although a few hardy species
survived. A few managed to migrate into the Atlantic. Somewhat later, the migrants returned,
bringing new species with them. Why did the near extinction and migrations occur?

3 With questions such as these clearly before them, the scientists aboard the Glomar Challenger
proceeded to the Mediterranean to search for the answers. On August 23, 1970, they
recovered a sample. The sample consisted of pebbles of hardened sediment that had once been
soft, deep-sea mud, as well as granules of gypsum1
and fragments of volcanic rock. Not a
single pebble was found that might have indicated that the pebbles came from the nearby
continent. In the days following, samples of solid gypsum were repeatedly brought on deck as
drilling operations penetrated the seafloor. Furthermore, the gypsum was found to possess
peculiarities of composition and structure that suggested it had formed on desert flats.
Sediment above and below the gypsum layer contained tiny marine fossils, indicating open
ocean conditions. As they drilled into the central and deepest part of the Mediterranean basin,
the scientists took solid, shiny, crystalline salt from the core barrel. Interbedded with the salt
were thin layers of what appeared to be windblown silt.

3 With questions such as these clearly before them, the scientists aboard the Glomar Challenger
proceeded to the Mediterranean to search for the answers. On August 23, 1970, they
recovered a sample. The sample consisted of pebbles of hardened sediment that had once been
soft, deep-sea mud, as well as granules of gypsum1
and fragments of volcanic rock. Not a
single pebble was found that might have indicated that the pebbles came from the nearby
continent. In the days following, samples of solid gypsum were repeatedly brought on deck as
drilling operations penetrated the seafloor. Furthermore, the gypsum was found to possess
peculiarities of composition and structure that suggested it had formed on desert flats.
Sediment above and below the gypsum layer contained tiny marine fossils, indicating open
ocean conditions. As they drilled into the central and deepest part of the Mediterranean basin,
the scientists took solid, shiny, crystalline salt from the core barrel. Interbedded with the salt
were thin layers of what appeared to be windblown silt.

4 The time had come to formulate a hypothesis. The investigators theorized that about 20
million years ago, the Mediterranean was a broad seaway linked to the Atlantic by two narrow
straits. Crustal movements closed the straits, and the landlocked Mediterranean began to
evaporate. Increasing salinity caused by the evaporation resulted in the extermination of
scores of invertebrate species. Only a few organisms especially tolerant of very salty
conditions remained. As evaporation continued, the remaining brine (salt water) became so
dense that the calcium sulfate of the hard layer was precipitated. In the central deeper part of
the basin, the last of the brine evaporated to precipitate more soluble sodium chloride (salt).
Later, under the weight of overlying sediments, this salt flowed plastically upward to form salt
domes. Before this happened, however, the Mediterranean was a vast desert 3,000 meters
deep. Then, about 5.5 million years ago came the deluge. As a result of crustal adjustments
and faulting, the Strait of Gibraltar, where the Mediterranean now connects to the Atlantic,
opened, and water cascaded spectacularly back into the Mediterranean. Turbulent waters tore
into the hardened salt flats, broke them up, and ground them into the pebbles observed in the
first sample taken by the Challenger. As the basin was refilled, normal marine organisms
returned. Soon layers of oceanic ooze began to accumulate above the old hard layer

4 The time had come to formulate a hypothesis. The investigators theorized that about 20
million years ago, the Mediterranean was a broad seaway linked to the Atlantic by two narrow
straits. Crustal movements closed the straits, and the landlocked Mediterranean began to
evaporate. Increasing salinity caused by the evaporation resulted in the extermination of
scores of invertebrate species. Only a few organisms especially tolerant of very salty
conditions remained. As evaporation continued, the remaining brine (salt water) became so
dense that the calcium sulfate of the hard layer was precipitated. In the central deeper part of
the basin, the last of the brine evaporated to precipitate more soluble sodium chloride (salt).
Later, under the weight of overlying sediments, this salt flowed plastically upward to form salt
domes. Before this happened, however, the Mediterranean was a vast desert 3,000 meters
deep. Then, about 5.5 million years ago came the deluge. As a result of crustal adjustments
and faulting, the Strait of Gibraltar, where the Mediterranean now connects to the Atlantic,
opened, and water cascaded spectacularly back into the Mediterranean. Turbulent waters tore
into the hardened salt flats, broke them up, and ground them into the pebbles observed in the
first sample taken by the Challenger. As the basin was refilled, normal marine organisms
returned. Soon layers of oceanic ooze began to accumulate above the old hard layer.

