TF阅读真题第918篇Dating Archaeological Objects

Dating Archaeological Objects

 

 

For contemporary archaeologists who need to know the age of any objects they study, perhaps the most precise and yet technologically simple form of dating is dendrochronology-the use of sequences of tree rings to infer time. Most trees add a single ring each year to their circumference, thus, if we count the number of rings, the age of a tree can be precisely established. Normally the tree grows faster in wet years than in dry ones, so the rings found in wet years are wider than the rings found in dry years: therefore, over the centuries there is a unique series of changes in ring widths, and precise dates can be inferred by comparing cross sections taken from trees that overlapped in time. By comparing wooden beams, posts and other objects to cross sections taken from trees that live for long periods, it is often possible to determine the exact year in which the tree used to make the artifact was cut, and that can be used to date the object. However, in dry climates tree trunks cut as lumber tend to be used and reused for very long times, so that the date that the tree actually was cut may be centuries earlier than the period it was used as a beam in some house. Also, since local climates vary, dendrochronological records must be amassed for each region, and at present, detailed records are only available for the North American West, Europe, and the Near East.

The most widely used dating technique is 14C (carbon-14 or radiocarbon dating), a method first outlined in the 1940s by Nobel laureate Willard Libby. When solar radiation strikes the upper atmosphere, it converts a small amount of atmospheric nitrogen into the isotope 14C, a radioactive variant of the element carbon. Wind and other factors spread this 14C throughout the atmosphere, and because all living organisms exchange gases with the atmosphere, the ratio of 14C in their cells is equal to that in the atmosphere. When the organism dies, the 14C trapped in its cells begins to revert to nitrogen, This disintegration (the process of decomposing into other elements) occurs because 14C is unstable, Because we know that approximately half of any given quantity of 14C will disintegrate in about 5,730 years, we can estimate the time an organism has been dead by measuring the amount of 14C against the stable isotopes 12C and 13c remaining in its cells. After about 50,000 years, too little persists to be measurable with standard laboratory methods, although with large samples and the most powerful equipment,reliable dates up to 100,000 years ago are theoretically possible. Radiocarbon dating works best on wood and charcoal, but paper, leather, bone, skin, peat, and many other organic materials can also be dated by this method. Grains and grasses make excellent archaeological samples when charred by fire because they preserve well and are short-lived compared to trees.

The ratio of 14C in the atmosphere has not been constant over the last 50,000 years, and thus 14C dates have had to be corrected by measuring the ratio of 14C in tree rings dated through dendrochronology. Fortunately, some trees such as the bristlecone pine of the western United States, live thousands of years. This makes it feasible to cut pieces from their trunks that can be removed to study their rings over periods of time, and then each ring can be radiocarbon-dated to construct a correction curve. Logs found submerged in northern European wetlands, where they have been preserved for thousands of years, have recently allowed the calculation of a radiocarbon correction curve extending7,000 years for that area But samples dated by the 14C method can still be contaminated with younger or older carbon sources such as groundwater or petroleum deposits. Additionally, we also know that the amount of 14C is not the same for all environments, The Northern and Southern Hemispheres, for example, have different proportions of 14C, These types of factors must be considered or accounted for by the laboratories that process samples for 14C dating. A major advance in radiocarbon dating was made in the 1970s when various researchers used particle accelerators to date samples. This method allows reliable dates to be obtained from samples the size of a match head, whereas older methods require about a handful of carbon.

 

 

题目：

 

 

 

1

For contemporary archaeologists who need to know the age of any objects they study, perhaps the most precise and yet technologically simple form of dating is dendrochronology-the use of sequences of tree rings to infer time. Most trees add a single ring each year to their circumference, thus, if we count the number of rings, the age of a tree can be precisely established. Normally the tree grows faster in wet years than in dry ones, so the rings found in wet years are wider than the rings found in dry years: therefore, over the centuries there is a unique series of changes in ring widths, and precise dates can be inferred by comparing cross sections taken from trees that overlapped in time. By comparing wooden beams, posts and other objects to cross sections taken from trees that live for long periods, it is often possible to determine the exact year in which the tree used to make the artifact was cut, and that can be used to date the object. However, in dry climates tree trunks cut as lumber tend to be used and reused for very long times, so that the date that the tree actually was cut may be centuries earlier than the period it was used as a beam in some house. Also, since local climates vary, dendrochronological records must be amassed for each region, and at present, detailed records are only available for the North American West, Europe, and the Near East.

