2010.8 阅读背景资料/原文详细版

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2.1.4. 海豚声音的背景资料：
Every dolphin has its own unique 'signature whistle'. Listening to these whistles is one way to identify specific dolphins and track their whereabouts.
Echolocation - the location of objects by their echoes - is a highly specialized faculty that enables dolphins to explore their environment and search out their prey in a watery world where sight is often of little use. As sound travels four and a half times faster in water than in air, the dolphin's brain must be extremely well adapted in order to make a rapid analysis of the complicated information provided by the echoes.
Although the ability to echolocate has only been proven experimentally for a few odontocete species, the anatomical evidence - the presence of the melon, nasal sacs and specialized skull structures - suggests that all dolphins have this ability.
The dolphin is able to generate sound in the form of clicks, within its nasal sacs, situated behind the melon. The frequency of this click is higher than that of the sounds used for communication and differs between species. The melon acts as a lens which focuses the sound into a narrow beam that is projected in front of the animal.
When the sound strikes an object, some of the energy of the soundwave is reflected back towards the dolphin. It would appear that the panbone in the dolphin's lower jaw receives the echo, and the fatty tissue behind it transmits the sound to the middle ear and thence to the brain. It has recently been suggested that the teeth of the dolphin, and the mandibular nerve that runs through the jawbone may transmit additional information to the dolphin's brain.
As soon as an echo is received, the dolphin generates another click. The time lapse between click and echo enables the dolphin to evaluate the distance between it and the object; the varying strength of the signal as it is received on the two sides of the dolphin's head enable it to evaluate direction. By continuously emitting clicks and receiving echoes in this way, the dolphin can track objects and home in on them.
The echolocation system of the dolphin is extremely sensitive and complex. Using only its acoustic senses, a bottlenose dolphin can discriminate between practically identical objects which differ by ten per cent or less in volume or surface area. It can do this in a noisy environment, can whistle and echolocate at the same time, and echolocate on near and distant targets simultaneously - feats which leave human sonar experts gasping.

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2.2.2. 地球降温
节选自Plateau Uplift and Climate Change (Scientific American Magazine @ March 1991)
Author：William F. Ruddiman and John E. Kutzbach

During the past 40 million years, and particularly during the past 15 million years, this warm, wet climate largely disappeared. Colder climates and much greater regional extremes of precipitation have developed. What caused this cooling and diversification of climate and vegetation into a complex mosaic of many regionally distinctive types?

One school of thought focuses on the changing positions of the earth’s continents and oceans. The Atlantic Ocean has expanded at the expense of the Pacific Ocean, whereas an ancient equatorial sea that extended across much of Eurasia (called the Tethys Sea) has shrunk to become the modern, much smaller Mediterranean Sea. In addition, the fraction of continents flooded by shallow inland seas has slowly decreased, exposing large amounts of land and creating climates less moderated by the temperature-stabilizing effects of oceans. Computer model simulations show that changes in the arrangement of the continents and the size of inland seas can have important effects on global climate over very long intervals of geologic time. But they are significantly less convincing as sole explanations for the dramatic changes of the past 40 million years.

Another possibility is a long-term decline in the concentration of carbon dioxide in the atmosphere, which would lessen the amount of heat trapped by the atmosphere and lead to “greenhouse cooling.” The amount of carbon dioxide in the earth’s atmosphere over million-year timescales is controlled by two major processes. Chemical weathering of continental rocks removes carbon dioxide from the atmosphere and carries it in dissolved chemical from to the ocean, where it is taken in by marine biota and deposited in sediments on the seafloor. Tectonic activity eventually frees this trapped carbon dioxide, in the earth’s lithospheric plates transports the seafloor to ocean trenches, where subduction carries old crust and sediments down toward the earth’s hot interior. At great depths, the sediments melt, releasing carbon dioxide, which emerges from the volcanic islands that overlie the buried curst and rejoins the atmosphere, completing the cycle.

If the pace of seafloor spreading (and hence of subduction) slowed significantly, less carbon dioxide would be vented to the atmosphere, the atmosphere would become relatively depleted of carbon dioxide and temperatures would fall. In fact, globally averaged seafloor spreading rates slow little or no net change in the past 40 million years. Subduction and volcanism eventually return the carbon dioxide to the atmosphere, but this process requires a long time (tens to hundreds of millions of years) to complete.