4 The time had come to formulate a hypothesis. The investigators theorized that about 20
million years ago, the Mediterranean was a broad seaway linked to the Atlantic by two narrow
straits. Crustal movements closed the straits, and the landlocked Mediterranean began to
evaporate. Increasing salinity caused by the evaporation resulted in the extermination of
scores of invertebrate species. Only a few organisms especially tolerant of very salty
conditions remained. As evaporation continued, the remaining brine (salt water) became so
dense that the calcium sulfate of the hard layer was precipitated. In the central deeper part of
the basin, the last of the brine evaporated to precipitate more soluble sodium chloride (salt).
Later, under the weight of overlying sediments, this salt flowed plastically upward to form salt
domes. Before this happened, however, the Mediterranean was a vast desert 3,000 meters
deep. Then, about 5.5 million years ago came the deluge. As a result of crustal adjustments
and faulting, the Strait of Gibraltar, where the Mediterranean now connects to the Atlantic,
opened, and water cascaded spectacularly back into the Mediterranean. Turbulent waters tore
into the hardened salt flats, broke them up, and ground them into the pebbles observed in the
first sample taken by the Challenger. As the basin was refilled, normal marine organisms
returned. Soon layers of oceanic ooze began to accumulate above the old hard layer.

2 Another task for the Glomar Challenger’s scientists was to try to determine the origin of the
domelike masses buried deep beneath the Mediterranean seafloor. These structures had been
detected years earlier by echo-sounding instruments, but they had never been penetrated in the
course of drilling. Were they salt domes such as are common along the United States Gulf
Coast, and if so, why should there have been so much solid crystalline salt beneath the floor of
the Mediterranean?

1 Photographic evidence suggests that liquid water once existed in great quantity
on the surface of Mars. Two types of flow features are seen: runoff channels and
outflow channels. Runoff channels are found in the southern highlands. These flow
features are extensive systems—sometimes hundreds of kilometers in total length—of
interconnecting, twisting channels that seem to merge into larger, wider channels.
They bear a strong resemblance to river systems on Earth, and geologists think that
they are dried-up beds of long-gone rivers that once carried rainfall on Mars from the
mountains down into the valleys. Runoff channels on Mars speak of a time 4 billion
years ago (the age of the Martian highlands), when the atmosphere was thicker, the
surface warmer, and liquid water widespread.

1 Photographic evidence suggests that liquid water once existed in great quantity
on the surface of Mars. Two types of flow features are seen: runoff channels and
outflow channels. Runoff channels are found in the southern highlands. These flow
features are extensive systems—sometimes hundreds of kilometers in total length—of
interconnecting, twisting channels that seem to merge into larger, wider channels.
They bear a strong resemblance to river systems on Earth, and geologists think that
they are dried-up beds of long-gone rivers that once carried rainfall on Mars from the
mountains down into the valleys. Runoff channels on Mars speak of a time 4 billion
years ago (the age of the Martian highlands), when the atmosphere was thicker, the
surface warmer, and liquid water widespread.
2 Outflow channels are probably relics of catastrophic flooding on Mars long ago. They
appear only in equatorial regions and generally do not form extensive interconnected
networks. Instead, they are probably the paths taken by huge volumes of water
draining from the southern highlands into the northern plains. The onrushing water
arising from these flash floods likely also formed the odd teardrop-shaped “islands”
(resembling the miniature versions seen in the wet sand of our beaches at low
tide) that have been found on the plains close to the ends of the outflow channels.
Judging from the width and depth of the channels, the flow rates must have been
truly enormous—perhaps as much as a hundred times greater than the 105 tons
per second carried by the great Amazon river. Flooding shaped the outflow channels
approximately 3 billion years ago, about the same time as the northern volcanic
plains formed.
3 Some scientists speculate that Mars may have enjoyed an extended early period
during which rivers, lakes, and perhaps even oceans adorned its surface. A 2003
Mars Global Surveyor image shows what mission specialists think may be a delta—a
fan-shaped network of channels and sediments where a river once flowed into a
larger body of water, in this case a lake filling a crater in the southern highlands.
Other researchers go even further, suggesting that the data provide evidence for
large open expanses of water on the early Martian surface. A computer-generated
view of the Martian north polar region shows the extent of what may have been an
ancient ocean covering much of the northern lowlands. The Hellas Basin, which
measures some 3,000 kilometers across and has a floor that lies nearly 9 kilometers
below the basin’s rim, is another candidate for an ancient Martian sea.
4 These ideas remain controversial. Proponents point to features such as the terraced
“beaches” shown in one image, which could conceivably have been left behind as a
lake or ocean evaporated and the shoreline receded. But detractors maintain that
the terraces could also have been created by geological activity, perhaps related
to the geologic forces that depressed the Northern Hemisphere far below the
level of the south, in which case they have nothing whatever to do with Martian
water. Furthermore, Mars Global Surveyor data released in 2003 seem to indicate
that the Martian surface contains too few carbonate rock layers—layers containing
compounds of carbon and oxygen—that should have been formed in abundance in
an ancient ocean. Their absence supports the picture of a cold, dry Mars that never
experienced the extended mild period required to form lakes and oceans. However,
more recent data imply that at least some parts of the planet did in fact experience
long periods in the past during which liquid water existed on the surface.
5 Aside from some small-scale gullies (channels) found since 2000, which are
inconclusive, astronomers have no direct evidence for liquid water anywhere on the
surface of Mars today, and the amount of water vapor in the Martian atmosphere is
tiny. Yet even setting aside the unproven hints of ancient oceans, the extent of the
outflow channels suggests that a huge total volume of water existed on Mars in the
past. Where did all the water go? The answer may be that virtually all the water on
Mars is now locked in the permafrost layer under the surface, with more contained in
the planet’s polar caps.

