Sedimentary rocks are rocks formed by the deposit of sedimen..

更多“Sedimentary rocks are rocks formed by the deposit of sediment as in a river bed.”相关的问题

第1题

Rocks which have solidified directly from molten materials are called igneous rocks. Igneo

us rocks are commonly referred to as primary rocks because they are the original source of material found in sedimentaries and metamorphics. Igneous rocks compose the greater part of the earth's crust, but they are generally covered at the surface by a relatively thin layer of sedimentary or metamorphic rocks. Igneous rocks are distinguished by the following characteristics: (1) they contain no fossils; (2) they have no regular arrangement of layers; and (3) they are nearly always made up of crystals.

Sedimentary rocks are composed largely of minute fragments derived from the disintegration of existing rocks and in some instances from the remains of animals. As sediments are transported, individual fragments are assorted according to size. Distinct layers of such sediments as gravels, sand, and clay build up, as they are deposited by water and occasionally wind. These sediments vary in size with the material and the power of the eroding agent. Sedimentary materials are laid clown in layers called strata.

When sediments harden into sedimentary rocks, the names applied to them change to indicate the change in physical state. Thus, small stones and gravel cemented together are known as conglomerates; cemented sand becomes sandstone; and hardened clay becomes shale. In addition to these, other sedimentary rocks such as limestone frequently result from the deposition of dissolved material. The ingredient parts are normally precipitated by organic substances, such as shells of clams or hard skeletons of other marine life.

Both igneous and sedimentary rocks may be changed by pressure, heat, solution, or cementing action. When individual grains from existing rocks tend to deform. and interlock, they are called metamorphic rocks. For example, granite, an igneous rock, may be metamorphosed into a gneiss or a schist. Limestone, a sedimentary rock, when subjected to heat and pressure may become marble, a metamorphic rock. Shale under pressure becomes slate.

Which one of the following is a metamorphic rock？

A．Granite.

B．Shale.

C．Slate.

D．Limestone.

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第2题

Sedimentary rocks cover much of the Earth’s surface, but they are often hidden by a thin v

eneer of soil.

A．concealed

B．eroded

C．protected

D．softened

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第3题

Hornfelsis a metamorphic rock formed when magma（molten rock) heats sedimentary rocks on Ea

Hornfelsis a metamorphic rock formed when magma(molten rock) heats sedimentary rocks on Earth’s sur-face. According to Figure 1, hornfels is most likely amember of which of the following facies？

A.Facies A

B.Facies C

C.Facies E

D.Facies G

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第4题

According to the passage, outgassing eventually led to all of the following EXCEPT ______.

A．increases in the carbon dioxide content of sedimentary rocks

B．the formation of bodies of water

C．decreases in the level of nitrogen

D．the formation of clouds

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第5题

CIC ICC Prevailing Perils of the sea Ship stranding Striking upon the rocks Sinking Collis

ion Explosion Pilferage Clashing breakage Leakage Dampness Hook damage Rusting Taint of odour Contamination Actual total loss Constructive total loss Particular average General average Sue and labour expenses Salvage charges FPA WPA AR General Additional risks Special additional risks Insurance premium Insured amount

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第6题

Rubidium, potassium and carbon are three common elements used to date the history of Earth

. The rates of radioactive decay of these elements are absolutely regular when averaged out over a period of time; nothing is known to change them. To be useful as clocks, the elements have to be fairly common in natural minerals, unstable but decay slowly over millions of years to form. recognizable "daughter" products which are preserved minerals.

For example, an atom of radioactive rubidium decays to form. an atom of strontium (another element) by converting a neutron in its nucleus to a proton and releasing an electron, generating energy in the process. The radiogenic daughter products of the decay-in this case strontium atoms--diffuse away and are lost above a certain very high temperature. So by measuring the exact proportions of rubidium and strontium atoms that are present in a mineral, researchers can work out how long it has been since the mineral cooled below that critical "blocking" temperature. The main problems with this dating method are the difficulty in finding minerals containing rubidium, the accuracy with which the proportions of rubidium and strontium are measured, and the fact that the method gives only the date when the mineral last cooled below the blocking temperature. Because the blocking temperature is very high, the method is used, mainly for recrystallized (igneous or metamorphic) rocks, not for sediments--rubidium-bearing minerals in sediments simply record the age of cooling of the rocks which were eroded to form. the sediments, not the age of deposition of the sediments themselves.