Plateau uplift may alter climate by increasing chemical weathering of rocks, thereby reducing atmospheric carbon dioxide concentrations. Carbon dioxide combines with rainwater and ground water to form carbonic acid, which reacts with silicate minerals in rocks during weathering. The resulting bicarbonate ions drain into the oceans, where they are taken up by marine animals such as plankton and corals and eventually deposited on the seafloor. The net effect is that chemical weathering removes carbon dioxide from the atmosphere and locks it away at the bottom of the oceans.

Maureen Raymo proposed that uplift of plateaus and mountain ranges has increased the rate of chemical erosion of continental rock on the globally averaged basis. Uplift could enhance chemical weathering in several ways. Heavy monsoons, which develop at the margins of plateaus, unleash particularly intense rainfall. In these regions, uplift-related faulting and folding also expose fresh rock to the weathering process. Moreover, the steeper slopes created by plateau uplift cause faster runoff, which removes erosion products and intensifies the chemical attack on the rock. Raymo suggests that long-term uplift in Tibet and other regions may have increased the rate at which carbon dioxide is removed from the atmosphere. In this way, concentrations would have fallen even though the amount of carbon dioxide exhaled by volcanoes (as inferred from seafloor spreading rates) remained nearly constant. Falling carbon dioxide levels would reduce the ability of the atmosphere to retain heat, thereby amplifying the global cooling.

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2.1.6. 鸟类声音系统的进化
原文后两段
A few years ago, Jarvis and his colleagues made the surprising discovery that when a songbird, parrot or hummingbird is producing its learned vocalization, a set of seven similar structures in the birds’ brains become active. The finding was unexpected because the three avian groups are only distantly related to one another. At the same time, they are closely related to other birds that are not vocal learners. Flycatchers, for example, belong to the same order as songbirds—Passeriformes—yet no flycatcher species tested so far displays the trait. One possible explanation, says Jarvis, is that the three groups of vocal learning birds had a common ancestor that possessed the skill. “But this means there would have been multiple losses of the ability over time, a sort of mass extinction of vocal learning,” he says. Another hypothesis is that vocal learners evolved similar brain structures independently over the last 65 million years, much the same way that birds and bats separately evolved wings that turned out to be so much alike.

Discoveries about the human brain support this latter hypothesis. Scientists conducting imaging studies have found that when people speak, parts of their brains’ cerebrums that are similar to those of vocalizing songbirds, parrots and hummingbirds become active. They’ve also found that the same neural pathways are damaged in people who have lost the ability to speak due to injury or stroke. Jarvis now believes that vocal learning most likely developed independently in humans and the three bird groups (as well as in other learners whose brains have not been studied)—yet it arose from a pre-existing brain system, probably shared by all vertebrates, that controls learning to move.

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1.1.12. 捆绑销售策略
Reference: dec0412. 打了好一会字, 然后未保存丢失… 再打一遍……
Definition of "Bundling": Sometimes companies bundle products together in order to promote a new product or to encourage consumers to try a complementary product, such as a free small conditional bundled with a shampoo purchase, or a free disposable razor with a shaving cream purchase. A company may also offer a bonus pack or a special pack with 20% more in order to encourage a customer to purchase a product.
边打这个边想起COX：昨天晚上COX送了一个大箱子过来，结果只有一根网线和大半箱广告。

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1.1.10. 工作紧密性与跳槽
近似原文(原文也许为此稿缩略版) vitalia
According to Mitchell et al. (2001), job embeddedness represents a broad cluster of ideas that influence an employee's choice to remain in a job, operating like a net or a web in which an individual becomes enmeshed. A person who is highly embedded has many connections within a perceptual life space (Lewin, 1951). Moreover, a person can become enmeshed or embedded in a variety of ways (both on and off the job). The critical aspects of job embeddedness are the extent to which the job is similar to or fits with the other aspects in their life space, the extent to which the person has links to other people or activities, and the ease with which links can be broken--what they would give up if they left. These dimensions are called fit, links and sacrifice. Less concerned with the influence of any one specific connection, job embeddedness focuses on the overall level of connectedness (Mitchell et al., 2001).
（介绍工作嵌入度的三个方面：fit （适合）, links（联系） and sacrifice（损失）