2 Outflow channels are probably relics of catastrophic flooding on Mars long ago. They
appear only in equatorial regions and generally do not form extensive interconnected
networks. Instead, they are probably the paths taken by huge volumes of water
draining from the southern highlands into the northern plains. The onrushing water
arising from these flash floods likely also formed the odd teardrop-shaped “islands”
(resembling the miniature versions seen in the wet sand of our beaches at low
tide) that have been found on the plains close to the ends of the outflow channels.
Judging from the width and depth of the channels, the flow rates must have been
truly enormous—perhaps as much as a hundred times greater than the 105 tons
per second carried by the great Amazon river. Flooding shaped the outflow channels
approximately 3 billion years ago, about the same time as the northern volcanic
plains formed.

2 Outflow channels are probably relics of catastrophic flooding on Mars long ago. They
appear only in equatorial regions and generally do not form extensive interconnected
networks. Instead, they are probably the paths taken by huge volumes of water
draining from the southern highlands into the northern plains. The onrushing water
arising from these flash floods likely also formed the odd teardrop-shaped “islands”
(resembling the miniature versions seen in the wet sand of our beaches at low
tide) that have been found on the plains close to the ends of the outflow channels.
Judging from the width and depth of the channels, the flow rates must have been
truly enormous—perhaps as much as a hundred times greater than the 105 tons
per second carried by the great Amazon river. Flooding shaped the outflow channels
approximately 3 billion years ago, about the same time as the northern volcanic
plains formed.

3 Some scientists speculate that Mars may have enjoyed an extended early period
during which rivers, lakes, and perhaps even oceans adorned its surface. A 2003
Mars Global Surveyor image shows what mission specialists think may be a delta—a
fan-shaped network of channels and sediments where a river once flowed into a
larger body of water, in this case a lake filling a crater in the southern highlands.
Other researchers go even further, suggesting that the data provide evidence for
large open expanses of water on the early Martian surface. A computer-generated
view of the Martian north polar region shows the extent of what may have been an
ancient ocean covering much of the northern lowlands. The Hellas Basin, which
measures some 3,000 kilometers across and has a floor that lies nearly 9 kilometers
below the basin’s rim, is another candidate for an ancient Martian sea

3 Some scientists speculate that Mars may have enjoyed an extended early period
during which rivers, lakes, and perhaps even oceans adorned its surface. A 2003
Mars Global Surveyor image shows what mission specialists think may be a delta—a
fan-shaped network of channels and sediments where a river once flowed into a
larger body of water, in this case a lake filling a crater in the southern highlands.
Other researchers go even further, suggesting that the data provide evidence for
large open expanses of water on the early Martian surface. A computer-generated
view of the Martian north polar region shows the extent of what may have been an
ancient ocean covering much of the northern lowlands. The Hellas Basin, which
measures some 3,000 kilometers across and has a floor that lies nearly 9 kilometers
below the basin’s rim, is another candidate for an ancient Martian sea

3 Some scientists speculate that Mars may have enjoyed an extended early period
during which rivers, lakes, and perhaps even oceans adorned its surface. A 2003
Mars Global Surveyor image shows what mission specialists think may be a delta—a
fan-shaped network of channels and sediments where a river once flowed into a
larger body of water, in this case a lake filling a crater in the southern highlands.
Other researchers go even further, suggesting that the data provide evidence for
large open expanses of water on the early Martian surface. A computer-generated
view of the Martian north polar region shows the extent of what may have been an
ancient ocean covering much of the northern lowlands. The Hellas Basin, which
measures some 3,000 kilometers across and has a floor that lies nearly 9 kilometers
below the basin’s rim, is another candidate for an ancient Martian sea

