The World

Kategorie: Angličtina (celkem: 879 referátů a seminárek)

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  • Přidal/a: anonymous
  • Datum přidání: 23. února 2007
  • Zobrazeno: 1883×

Příbuzná témata

The World

Scientists believe that about 4.7 billion years ago, a swirling interstellar cloud of gas and dust began to fragment and form clusters that eventually became the Sun, Earth, and the other planets of our Solar System. On Earth, gravity, collisions with other bodies, and the radioactivity of some of the heavier elements caused the planet to begin melting. Lighter compounds floated outwards to form the Earth’s mantle and crust, while the heavier elements, mainly iron and nickel, sank in towards the centre to form the core. The resulting world was not quite a perfect sphere, and it remains slightly flattened today, thicker at the Equator than at the poles.

Once the planet was formed, volcanic eruptions caused light, volatile gases and vapours to escape from the mantle and crust. Some of these, primarily carbon dioxide and nitrogen, were captured by the Earth’s gravity and formed a primitive atmosphere, while water vapour condensed to form the world’s first oceans. Today water covers nearly 71 per cent of the world’s surface, and most of that forms the Pacific, Atlantic, and Indian oceans. The remaining 29 per cent of the Earth’s surface is covered by land, most of it concentrated on seven continents—Asia, Africa, North America, South America, Antarctica, Europe, and Australia.

About 3.5 billion years ago, conditions developed in which it was possible for life to emerge. The world’s oceans and atmosphere, affected by the proliferation and evolution of early life-forms, underwent major transformations, many of which would later enable the evolution of higher life-forms. Since then, life has evolved from simple single-celled organisms into the micro-organisms, insects, plants, and animals we know today. The world’s atmosphere has evolved as well, both influencing and influenced by the life-forms living within it

Anthropologists estimate that the first modern members of our species, Homo sapiens, appeared about 100,000 years ago in southeastern Africa. They then migrated, spreading rapidly across Africa and northeast into Asia, using their intelligence and dexterity to adapt to different environments. About 70,000 years later humans had colonized Europe, Australia, and North America. Humanity occupied most of the world’s landmasses as early as 10,000 years ago, with the exception of several remote islands and the continent of Antarctica.

Today humans have visited every bit of dry land in the world, and have colonized all but the most inaccessible and desolate regions. The human population now stands at about 6 billions.

As humanity spread across the world, geographically separate groups of humans developed distinctive physical features. Scientists believe these features were adaptations to local environmental conditions such as temperature, elevation, diseases, and dietary resources. People of different racial origin often exhibit differences in blood groups and blood serum proteins, body size and build, dental characteristics, hair form and coverage, shape of face and facial features, and skin, hair, and eye colour. Although it took tens of thousands of years in relative isolation for these distinctive adaptations to emerge, modern lifestyles, technology, and mobility have almost eliminated their role in biological survival.

Important distinctions between people in different geographic areas still exist, however. No longer primarily based upon environmental conditions, modern groupings may be based on language, culture, nationality, religion, and economics. Geographers have found that the human world can be classified into groups at many different levels. The largest and most frequently used geographic groupings are called regions and states. States are easiest to define because they are based on the political boundaries of the world’s 190 or so nations. Some states have a clear geographic identity, being inhabited by people of similar racial and linguistic origin, all participating in a common economic and cultural system. In other cases, one state may include groupings of people with diverse backgrounds who operate within isolated social and economic environments.

Regions—which are sometimes difficult to depict accurately on maps—may be based on economic activity, climate and topography, cultural history, or location relative to other regions. One region may be defined in terms of the vast desert that dominates its landscape, whilst another may exist because its residents follow a common religion and speak one language, or be dependent on a single agricultural crop. Many regions cross national borders, but others exist entirely within a single state. Despite the difficulties in defining regions precisely, they are extremely useful to geographers because they are based on the meaningful social, cultural, and economic factors that produce a distinctive geographic identity.

The world contains a multitude of resources and commodities.

Some, such as water and vegetables, are essential for human life. Others, such as iron and coal, are particularly useful to human beings. A few resources, including gold and uranium, are more valuable because they are scarce. Others, such as sand or air, are widely available and have a correspondingly low exchange value. The relative value of a commodity is dependent on two factors—how much of it there is and how much it is wanted. Economists call this the law of supply and demand. Commodities are often acquired where they are abundant and cheap and transported to regions where they are scarce and expensive, being exchanged there for valuable goods and services.

The human world today can be viewed as a vast network in which people produce, transport, exchange, and consume resources, commodities, and even ideas. While one region produces grain, another produces petroleum, and a third manufactures heavy machinery. Each depends on the products of the other two. Residents of each region seek to maximize the value of their own products and to obtain the products and resources they lack for the lowest possible price. Some regions are extremely active within this world system, maintaining vigorous trading relationships with every region willing to participate. Others are almost isolated from it, engaging in limited trade with only one or two neighbouring regions.

Since its creation, the world has developed into an increasingly complex system. All the world’s life forms are part of that system, consuming and producing resources in various ways. Humanity is also part of this system, and advancing technology has expanded the role of human activity in the world system. Unlike other inhabitants of the planet, however, humanity has become uniquely aware of its surroundings. As human understanding of the world expands, our ability to observe patterns and trends, and to predict future developments, is enhanced. This knowledge gives us the power to make decisions based not only on our immediate needs, but also on the probable future impact of our actions. In order to improve our ability to make good decisions, it is important for each of us to learn as much as we can about the world and the people with whom we share it.

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