According to the theory of job embeddedness (Mitchell, Holtom and Lee, 2001), an employee's personal values, career goals and plans for the future must fit with the larger corporate culture and the demands of his or her immediate job (e.g., job knowledge, skills and abilities). In addition, a person will consider how well he or she fits the community and surrounding environment. Job embeddedness assumes that the better the fit, the higher the likelihood that an employee will feel professionally and personally tied to the organization.
（讲第一方面----fit（适合），员工的个人价值，职业目标和未来计划必须与公司文化以及他/她个人的工作相一致，也就是fit。员工自己也会考虑自己是否fit其所属团体与环境。越fit，员工越有归属感，越不会跳槽。）

Job embeddedness theory suggests that a number of threads link an employee and his or her family in a social, psychological, and financial web that includes work and non-work friends, groups, the community, and the physical environment where they are located. The greater the number of links between the person and the web, the more likely an employee will stay in a job (Mitchell et al., 2001).
（讲第二方面----Link（联系）。与方方面面联系越紧密，员工越愿意留在公司。）（注意这段的小列举）

The concept of sacrifice represents the perceived cost of material or psychological benefits that are forfeited by organizational departure. For example, leaving an organization may induce personal losses (e.g., losing contact with friends, personally relevant projects, or perks). The more an employee will have to give up when leaving, the more difficult it will be to sever employment with the organization (Shaw et al., 1998). Examples include non-portable benefits, like stock options or defined benefit pensions, as well as potential sacrifices incurred through leaving an organization like job stability and opportunities for advancement (Shaw et al., 1998). Similarly, leaving a community where they are highly involved in local organizations can be difficult for employees.
（讲第三方面----sacrifice（损失）。员工在各方面损失越大，越不愿跳槽）（注意这段的小列举）

One key area where job embeddedness complements traditional approaches to voluntary turnover is community attachment. The model explicitly considers the impact of both organizational and community influences on the three job embeddedness dimensions. Put differently, each of the three dimensions--fit, links and sacrifice--has organizational and community components, which are summarized in Table 2. In two reported tests, Mitchell, Lee and colleagues (Mitchell et al., 2001; Lee et al., 2004) have demonstrated that job embeddedness predicts variance in voluntary turnover over and above job satisfaction.
（讲job embeddedness（工作嵌入度）对理解主动跳槽有一个重要的补充，这就是归属感。Job embeddness模型认为组织（偏公）和社团（偏私）对job embeddedness的三个方面------fit, links and sacrifice都有影响。模型作者认为：在预测员工“主动跳槽”方面，job embeddedness比job satisfaction更有优势。）

To date, job embeddedness has been tested in the hospital, grocery and banking industries. To extend the generalizability of the model, we propose to test it across multiple, diverse industries. Thus, the following hypotheses replicate Mitchell et al.'s findings:

Hypothesis 1: Job embeddedness is negatively correlated with voluntary turnover （主动跳槽）.
（工作嵌入度越高，员工越不愿跳槽. Job embeddedness 和 turnover是 反比关系）
Hypothesis 2: Job embeddedness improves the prediction of voluntary turnover above and beyond that accounted for by job satisfaction（工作满意度）.
（job embeddedness工作嵌入度的大小，对员工跳槽的影响要超过job satisfaction工作满意度大小对员工跳槽的影响。）

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2.1.4. 《研究地质时间》
Scientific American @ Jan 1990
The Yugoslav astronomer Milutin Milankovitch refined and formalized the hypothesis in the 1920’s and 1930’s.The astronomical pacemaker he advocated has three components, two that change the intensity of the seasons and a third that affects the interaction between the two driving factors. The first is the tilt of the earth’s spin axis. Currently about 23.5 degrees from the vertical, it fluctuates from 21.5 degrees to 24.5 degrees and back every 41,000 years. The greater the tilt is, the more intense seasons in both hemispheres become: summers get hotter and winter colder.

The second, weaker factor controlling seasonality is the shape of the earth’s orbit. Over a period of 100,000 years, the orbit stretches into a more eccentric ellipse and then grows more nearly circular again. As the orbital eccentricity increases, the difference in the earth’s distance from the sun at the orbit’s nearest and farthest points grows, intensifying the seasons in one hemisphere and moderating them in the other. (At present the earth reaches its farthest point during the Southern Hemisphere winter; as a result, southern winters are a little colder – than their northern counterparts.)

