分享和跟踪记录自己连阅读的材料

Rabbit_Carrot

准备根据机经搜索一些类似的文章
还有包括官方资料类似的。

Rabbit_Carrot

About 252 million years ago, more than 96 percent of ocean life and 70 percent of land-based life forms died in an event known as the end-Permian extinction. The mass die-off happened in a geologic flash of just 60,000 years. Scientists have proposed everything from massive meteor impacts to coal explosions to rifting supercontinents to explain this cataclysmic extinction.Rocks from that time period in locations such as Meishan, China, show that atmospheric carbon-dioxidelevels skyrocketed right around the time of the extinction. Sediments also show that during this time, the largest set of volcanic eruptions in recorded geologic history — called the Siberian Traps — spewed enough lava to cover the entire landmass of the United States, said study co-author Gregory Fournier, a biologist at the Massachusetts Institute of Technology. Therefore, many researchers have theorized that the Siberian Traps could have belched out the extra carbon dioxide, choking life on the planet.

But if volcanic eruptions caused the great dying, shifts in carbon should occur as big bursts followed by gradual decays. Instead, the carbon-dioxide (CO2) levels rose at faster-than-exponential rates, which points to a biological cause of the shift, the researchers said.The team wondered whether methane-producing bacteria— in particular, a genus known as Methanosarcina — could have caused the carbon-dioxide overdose. In this theory, microbes that munched on the carbon-based chemical acetate produced huge amounts of methane, which would then be converted into CO2 by other microbes. The formation of CO2, in turn, would have used up free oxygen in the atmosphere. Those oxygen-starved conditions could have then caused a cascade of events that made life impossible.

The team used rates of gene mutation to estimate that Methanosarcina acquired the genes to make methane from acetate about 250 million years ago, right around the time of the extinction.But in order to produce so much methane so quickly, the microbes would have needed ample supplies of nickel for critical metabolic functions.Sure enough, when the team looked at the geological sediments, they found the volcanic activity at the time had produced transient surges in nickel. The volcanism also initially led to oxygen-starved conditions in the oceans, which prevented the normal microbial communities from breaking down carbon, leaving a huge stockpile of acetate.Enter Methanosarcina. With their newly evolved ability to break down acetate, they flourished, producing more methane. This methane production created a positive feedback loop, worsening the oxygen-starved conditions that allowed them to take over in the first place.

The findings suggest the Siberian Traps may have fueled the massive bloom in methane-producing microbes. That, in turn, caused carbon-dioxide levels to skyrocket, acidifying the oceans (because the dissolved CO2 turns into carbonic acid in the sea), warming the planet and poisoning the air.
"The volcano was the catalyst or the primer for the much larger release of CO2 that was caused biologically," Fournier told Live Science.But although the bacteria played a large role, there was probably a cascade of interdependent events that led to such a catastrophic decline."It could have been a very-long-term successive disruption of all of Earth's ecosystems," Fournier said.The amount of methane-producing bacteria subsided after about 100,000 years, but the damage had been done: It would take another 30 million years for the diversity of life to rebound, Fournier said.The findings are detailed today (March 31) in the journal Proceedings of the National Academy of Sciences.

Rabbit_Carrot

自然科学类

琥珀和树脂
http://www.yaksr.com/resin.html

细菌灭绝 觉得这篇非常GMAT
http://www.livescience.com/44491-microbes-caused-mass-extinction.html

Rabbit_Carrot

About 252 million years ago, more than 96 percent of ocean life and 70 percent of land-based life forms died in an event known as the end-Permian extinction. The mass die-off happened in a geologic flash of just 60,000 years. Scientists have proposed everything from massive meteor impacts to coal explosions to rifting supercontinents to explain this cataclysmic extinction.Rocks from that time period in locations such as Meishan, China, show that atmospheric carbon-dioxidelevels skyrocketed right around the time of the extinction. Sediments also show that during this time, the largest set of volcanic eruptions in recorded geologic history — called the Siberian Traps — spewed enough lava to cover the entire landmass of the United States, said study co-author Gregory Fournier, a biologist at the Massachusetts Institute of Technology. Therefore, many researchers have theorized that the Siberian Traps could have belched out the extra carbon dioxide, choking life on the planet.

But if volcanic eruptions caused the great dying, shifts in carbon should occur as big bursts followed by gradual decays. Instead, the carbon-dioxide (CO2) levels rose at faster-than-exponential rates, which points to a biological cause of the shift, the researchers said.The team wondered whether methane-producing bacteria— in particular, a genus known as Methanosarcina — could have caused the carbon-dioxide overdose. In this theory, microbes that munched on the carbon-based chemical acetate produced huge amounts of methane, which would then be converted into CO2 by other microbes. The formation of CO2, in turn, would have used up free oxygen in the atmosphere. Those oxygen-starved conditions could have then caused a cascade of events that made life impossible.The team used rates of gene mutation to estimate that Methanosarcina acquired the genes to make methane from acetate about 250 million years ago, right around the time of the extinction.But in order to produce so much methane so quickly, the microbes would have needed ample supplies of nickel for critical metabolic functions.Sure enough, when the team looked at the geological sediments, they found the volcanic activity at the time had produced transient surges in nickel. The volcanism also initially led to oxygen-starved conditions in the oceans, which prevented the normal microbial communities from breaking down carbon, leaving a huge stockpile of acetate.Enter Methanosarcina. With their newly evolved ability to break down acetate, they flourished, producing more methane. This methane production created a positive feedback loop, worsening the oxygen-starved conditions that allowed them to take over in the first place.