3 Some scientists speculate that Mars may have enjoyed an extended early period
during which rivers, lakes, and perhaps even oceans adorned its surface. A 2003
Mars Global Surveyor image shows what mission specialists think may be a delta—a
fan-shaped network of channels and sediments where a river once flowed into a
larger body of water, in this case a lake filling a crater in the southern highlands.
Other researchers go even further, suggesting that the data provide evidence for
large open expanses of water on the early Martian surface. A computer-generated
view of the Martian north polar region shows the extent of what may have been an
ancient ocean covering much of the northern lowlands. The Hellas Basin, which
measures some 3,000 kilometers across and has a floor that lies nearly 9 kilometers
below the basin’s rim, is another candidate for an ancient Martian sea

1 Photographic evidence suggests that liquid water once existed in great quantity
on the surface of Mars. Two types of flow features are seen: runoff channels and
outflow channels. Runoff channels are found in the southern highlands. These flow
features are extensive systems—sometimes hundreds of kilometers in total length—of
interconnecting, twisting channels that seem to merge into larger, wider channels.
They bear a strong resemblance to river systems on Earth, and geologists think that
they are dried-up beds of long-gone rivers that once carried rainfall on Mars from the
mountains down into the valleys. Runoff channels on Mars speak of a time 4 billion
years ago (the age of the Martian highlands), when the atmosphere was thicker, the
surface warmer, and liquid water widespread.
2 Outflow channels are probably relics of catastrophic flooding on Mars long ago. They
appear only in equatorial regions and generally do not form extensive interconnected
networks. Instead, they are probably the paths taken by huge volumes of water
draining from the southern highlands into the northern plains. The onrushing water
arising from these flash floods likely also formed the odd teardrop-shaped “islands”
(resembling the miniature versions seen in the wet sand of our beaches at low
tide) that have been found on the plains close to the ends of the outflow channels.
Judging from the width and depth of the channels, the flow rates must have been
truly enormous—perhaps as much as a hundred times greater than the 105 tons
per second carried by the great Amazon river. Flooding shaped the outflow channels
approximately 3 billion years ago, about the same time as the northern volcanic
plains formed.
3 Some scientists speculate that Mars may have enjoyed an extended early period
during which rivers, lakes, and perhaps even oceans adorned its surface. A 2003
Mars Global Surveyor image shows what mission specialists think may be a delta—a
fan-shaped network of channels and sediments where a river once flowed into a
larger body of water, in this case a lake filling a crater in the southern highlands.
Other researchers go even further, suggesting that the data provide evidence for
large open expanses of water on the early Martian surface. A computer-generated
view of the Martian north polar region shows the extent of what may have been an
ancient ocean covering much of the northern lowlands. The Hellas Basin, which
measures some 3,000 kilometers across and has a floor that lies nearly 9 kilometers
below the basin’s rim, is another candidate for an ancient Martian sea.
4 These ideas remain controversial. Proponents point to features such as the terraced
“beaches” shown in one image, which could conceivably have been left behind as a
lake or ocean evaporated and the shoreline receded. But detractors maintain that
the terraces could also have been created by geological activity, perhaps related
to the geologic forces that depressed the Northern Hemisphere far below the
level of the south, in which case they have nothing whatever to do with Martian
water. Furthermore, Mars Global Surveyor data released in 2003 seem to indicate
that the Martian surface contains too few carbonate rock layers—layers containing
compounds of carbon and oxygen—that should have been formed in abundance in
an ancient ocean. Their absence supports the picture of a cold, dry Mars that never
experienced the extended mild period required to form lakes and oceans. However,
more recent data imply that at least some parts of the planet did in fact experience
long periods in the past during which liquid water existed on the surface.
5 Aside from some small-scale gullies (channels) found since 2000, which are
inconclusive, astronomers have no direct evidence for liquid water anywhere on the
surface of Mars today, and the amount of water vapor in the Martian atmosphere is
tiny. Yet even setting aside the unproven hints of ancient oceans, the extent of the
outflow channels suggests that a huge total volume of water existed on Mars in the
past. Where did all the water go? The answer may be that virtually all the water on
Mars is now locked in the permafrost layer under the surface, with more contained in
the planet’s polar caps.

4 These ideas remain controversial. Proponents point to features such as the terraced
“beaches” shown in one image, which could conceivably have been left behind as a
lake or ocean evaporated and the shoreline receded. But detractors maintain that
the terraces could also have been created by geological activity, perhaps related
to the geologic forces that depressed the Northern Hemisphere far below the
level of the south, in which case they have nothing whatever to do with Martian
water. Furthermore, Mars Global Surveyor data released in 2003 seem to indicate
that the Martian surface contains too few carbonate rock layers—layers containing
compounds of carbon and oxygen—that should have been formed in abundance in
an ancient ocean. Their absence supports the picture of a cold, dry Mars that never
experienced the extended mild period required to form lakes and oceans. However,
more recent data imply that at least some parts of the planet did in fact experience
long periods in the past during which liquid water existed on the surface.