A third astronomical fluctuation governs the interplay between the tilt and eccentricity effects. It is the precession, or wobble, of the earth’s spin axis, which traces out a complete circle on the background of stars about every 23,000 years. The precession determines whether summer in a given hemisphere falls at near or a far point in the orbit– in other words, whether tilt seasonality is enhanced or weakened by distance sesonablity. When these two controllers of seasonality reinforce each other in one hemisphere, they oppose each other in the opposite hemisphere.

Milankovitch calculated that these three factors work together to vary the amount of sunshine reaching the high northern latitudes in summer over a range of some 20 percent – enough, he argued, to allow the great ice sheets that advanced across the northern continents to grow during intervals of cool summers and mild winters. For many years, however, the lack of an independent record of ice-age timing made the hypothesis untestable.

In the early 1950’s Cesare Emiliani produced the first complete record of the waxings and waning of past glaciations. It came from a seemingly odd place, the sea floor. Single-cell marine organisms called foraminifera house themselves in shells made of calcium carbonate. When the foraminifera die, sink to the bottom and contribute to these a-floor sediments, the carbonate of their shells preserves certain characteristics of the seawater they inhabited. In particular, the ratio of a heavy isotope of oxygen (oxygen 18) to ordinary oxygen (oxygen 16) in the carbonate preserves the ratio of the two oxygen atoms in the water molecules.

It is now understood that the ratio of oxygen isotopes in seawater closely tracks the proportion of the world’s water that is locked up in glaciers and ice sheets. A kind of meteorological distillation accounts for the link. Water molecules containing the heavier isotope tend to condense and fall as precipitation a tiny bit more readily than molecules containing the lighter isotope. Hence, as water evaporated from warm oceans moves away from the source, its oxygen 18 preferentially returns to the oceans in precipitation. What ultimately falls as snow on ice sheets and mountain glaciers is relatively depleted of oxygen 18. As the oxygen 18-poorice builds up, the oceans become relatively enriched in the isotope. The larger the ice sheets grow, the higher the proportion of oxygen 18 becomes in seawater – and hence in the sediments.

Analyzing cores drilled from seafloor sediments, Emiliani found that the isotopic ratio rose and fell in rough accord with the cycles Milankovitch had predicted. A chronology for the combined record showed in 1976 that the record contains the very same periodicities as the orbital process.

……

Others have found that during the last ice age the earth’s mountain glaciers also expanded. The evidence – from the heaps of debris plowed up by the glaciers, knows as moraines – is as clear in the tropics and the southern temperate latitudes. On all the mountains studied so far, regardless of geographic setting or precipitation rate, the snow line descended by about one kilometer, corresponding to a drop in temperature of about five degrees Celsius.

Where organic material was trapped in the moraines, radio carbon dating shows that the glaciers advanced and retreated on the same schedule. They fluctuated near their maximum extent between about 19,500 and 14,000 years ago, about the same time as the glaciations of northern ice sheets began to shrink, the mountain glaciers underwent a dramatic retreat that sharply reduced their size by about 12,500 years ago.

How could changes in summer sunshine at the latitude of Iceland have caused glaciers to grow and retreat in New Zealand and the southern Andes? If orbital cycles do indeed drive glacial cycles by acting directly on northern ice sheets, the response to seasonality changes in the high northern latitudes must be strong enough to override the effects of the very different changes in the Southern Hemisphere. One possibility is that the northern ice sheets themselves translate Northern Hemisphere seasonality into climatic change around the world.