The word “contemporary” in the passage is closest in meaning to

 

Vocabulary Questions词汇题

 

Acertain

Bpresent-day

Cspecialized

Dpracticing

2

For contemporary archaeologists who need to know the age of any objects they study, perhaps the most precise and yet technologically simple form of dating is dendrochronology-the use of sequences of tree rings to infer time. Most trees add a single ring each year to their circumference, thus, if we count the number of rings, the age of a tree can be precisely established. Normally the tree grows faster in wet years than in dry ones, so the rings found in wet years are wider than the rings found in dry years: therefore, over the centuries there is a unique series of changes in ring widths, and precise dates can be inferred by comparing cross sections taken from trees that overlapped in time. By comparing wooden beams, posts and other objects to cross sections taken from trees that live for long periods, it is often possible to determine the exact year in which the tree used to make the artifact was cut, and that can be used to date the object. However, in dry climates tree trunks cut as lumber tend to be used and reused for very long times, so that the date that the tree actually was cut may be centuries earlier than the period it was used as a beam in some house. Also, since local climates vary, dendrochronological records must be amassed for each region, and at present, detailed records are only available for the North American West, Europe, and the Near East.

The word “amassed” meaning to

 

Vocabulary Questions词汇题

 

Acollected

Bexamined

Cconfirmed

Dadjusted

3

For contemporary archaeologists who need to know the age of any objects they study, perhaps the most precise and yet technologically simple form of dating is dendrochronology-the use of sequences of tree rings to infer time. Most trees add a single ring each year to their circumference, thus, if we count the number of rings, the age of a tree can be precisely established. Normally the tree grows faster in wet years than in dry ones, so the rings found in wet years are wider than the rings found in dry years: therefore, over the centuries there is a unique series of changes in ring widths, and precise dates can be inferred by comparing cross sections taken from trees that overlapped in time. By comparing wooden beams, posts and other objects to cross sections taken from trees that live for long periods, it is often possible to determine the exact year in which the tree used to make the artifact was cut, and that can be used to date the object. However, in dry climates tree trunks cut as lumber tend to be used and reused for very long times, so that the date that the tree actually was cut may be centuries earlier than the period it was used as a beam in some house. Also, since local climates vary, dendrochronological records must be amassed for each region, and at present, detailed records are only available for the North American West, Europe, and the Near East.

According to paragraph 1, all of the following are properties of tree rings that make them useful for dating EXCEPT

 

Negative Factual Information Questions否定事实信息题

 

ATrees living at the same time display similar changes in ring width.

BThe width of the rings changes depending on annual rainfall.

CThe rings are added at regular time intervals.

DThe space between rings becomes smaller as the tree grows older.

4

For contemporary archaeologists who need to know the age of any objects they study, perhaps the most precise and yet technologically simple form of dating is dendrochronology-the use of sequences of tree rings to infer time. Most trees add a single ring each year to their circumference, thus, if we count the number of rings, the age of a tree can be precisely established. Normally the tree grows faster in wet years than in dry ones, so the rings found in wet years are wider than the rings found in dry years: therefore, over the centuries there is a unique series of changes in ring widths, and precise dates can be inferred by comparing cross sections taken from trees that overlapped in time. By comparing wooden beams, posts and other objects to cross sections taken from trees that live for long periods, it is often possible to determine the exact year in which the tree used to make the artifact was cut, and that can be used to date the object. However, in dry climates tree trunks cut as lumber tend to be used and reused for very long times, so that the date that the tree actually was cut may be centuries earlier than the period it was used as a beam in some house. Also, since local climates vary, dendrochronological records must be amassed for each region, and at present, detailed records are only available for the North American West, Europe, and the Near East.

Which TWO of the following are mentioned in paragraph 1 as problems associated with using dendrochronology to date objects? To receive credit, you must select TWO answer choices.

 

Factual Information Questions事实信息题

 

Select 2 answers

ADendrochronology is not always precise because an object may have been made many years after the tree used to make it was cut.

BDendrochronology is only accurate in parts of the world where detailed tree records exist.