The findings suggest the Siberian Traps may have fueled the massive bloom in methane-producing microbes. That, in turn, caused carbon-dioxide levels to skyrocket, acidifying the oceans (because the dissolved CO2 turns into carbonic acid in the sea), warming the planet and poisoning the air.
"The volcano was the catalyst or the primer for the much larger release of CO2 that was caused biologically," Fournier told Live Science.But although the bacteria played a large role, there was probably a cascade of interdependent events that led to such a catastrophic decline."It could have been a very-long-term successive disruption of all of Earth's ecosystems," Fournier said.The amount of methane-producing bacteria subsided after about 100,000 years, but the damage had been done: It would take another 30 million years for the diversity of life to rebound, Fournier said.The findings are detailed today (March 31) in the journal Proceedings of the National Academy of Sciences.

Rabbit_Carrot

Don't adjust your color settings—the Grand Prismatic Spring really is rainbow colored, following the spectrum of white light through a prism (red to blue). The spring was first officially described, and named, by the Hayden Expedition in 1871, which was the first federally-funded exploration of what became Yellowstone. But what causes the hot spring's magnificent coloration? It's all thanks to the heat-loving bacteria that call the
Read more http://www.smithsonianmag.com/travel/science-behind-yellowstones-rainbow-hot-spring-180950483/

Rabbit_Carrot

The evolution of intelligence among early large mammals of the grasslands was due in great measure to the interaction between two ecologically synchronized groups of these animals, the hunting carnivores and the herbivores that they hunted. The interaction resulting from the differences between predator and prey led to a general improvement in brain functions; however, certain components of intelligence were improved far more than others.

The kind of intelligence favored by the interplay of increasingly smarter catchers and increasingly keener escapers is defined by attention — that aspect of mind carrying consciousness forward from one moment to the next. It ranges from a passive, free floating awareness to a highly focused, active fixation. The range through these states is mediated by the arousal system, a network of tracts converging from sensory systems to integrating centers in the brain stem. From the more relaxed to the more vigorous levels, sensitivity to novelty is increased. The organism is more awake, more vigilant; this increased vigilance results in the apprehension of ever more subtle signals as the 15 organism becomes more sensitive to its surroundings. The processes of arousal and concentration give attention its direction. Arousal is at first general, with a flooding of impulses in the brain stem; then gradually the activation is channeled. Thus begins concentration, the holding of consistent images. One meaning of intelligence is the way in which these images and other alertly searched information are used in the context of previous experience. Consciousness links past attention to the present and permits the integration of details with perceived ends and purposes.

The elements of intelligence and consciousness come together marvelously to produce different styles in predator and prey. Herbivores and carnivores develop different kinds of attention related to escaping or chasing. Although in both kinds of animal, arousal stimulates the production of adrenaline and norepinephrine by the adrenal glands, the effect in herbivores is primarily fear, whereas in carnivores the effect is primarily aggression. For both, arousal attunes the animal to what is ahead. Perhaps it does not experience forethought as we know it, but the animal does experience something like it. The predator is searchingly aggressive, inner-directed, tuned by the nervous system and the adrenal hormones, but aware in a sense closer to human consciousness than, say, a hungry lizard’s instinctive snap at a passing beetle. Using past events as a framework, the large mammal predator is working out a relationship between movement and food, sensitive to possibilities in cold trails and distant sounds— and yesterday’s unforgotten lessons. The herbivore prey is of a different mind. Its 35 mood of wariness rather than searching and its attitude of general expectancy instead of anticipating are silk-thin veils of tranquillity over an explosive endocrine system.

Rabbit_Carrot

Most recent work on the history of leisure in Europe has been based on the central hypothesis of a fundamental discontinuity between preindustrial and industrial soci-eties. According to this view, the modern idea of leisure did not exist in medieval and early modern Europe: the modern distinction between the categories of work and leisure was a product of industrial capitalism. Preindustrial societies had festivals (together with informal and irregular breaks from work), while industrial societies have leisure in the form of weekends and vacations. The emergence of leisure is there-fore part of the process of modernization. If this theory is correct, there is what Michel Foucault called a conceptual rupture between the two periods, and so the very idea of a history of leisure before the Industrial Revolution is an anachronism.

To reject the idea that leisure has had a continuous history from the Middle Ages to the present is not to deny that late medieval and early modern Europeans engaged in many pursuits that are now commonly considered leisure or sporting activities— jousting, hunting, tennis, card playing, travel, and so on—or that Europe in this period was dominated by a privileged class that engaged in these pursuits. What is involved in the discontinuity hypothesis is the recognition that the people of the Middle Ages and early modern Europe did not regard as belonging to a common category activities (hunting and gambling, for example) that are usually classified together today under the heading of leisure. Consider fencing: today it may be considered a “sport,” but for the gentleman of the Renaissance it was an art or science. Conversely, activities that today may be considered serious, notably warfare, were often described as pastimes.

Serious pitfalls therefore confront historians of leisure who assume continuity and who work with the modern concepts of leisure and sport, projecting them back ontothe past without asking about the meanings contemporaries gave to their activities.

However, the discontinuity hypothesis can pose problems of its own. Historians hold-ing this view attempt to avoid anachronism by means of a simple dichotomy, cutting European history into two eras, preindustrial and industrial, setting up the binary opposition between a “festival culture” and a “leisure culture.” The dichotomy remains of use insofar as it reminds us that the rise of industrial capitalism was not purely a phenomenon of economic history, but had social and cultural preconditions and consequences. The dichotomy, however, leads to distortions when it reduces a great variety of medieval and early modern European ideas, assumptions, and practices to the simple formula implied by the phrase “festival culture.”