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2.2.1. 《火山熔岩》
The Origin of the Land under the Sea (Scientific American Magazine @ February 2009)
Author: Peter B. Kelemen

Knowledge of the intense heat and pressure in the mantle led researchers to hypothesize in the late 1960s that ocean crust originates as tiny amounts of liquid rock known as melt—almost as though the solid rocks were “sweating.” Even a minuscule release of pressure (because of material rising from its original position) causes melt to form in microscopic pores deep within the mantle rock. Explaining how the rock sweat gets to the surface was more difficult. Melt is less dense than the mantle rocks in which it forms, so it will constantly try to migrate upward, toward regions of lower pressure. But what laboratory experiments revealed about the chemical composition of melt did not seem to match up with the composition of rock samples collected from the mid-ocean ridges, where eruptedmelt hardens. Using specialized equipment to heat and squeeze crystals from mantle rocks in the laboratory, investigators learned that the chemical composition of melt in the mantle varies depending on the depth at which it forms; the composition is controlled by an exchange of atoms between the melt and the minerals that makeup the solid rock it passes through. The experiments revealed that as melt rises, it dissolves one kind of mineral, orthopyroxene, and precipitates, or leaves behind, another mineral, olivine. Researchers could thus infer that the higher in the mantle melt formed, the moreorthopyroxene it would dissolve, and the more olivine it would leave behind.(melt上升时， 溶解Ort产生Oli, 所以melthigher， 溶解的Ort越多，产生的/留在身后的Oli也越多) Comparing these experimental findings with lava samples from the mid-ocean ridges revealed that almost all of them have the composition of melts that formed at depths greater than 45kilometers. This conclusion spurred a lively debate about how meltis able to rise through tens of kilometers of overlying rock while preserving the composition appropriate for a greater depth. If melt rose slowly in smallpores in the rock, as researchers suspected, it would be logical to assume that all melts would reflect the composition of the fashallowest part of the mantle,at 10 kilometers or less. Yet the composition of most mid-ocean ridge lavas amples suggests their source melt migrated through the uppermost 45 kilometers of the mantle without dissolving any orthopyroxene from the surrounding rock. But how? （疑大概为狗狗第一段的背景内容）

In the early 1970s scientists proposed an answer: the melt must make the last leg of its upward journey along enormous cracks. Open cracks would allow the melt to rise so rapidly that it would not have time to interact with the surrounding rock, nor would melt in the core of the crack ever touch the sides. Although open cracks are not a natural feature of the upper mantle— the pressure is simply too great—some investigators suggested that the buoyant force of migrating melt might sometimes be enough to fracture the solid rock above, like an icebreaker ship forcing its way through polar pack ice. Adolphe Nicolas of the University of Montpellier in France and his colleagues discovered tantalizing evidence for such cracks while examining unusual rock formations called ophiolites. Typically, when oceanic crust gets old and cold, it becomes so dense that it sinks back into the mantle along deep trenches known as subduction zones, such as those that encircle the Pacific Ocean. Ophiolites, on the other hand, are thick sections of old seafloor and adjacent, underlying mantle that are thrust up onto continents when two of the planet’s tectonic plates collide. A famous example, located in the Sultanate of Oman, was exposed during the ongoing collision of the Arabian and Eurasian plates. In this and other ophiolites, Nicolas’s team found unusual, light-colored veins called dikes, which they interpreted as cracks in which melt had crystallized before reaching the seafloor. The problem with this interpretation was that the dikes are filled with rock that crystallized from a melt that formed in the uppermost reaches of the mantle, not below 45 kilometers, where most mid-ocean ridge lavas originate. In addition, the icebreaker scenario may not work well for the melting region under mid-ocean ridges: below about 10 kilometers, the hot mantle tends to flow like caramel left too long in the sun, rather than cracking easily.

To explain the ongoing mystery, I began working on an alternative hypothesis for lava transport in the melting region. In my dissertation in the late 1980s, I developed a chemical theory proposing that as rising melt dissolves orthopyroxene crystals, it precipitates a smaller amount of olivine, so that the net result is a greater volume of melt. Our calculations revealed how this dissolution process gradually enlarges the open spaces at the edges of solid crystals, creating larger pores and carving a more favorable pathway through which melt can flow. As the pores grow, they connect to form elongate channels. In turn, similar feedbacks drive the coalescence of several small tributaries to form larger channels. Indeed, our numerical models suggested that more than90 percent of the melt is concentrated into less than 10 percent of the available area. That means millions of microscopic threads of flowing melt may eventually feed into only a few dozen, high porosity channels 100 meters or more wide. Even in the widest channels, many crystals of the original mantle rock remain intact, congesting the channels and inhibiting movement of the fluid. That is why melt flows slowly, at only a few centimeters a year. Over time, however, so much melt passes through the channels that all the soluble orthopyroxene crystals dissolve away, leaving only crystals of olivine and other minerals that the melt is unable to dissolve. As a result, the composition of the melt within such channels can no longer adjust to decreasing pressure and instead records the depth at which it last “saw” an orthopyroxene crystal. One of the most important implications of this process, called focused porous flow, is that only the melt at the edges of channels dissolves orthopyroxene from the surrounding rock; melt within the inner part of the conduit can rise unadulterated.