CDendrochronology does not always work well in areas where weather varies greatly from year to year

DDendrochronology is less accurate in areas with abundant annual rainfall.

5

The most widely used dating technique is 14C (carbon-14 or radiocarbon dating), a method first outlined in the 1940s by Nobel laureate Willard Libby. When solar radiation strikes the upper atmosphere, it converts a small amount of atmospheric nitrogen into the isotope 14C, a radioactive variant of the element carbon. Wind and other factors spread this 14C throughout the atmosphere, and because all living organisms exchange gases with the atmosphere, the ratio of 14C in their cells is equal to that in the atmosphere. When the organism dies, the 14C trapped in its cells begins to revert to nitrogen, This disintegration (the process of decomposing into other elements) occurs because 14C is unstable, Because we know that approximately half of any given quantity of 14C will disintegrate in about 5,730 years, we can estimate the time an organism has been dead by measuring the amount of 14C against the stable isotopes 12C and 13c remaining in its cells. After about 50,000 years, too little persists to be measurable with standard laboratory methods, although with large samples and the most powerful equipment,reliable dates up to 100,000 years ago are theoretically possible. Radiocarbon dating works best on wood and charcoal, but paper, leather, bone, skin, peat, and many other organic materials can also be dated by this method. Grains and grasses make excellent archaeological samples when charred by fire because they preserve well and are short-lived compared to trees.

What can be inferred from paragraph 2 about an archaeological sample from an organism that does not appear to contain any 14C when measured with standard laboratory methods?

 

Inference Questions推理题

 

AThe sample is most likely very large.

BThe sample was most likely measured using the most powerful equipment.

CThe sample is most likely 50,000 or more years old.

DThe sample was most likely charred by fire.

6

The most widely used dating technique is 14C (carbon-14 or radiocarbon dating), a method first outlined in the 1940s by Nobel laureate Willard Libby. When solar radiation strikes the upper atmosphere, it converts a small amount of atmospheric nitrogen into the isotope 14C, a radioactive variant of the element carbon. Wind and other factors spread this 14C throughout the atmosphere, and because all living organisms exchange gases with the atmosphere, the ratio of 14C in their cells is equal to that in the atmosphere. When the organism dies, the 14C trapped in its cells begins to revert to nitrogen, This disintegration (the process of decomposing into other elements) occurs because 14C is unstable, Because we know that approximately half of any given quantity of 14C will disintegrate in about 5,730 years, we can estimate the time an organism has been dead by measuring the amount of 14C against the stable isotopes 12C and 13c remaining in its cells. After about 50,000 years, too little persists to be measurable with standard laboratory methods, although with large samples and the most powerful equipment,reliable dates up to 100,000 years ago are theoretically possible. Radiocarbon dating works best on wood and charcoal, but paper, leather, bone, skin, peat, and many other organic materials can also be dated by this method. Grains and grasses make excellent archaeological samples when charred by fire because they preserve well and are short-lived compared to trees.

Paragraph 2 supports all of the following about the radiocarbon dating of materials EXCEPT:

 

Negative Factual Information Questions否定事实信息题

 

AIt can be used on a variety of materials

Bit is more accurate for dating such organic materials as paper,leather, bone, skin, and peat because they preserve well.

Cit works especially well on wood and charcoal.

Dit is effective on samples that have been exposed to fire and are short-ived.

7

The ratio of 14C in the atmosphere has not been constant over the last 50,000 years, and thus 14C dates have had to be corrected by measuring the ratio of 14C in tree rings dated through dendrochronology. Fortunately, some trees such as the bristlecone pine of the western United States, live thousands of years. This makes it feasible to cut pieces from their trunks that can be removed to study their rings over periods of time, and then each ring can be radiocarbon-dated to construct a correction curve. Logs found submerged in northern European wetlands, where they have been preserved for thousands of years, have recently allowed the calculation of a radiocarbon correction curve extending7,000 years for that area But samples dated by the 14C method can still be contaminated with younger or older carbon sources such as groundwater or petroleum deposits. Additionally, we also know that the amount of 14C is not the same for all environments, The Northern and Southern Hemispheres, for example, have different proportions of 14C, These types of factors must be considered or accounted for by the laboratories that process samples for 14C dating. A major advance in radiocarbon dating was made in the 1970s when various researchers used particle accelerators to date samples. This method allows reliable dates to be obtained from samples the size of a match head, whereas older methods require about a handful of carbon.