Potassium decays to form. (a gas) which is sometimes lost from its host mineral by escaping through pores. Although potassium-argon dating is therefore rather unreliable, it can sometimes be useful in dating sedimentary rocks because potassium is common in some minerals which form. in sediments at low temperatures. Assuming no argon has escaped, the potassium-argon date records the age of the sediments themselves.

Carbon dating is mainly used in archaeology. Most carbon atoms (carbon-12) are stable and do not change over time. However, cosmic radiation bombarding the upper atmospheres constantly interacting with nitrogen in the atmosphere to create an unstable form. of carbon, carbon-14.

What is the common feature of rubidium, potassium and carbon？

A．They can be made into clocks.

B．They are rich in content.

C．Their decay is slow but regular.

D．The products of their decay are the same.

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第7题

Milankovitch proposed in the early twentieth centurythat the ice ages were caused by varia

Milankovitch proposed in the early twentieth century

that the ice ages were caused by variations in the Earth’s

orbit around the Sun. For sometime this theory was

considered untestable, largely because there was no suffi-

(5) ciently precise chronology of the ice ages with which

the orbital variations could be matched.

To establish such a chronology it is necessary to

determine the relative amounts of land ice that existed

at various times in the Earth’s past. A recent discovery

(10) makes such a determination possible: relative land-ice

volume for a given period can be deduced from the ratio

of two oxygen isotopes, 16 and 18, found in ocean sedi-

ments. Almost all the oxygen in water is oxygen 16, but

a few molecules out of every thousand incorporate the

(15) heavier isotope 18. When an ice age begins, the conti-

nental ice sheets grow, steadily reducing the amount of

water evaporated from the ocean that will eventually

return to it. Because heavier isotopes tend to be left

behid when water evaporates from the ocean surfaces,

(20) the remaining ocean water becomes progressively

enriched in oxygen 18. The degree of enrichment can

be determined by analyzing ocean sediments of the

period, because these sediments are composed of calcium

carbonate shells of marine organisms, shells that were

(25) constructed with oxygen atoms drawn from the sur-

rounding ocean. The higher the ratio of oxygen 18 to

oxygen 16 in a sedimentary specimen, the more land ice

there was when the sediment was laid down.

As an indicator of shifts in the Earth’s climate, the

(30) isotope record has two advantages. First, it is a global

record: there is remarkably little variation in isotope

ratios in sedimentary specimens taken from different

continental locations. Second, it is a more continuous

record than that taken from rocks on land. Because of

(35) these advantages, sedimentary evidence can be dated

with sufficient accuracy by radiometric methods to

establish a precise chronology of the ice ages. The dated

isotope record shows that the fluctuations in global

ice volume over the past several hundred thousand years

(40) have a pattern: an ice age occurs roughly once every

100,000 years. These data have established a strong

connection between variations in the Earth’s orbit and

the periodicity of the ice ages.

However, it is important to note that other factors,

(45) such as volcanic particulates or variations in the amount

of sunlight received by the Earth, could potentially have

affected the climate. The advantage of the Milankovitch

theory is that it is testable: changes in the Earth’s orbit

can be calculated and dated by applying Newton’s laws

(50) of gravity to progressively earlier configurations of the

bodies in the solar system. Yet the lack of information

about other possible factors affecting global climate does

not make them unimportant.

In the passage, the author is primarily interested in______

A．suggesting an alternative to an outdated research method

B．introducing a new research method that calls an accepted theory into question

C．emphasizing the instability of data gathered from the application of a new scientific method

D．presenting a theory and describing a new method to test that theory

E．initiating a debate about a widely accepted theory

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第8题

The atmosphere that originally surrounded Earth was probably much different from the air w

The atmosphere that originally surrounded Earth was probably much different from

the air we breathe today. Earth's first atmosphere (some 4.6 billion years ago) was most

likely hydrogen and helium--the two most abundant gasses found in the universe--as

well as hydrogen compounds, such as methane and ammonia, Most scientists feel that

5 this early atmosphere escaped into space from the Earth's hot surface.