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2.1.5. 《八哥学说话》英语原版出处：
Social influences on vocal development
Author: Charles T. Snowdon, Martine Hausberger

The vocal talent of starlings has been known since antiquity, when Pliny considered their ability to mimic human speech noteworthy. Ornithologists know that this species possesses a rich repertoire of call and songs, composed of whistles, clicks, snarls, and screeches. In addition, starlings are well known for their ability to mimic the sounds of other animals or even mechanical noises. Descriptions of starling song in the past reflect the difficulty of describing all the variety of sounds included. Witherby mentioned a “lively rambling melody of throaty warbling, chiring, clicking and gurgling notes interspersed with musical whistles and pervaded by a peculiar creaking quality.”
This complexity explains why detailed studies of starling song have delayed long after the arrival of the sound spectrograph. As mentioned by West & King, “the problem with starlings is that they vocalized too much, too often and in too great numbers, sometimes in choruses numbering in the thousands. Even the seemingly elementary step of creating an accurate catalogue of the vocal repertoire of wild starlings is an intimidating task because of the variety of their sounds.”

Chaiken have compared the sons of young males raised in different social conditions: either with a wild-caught adult song tutor, individually housed but tape-tutored by a tape-recording or raised in total isolation. All birds had been taken from the nest at an early age (8-10 days) and were hand raised. Untutored birds produced mostly an abnormal song, where even the basic organization of song was missing. In contrast, both tape- and live-tutored birds developed songs with a normal basic organization, but with some syntactical abnormalities for the tape-tutored birds. Tape-tutored birds had repertoires half as large as those of live-tutored birds. Large differences occurred between both groups of birds in their …

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2.3.1 《金星氢元素逃逸》 英语原版出处：
Global Climate Change on Venus (New Light on the Solar System; Special Editions)
Author: Mark A. Bullock and David H. Grinspoon

THE STUNNING DIFFERENCES between the climates of Earth and Venus today are intimately linked to the history of water on these two worlds. Liquid water is the intermediary in reactions of carbon dioxide and surface rocks that can form minerals. In addition, water mixed into the underlying mantle is probably responsible for the low-viscosity layer, orasthenosphere, on which Earth’s lithospheric plates slide. The formation of carbonate minerals and their subsequent descent on tectonic plates prevent carbon dioxide from building up. Models of planet formation predict that the two worlds should have been endowed with roughly equal amounts of water, delivered by the impact of icy bodies from the outer solar system. But, when the Pioneer Venus mission went into orbit in 1978, it measured the ratio of deuterium to ordinary hydrogen within the water of Venus’s clouds. The ratio was an astonishing 150times the terrestrial value. The most likely explanation is that Venus once had far more water and lost it. When water vapor drifted into the upper atmosphere, solar ultraviolet radiation decomposed it into oxygen and either hydrogen or deuterium. Because hydrogen, being lighter, escapes to space more easily, the relative amount of deuterium increased. Why did this process occur on Venus but not on Earth? In 1969 Andrew P. Ingersoll of the California Institute of Technology showed that if the solar energy available to a planet were strong enough, any water at the surface would rapidly evaporate. The added water vapor would further heat the atmosphere and set up what he called the runaway greenhouse effect. The process would transport the bulk of the planet’s water into the upper atmosphere, where it would ultimately be decomposed and lost. Later James F. Kasting of Pennsylvania State University and his co-workers developed a more detailed model of this effect. They estimated that the critical solar flux required to initiate a runaway greenhouse was about 40 percent larger than the present flux on Earth. This value corresponds roughly to the solar flux expected at the orbit of Venus shortly after it was formed, when the sun was 30 percent fainter. An Earth ocean’s worth of water could have fled Venus in the first 30 million years of its existence. A shortcoming of this model is that if Venus had a thick carbon dioxide atmosphere early on, as it does now, it would have retained much of its water. The amount of water that is lost depends on how much of it can rise high enough to be decomposed—which is less for a planet with a thick atmosphere. Furthermore, any clouds that developed during the process would have reflected sunlight back into space and shut off the runaway greenhouse. So Kasting’s group also considered a solar flux slightly below the critical value. In this scenario, Venus had hot oceans and a humidstratosphere. The seas kept levels of carbon dioxide low by dissolving the gas and promoting carbonate formation. With lubrication from water in theasthenosphere, plate tectonics might have operated. In short, Venus possessed climate-stabilizing mechanisms similar to those on Earth today. But the atmosphere’s lower density could not prevent water from diffusing to high altitudes. Over 600 million years, an ocean’s worth of water vanished. Any plate tectonics shut down, leaving volcanism and heat conduction as the interior’s ways to cool. Thereafter carbon dioxide accumulated in the air.

