Topic 30: Environments

Vegetables are parts of (1) __________ that are consumed by humans or other animals as food. The original meaning is still commonly used and is applied to plants collectively to refer to all edible plant matter, (2) __________ the flowers, fruits, stems, leaves, roots, and seeds. Originally, vegetables were collected from the wild by hunter-gatherers and entered cultivation in several parts of the world, probably during the period 10,000 BC to 7,000 BC, when a new agricultural way of life developed. At first, plants which grew locally would have been cultivated, but as time went on, trade brought exotic crops from (3)__________ to add to domestic types. Nowadays, most vegetables are grown all over the world as climate permits.

Crops may be cultivated in protected environments in less suitable locations, and global trade in (4) __________ products allows consumers to purchase vegetables grown in faraway countries. The scale of production varies from subsistence farmers supplying the needs of their family for food, to agribusinesses with vast areas of single-product crops. Depending on the type of vegetable concerned, harvesting the crop is followed by grading, storing, processing, and marketing. Vegetables can be eaten (5) __________ raw or cooked and play an important role in human nutrition, being mostly low in fat and carbohydrates, but high in vitamins, minerals and dietary fiber. Many nutritionists encourage people to consume plenty of fruit and vegetables, five or more portions a day often being recommended.

The “balance of nature” is not an empty phrase. Nature provides a population to occupy a suitable environment and cuts down surplus on population to fit the available food supply. One means of reducing surplus population is predators; others are parasites and diseases. Also, population density produces nervous disorders and even drivers animals to mass migrations, like the lemmings of Norway who plunge into the sea.

That predator populations increase to control other animals has long been known. Many years ago, the Hudsons Bay Company records revealed that the fox population went up and down about a year after the rabbit population had gone up and down.

Sometimes a situation occurs in which the predator population is reduced to a level below that which nature can readily replace. On Valcour Island in Lake Champlain (New York), a costly campaign resulted in the elimination of predatory animals only to have birds and small animals (including grouse and hares, popular game) increase for four years afterward. Then, lacking predator control, nature resorted to disease to cut down on these populations.

Jamaica had an example of natures persistence in providing animals for existing habits. Sugar planters, about 75 years ago, imported mongooses to control rats. The mongooses killed off the rats and, with plentiful food, multiplied. Rats became scarce and the mongooses ate lambs, puppies, and wildlife. Eventually, food became scarce and the mongooses’ population declined.

Trees are useful to man in three very important ways: they provide him with wood and other products; they give him shade; and they help to prevent droughts and floods.

Unfortunately, in many parts of the world, man has not realized that the third of these services is the most important. In his eagerness to draw quick profit from the trees, he has cut them down in large numbers.

Two thousand years ago, a rich and powerful country cut down its trees to build warships, with which to gain itself an empire. It gained the empire but, without its trees, its soil became bare and poor. When the empire fell to pieces, the country found itself faced by floods and starvation.

Even though government realizes the importance of a plentiful supply of trees, it is difficult sometimes to make the people realize this. They cut down the trees but are too careless to plant and look after new trees. So, unless the government has a good system of control, or can educate the people, the forests will slowly disappear.

This does not only mean that there will be fewer trees. The results are even more serious: for where there are trees, their roots break the soil up, allowing the rain to sink in, and also bind the soil. This prevents the soil from being washed away. But where there are no trees, the rain falls on hard ground and flows away on the surface, and this causes floods and the rain carries away the rich topsoil in which crops grow. When all the topsoil is gone, nothing remains but worthless desert.

(Source: www.cmr.com.cn/teach/tongkao/tksV200505_dxyyb_st.doc)

Scientists have uncovered a new threat to the world’s endangered coral reefs. They have found that most are incapable of growing quickly enough to compensate for rising sea levels triggered by global warming. The study suggests that reefs – which are already suffering serious degradation because the world’s seas are warming and becoming more acidic – could also become overwhelmed by rising oceans.

The research – led by scientists at Exeter University and published in Nature this week – involved studying growth rates for more than 200 tropical western Atlantic and Indian Ocean reefs. It was found only 9% of these reefs had the ability to keep up with even the most optimistic rates of sea-level rises forecast by the Intergovernmental Panel on Climate Change. “For many reefs across the Caribbean and Indian Ocean regions, where the study focused, rates of growth are slowing due to coral reef degradation,” said Professor Chris Perry, of Exeter University. “Meanwhile, rates of sea-level rise are increasing – and our results suggest reefs will be unable to keep up. As a result, water depths above most reefs will increase rapidly through this century.”

Sea levels rose by several inches over the past century and measurements indicate the speed of this increase is now rising significantly. Two key factors are involved: climate change is making ocean water warmer and so it expands. And as ice sheets and glaciers melt, they increase amounts of water in the oceans.

At the same time, reefs are being weakened by ocean warming and also by ocean acidification, triggered as the seas absorb more and more carbon dioxide. These effects lead to bleaching events that kill off vast stretches of coral and limits their ability to grow.

“Our predictions, even under the best case scenarios, suggest that by 2100, the inundation of reefs will expose coastal communities to significant threats of shoreline change,” said co-author Prof Peter Mumby of Queensland University. This point was backed by US marine scientist Ilsa Kuffner writing in a separate comment piece for Nature. “The implications of the study are dire. Many island nations and territories are set to quickly lose crucial natural resources.”