A second, more dense atmosphere, however, gradually enveloped Earth as gasses

from molten rocks within its hot interior escaped through volcanoes and steam vents.

We assume that volcanoes spewed out the same gasses then as they do today: mostly

water vapor (about 80 percent), carbon dioxide (about ten percent), and up to a few

10 percent nitrogen. These same gasses probably created Earth's second atmosphere.

As millions of years passed, the constant outpouring of gasses from the hot

interior--known as outgassing--provided a rich supply of water vapor, which formed

into clouds. Rain fell upon Earth for many thousands or years, forming the rivers,

lakes, and oceans of the world. During this Lime, large amounts of carbon dioxide were

15 dissolved in the oceans. Through chemical and biological processes, much of the carbon

dioxide became locked up in carbon sedimentary rocks, such as limestone. With much

of the water vapor already condensed into water and the concentration of carbon dioxide

dwindling, the atmosphere gradually became rich nitrogen.

It appears that oxygen, the second most abundant gas in today's atmosphere, probably

20 began an extremely slow increase in concentration as energetic rays from the sun split

water vapor into hydrogen and oxygen during a process called photodissociation. The

hydrogen, being lighter, probably rose and escaped into space, while the oxygen remained

in the atmosphere.

This slow increase in oxygen may have provided enough of this gas for primitive

25 plants to evolve, perhaps two to three billion years ago. Or the plants may have evolved

in an almost oxygen-free (anaerobic) environment. At any rate, plant growth greatly

enriched our atmosphere with oxygen. The reason for this enrichment is that plants, in

the presence of sunlight, process carbon dioxide and water to produce oxygen.

What is the main idea of the passage？

A．The original atmosphere on Earth was unstable.

B．The atmosphere on Earth has changed over time.

C．Hot underground gasses created clouds, which formed the Earth's atmosphere.

D．Plant growth depended on oxygen in the Earth's atmosphere.

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第9题

沉积相（sedimentary facies）

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第10题

According to a recent theory, Archean-age gold-quartzvein systems were formed over two bil

According to a recent theory, Archean-age gold-quartz

vein systems were formed over two billion years ago from

magmatic fluids that originated from molten granitelike

bodies deep beneath the surface of the Earth. This theory is

(5) contrary to the widely held view that the systems were

deposited from metamorphic fluids, that is, from fluids that

formed during the dehydration of wet sedimentary rocks.

he recently developed theory has considerable practical

importance. Most of the gold deposits discovered during

(10)the original gold rushes were exposed at the Earth’s surface

and were found because they had shed trails of alluvial

gold that were easily traced by simple prospecting methods.

Although these same methods still lead to an occasional

discovery, most deposits not yet discovered have gone

(15) undetected because they are buried and have no surface

expression.

The challenge in exploration is therefore to unravel the

subsurface geology of an area and pinpoint the position of

buried minerals. Methods widely used today include

(20) analysis of aerial images that yield a broad geological

overview; geophysical techniques that provide data on the

magnetic, electrical, and mineralogical properties of the

rocks being investigated; and sensitive chemical tests that

are able to detect the subtle chemical halos that often

(25) envelop mineralization. However, none of these high-

technology methods are of any value if the sites to which

they are applied have never mineralized, and to maximize

the chances of discovery the explorer must therefore pay

particular attention to selecting the ground formations most

(30) likely to be mineralized. Such ground selection relies to

varying degrees on conceptual models, which take into

account theoretical studies of relevant factors.

These models are constructed primarily from empirical

observations of known mineral deposits and from theories

35) of ore-forming processes. The explorer uses the models to

identify those geological features that are critical to the

formation of the mineralization being modeled, and then

tries to select areas for exploration that exhibit as many of

the critical features as possible.

The author is primarily concerned with______

A．advocating a return to an older methodology

B．explaining the importance of a recent theory

C．enumerating differences between two widely used methods

D．describing events leading to a discovery

E．challenging the assumptions on which a theory is based

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