This picture, termed the moist greenhouse, illustrates the intricate interaction of solar, climate and geologic change. Atmospheric and surface processes can preserve the status quo, or they can conspire in their own destruction. If the theory is right, Venus once had oceans—perhaps even life, although it may be impossible to know.

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2.1.1. 《微眼动》的英语原版出处：
Windows on the Mind (Scientific American Magazine @ August 2007)

And yet only recently have researchers come to appreciate the profound importance of such “fixational” eye movements. For five decades, a debate has raged about whether the largest of these involuntary movements, the so-called microsaccades, serve any purpose at all. Some scientists have opined that microsaccades might even impair eyesight by blurring it. But recent work has made the strongest case yet that the seminuscule ocular meanderings separate vision from blindness when a person looks out at a stationary world.

Indeed, animal nervous systems have evolved to detect changes in the environment, because spotting differences promotes survival. Motion in the visual field may indicate that a predator is approaching or that prey is escaping. Such changes prompt visual neurons to respond with electrochemical impulses. Unchanging objects do not generally pose a threat, so animal brains – and visual systems – did not evolve to notice them. Frogs are an extreme case. A fly sitting still on the wall is invisible to a frog, as are all static objects. But once the fly is aloft, the frog will immediately detect it and capture it with its tongue.

Frogs cannot see unmoving objects because, as Helmholtz hypothesized, an unchanging stimulus leads to neural adaptation, in which visual neurons adjust their output such that they gradually stop responding. Neural adaptation saves energy but also limits sensory perception. Human visual system does much better than a frog’s at detecting unmoving objects, because human eyes create their own motion. Fixational eye movements shift the entire visual scene across the retina, prodding visual neurons into action and counteracting neural adaptation. They thus prevent stationary objects from fading away.

The results of these experiments, published in 2000 and 2002, showed that microsaccades increased the rate of neural impulses generated by both LGN and visual cortex neurons by ushering stationary stimuli, such as the bar of light, in and out of a neuron’s receptive field, the region of visual space that activates it. This finding bolstered the case that microsaccades have an important role in preventing visual fading and maintaining a visible image. And assuming such a role for microsaccades, our neuronal studies of microsaccades also began to crack the visual system’s code for visibility. In our monkey studies we found that microsaccades were more closely associated with rapid bursts of spikes than single spikes from brain neurons, suggesting that bursts of spikes are a signal in the brain that something is visible.

In our experiments, we asked volunteers to perform a version of Troxler’s fading task. Our subjects were to fixate on a small spot while pressing or releasing a button to indicate whether they could see a static peripheral target. The target would vanish and then reappear as each subject naturally fixated more – and then less – at specific times during the course of the experiment. During the task, we measured each person’s fixational eye movements with a high-precision video system.

As we had predicted, the subjects’ microsaccades became sparser, smaller and slower just before the target vanished, indicating that a lack of microsaccades– leads to adaptation and fading. Also consistent with our hypothesis, microsaccades became more numerous, larger and faster right before the peripheral target reappeared. These results, published in 2006, demonstrated for the first time that microsaccades engender visibility when subjects try to fix their gaze on an image and that bigger and faster microsaccades work best for this purpose. And because the eyes are fixating – resting between the larger, voluntary saccades – in the vast majority of the time, microsaccades are critical for most visual perception.