(Source: https://www.theguardian.com/)

Far from being barren wastelands, deserts are biologically rich habitats with a vast array of animals and plants that have adapted to the harsh conditions there. Some deserts are among the planet’s last remaining areas of total wilderness. Yet more than one billion people, one-sixth of the Earth’s population, actually live in desert regions.

Deserts cover more than one fifth of the Earth’s land, and they are found on every continent. A place that receives less than 10 inches (25 centimeters) of rain per year is considered a desert. Deserts are part of a wider classification of regions called “dry lands.” These areas exist under a moisture deficit, which means they can frequently lose more moisture through evaporation than they receive from annual precipitation.

And despite the common conceptions of deserts as dry and hot, there are cold deserts as well. The largest hot desert in the world, northern Africa’s Sahara, reaches temperatures of up to 122 degrees Fahrenheit (50 degrees Celsius) during the day. But some deserts are always cold, like the Gobi desert in Asia and the desert on the continent of Antarctica. Others are mountainous. Only about 10 percent of deserts are covered by sand dunes. The driest deserts get less than half an inch (one centimeter) of precipitation each year, and that is from condensed fog not rain.

Desert animals have adapted ways to help them keep cool and use less water. Camels, for example, can go for days without food and water. Many desert animals are nocturnal, coming out only when the brutal sun has descended to hunt. Some animals, like the desert tortoise in the south-western United States, spend much of their time underground. Most desert birds are nomadic, crisscrossing the skies in search of food. Because of their very special adaptations, desert animals are extremely vulnerable to introduced predators and changes to their habitat.

Some of the world’s semi-arid regions are turning into desert at an alarming rate. This process, known as “desertification,” is not caused by drought, but usually arises from the demands of human populations that settle on the semi-arid lands to grow crops and graze animals. The pounding of the soil by the hooves of livestock may degrade the soil and encourage erosion by wind and water.

Because the low latitudes of the Earth, the areas near the equator, receive more heat than the latitudes near the poles, and because the nature of heat is to expand and move, heat is transported from the tropics to the middle and high latitudes. Some of this heat is moved by winds and some by ocean currents, and some gets stored in the atmosphere in the form of latent heat. The term “latent heat” refers to the energy that has to be used to convert liquid water to water vapor. We know that if we warm a pan of water on a stove, it will evaporate, or turn into vapor, faster than if it is allowed to sit at room temperature. We also know that if we hang wet clothes outside in the summertime they will dry faster than in winter, when temperatures are colder. The energy used in both cases to change liquid water to water vapor is supplied by heat – supplied by the stove in the first case and by the Sun in the latter case. This energy is not lost. It is stored in water vapor in the atmosphere as latent heat. Eventually, the water stored as vapor in the atmosphere will condense to liquid again, and the energy will be released to the atmosphere.

In the atmosphere, a large portion of the Sun’s incoming energy is used to evaporate water, primarily in the tropical oceans. Scientists have tried to quantify this proportion of the Sun’s energy. By analyzing temperature, water vapor, and wind data around the globe, they have estimated the quantity to be about 90 watts per square meter, or nearly 30 percent of the Sun’s energy. Once this latent heat is stored within the atmosphere, it can be transported, primarily to higher latitudes, by prevailing, large-scale winds. Or it can be transported vertically to higher levels in the atmosphere, where it forms clouds and subsequent storms, which then release the energy back to the atmosphere.

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Hidden beneath the waves of the Tyrrhenian Sea near southwestern Italy lies a newfound volcanic mosaic dotted with geothermal chimneys and flat-topped seamounts. This complex is new to both science and the planet, geologically speaking; it’s only about 780,000 years old. Scientists aren’t particularly surprised to find volcanism in the region, which is home to active volcanoes like Mount Vesuvius and Mount Etna. But the new complex is unusual because it was created by a rare kind of fault, said study leader Fabrizio Pepe.

The western Mediterranean is seismically restless because of the collision of three tectonic plates: the African, the Eurasian and the Anatolian. Making matters more complex is a small chunk of crust called the Adriatic-Ionian microplate, which broke off of the African Plate more than 65 million years ago and is now being pushed under the larger Eurasian Plate in a process called subduction. Previously, scientists discovered a series of undersea volcanic arcs created by this tectonic unrest, starting near the Sardinian coast, with increasingly younger arcs southward and eastward. These arcs were like an arrow pointing ever farther eastward, prompting Pepe and his colleagues to search for an even younger arc about 9 miles off the coast of Calabria.

There, based on seafloor mapping, seismic data and magnetic anomalies, the researchers found a 772-square-mile region of lava flows, volcanic mountains and hydrothermal chimneys; vents in the seafloor allow hot minerals to spew out and form chimney-like structures. They dubbed the new area the Diamante‐Enotrio‐Ovidio Volcanic‐Intrusive Complex, after three flat-topped seamounts that dominate the seafloor. Those fractures are what allowed magma to rise to the surface at the Diamonte-Enotrio-Ovidio complex, creating an undersea landscape of lava flows and mountainous volcanoes. These volcanic seamounts are now plateaus because they protruded from the ocean when the sea level was lower, and they eroded into their present, flat-topped shape, Pepe said.

The volcanic complex is inactive, but there are small intrusions of lava in some parts of the seafloor there. However, the area could become active in the future, Pepe said, and active volcanism is ongoing on the eastern side of the Tyrrhenian Sea. The researchers are working to build a volcanic risk map of the complex to better understand if it could endanger human life or property. They are also investigating the possibility of tapping the complex to produce geothermal energy.

(Source: https://www.sciencedaily.com/)