What is the author’s purpose in mentioning that “dated by the 14C method can still be contaminated with younger or older carbon sources such as groundwater or petroleum deposits.?

 

Rhetorical Purpose Questions修辞目的题

 

ATo introduce the idea that atmospheric 14C is not the same for all environments

BTo emphasize the importance of using very old or very well-preserved samples

CTo illustrate the dangers of using samples that have been preserved underwater

DTo identify factors that may make radiocarbon dating less reliable

8

The ratio of 14C in the atmosphere has not been constant over the last 50,000 years, and thus 14C dates have had to be corrected by measuring the ratio of 14C in tree rings dated through dendrochronology. Fortunately, some trees such as the bristlecone pine of the western United States, live thousands of years. This makes it feasible to cut pieces from their trunks that can be removed to study their rings over periods of time, and then each ring can be radiocarbon-dated to construct a correction curve. Logs found submerged in northern European wetlands, where they have been preserved for thousands of years, have recently allowed the calculation of a radiocarbon correction curve extending7,000 years for that area But samples dated by the 14C method can still be contaminated with younger or older carbon sources such as groundwater or petroleum deposits. Additionally, we also know that the amount of 14C is not the same for all environments, The Northern and Southern Hemispheres, for example, have different proportions of 14C, These types of factors must be considered or accounted for by the laboratories that process samples for 14C dating. A major advance in radiocarbon dating was made in the 1970s when various researchers used particle accelerators to date samples. This method allows reliable dates to be obtained from samples the size of a match head, whereas older methods require about a handful of carbon.

According to paragraph 3, the development of particle accelerators in the 1970s allowed researchers to

 

Rhetorical Purpose Questions修辞目的题

 

Adate smaller samples than was previously possible

Bdate samples more quickly than they could in the past

Cdate samples from both the Northern and Southern Hemispheres

Ddate contaminated samples more accurately

9

For contemporary archaeologists who need to know the age of any objects they study, perhaps the most precise and yet technologically simple form of dating is dendrochronology-the use of sequences of tree rings to infer time. [■] Most trees add a single ring each year to their circumference, thus, if we count the number of rings, the age of a tree can be precisely established. [■] Normally the tree grows faster in wet years than in dry ones, so the rings found in wet years are wider than the rings found in dry years: therefore, over the centuries there is a unique series of changes in ring widths, and precise dates can be inferred by comparing cross sections taken from trees that overlapped in time. [■] By comparing wooden beams, posts and other objects to cross sections taken from trees that live for long periods, it is often possible to determine the exact year in which the tree used to make the artifact was cut, and that can be used to date the object. [■] However, in dry climates tree trunks cut as lumber tend to be used and reused for very long times, so that the date that the tree actually was cut may be centuries earlier than the period it was used as a beam in some house. Also, since local climates vary, dendrochronological records must be amassed for each region, and at present, detailed records are only available for the North American West, Europe, and the Near East.

Look at the four squares [■]  that indicate where the following sentence could be added to the passage

These unique properties of trees help archaeologists date a variety of items made from wood.

Insert Text Questions句子插入题

 

Where would the sentence best fit？Click on a square  sentence to the passage.

10

Many archaeological objects can now be dated with great accuracy using two different techniques.

 

Prose Summary Questions概要小结题

 

Select 3 answers

ASome trees add a new ring each year but others add rings more or less often, so cross sections from many trees are needed to create an accurate dendrochronological record.

BIn areas for which detailed dendrochronological records exist. objects made of wood can be dated by comparing them to samples from long-living trees.

CRadiocarbon dating is possible because all organisms living in the same area at the same time contain the same ratio of 14C, and all 14C disintegrates at a constant rate once the organism dies

DExamining, the rings of very old trees can improve the precision of radiocarbon dating because tree rings provide a record of how 14C in the atmosphere varies over time.

ERadiocarbon dating, developed in the 1940s, was not widely used until the 1970s when tools were developed to remove contamination from the carbon in preserved organic materials

FWith the development of particle accelerators and other new technologies, the centuries-old methods of dendrochronology have become largely unnecessary.