Globally, the 20th century was marked by: two devastating world wars; the Great Depression of the 1930s; the end of vast colonial empires; rapid advances in science and technology, from the first airplane flight to the landing on the moon; the Cold War between the Western alliance and the Warsaw Pact nations; a sharp rise in living standards in North America, Europe, and Japan; increased concerns about the environment, including loss of forests, shortages of energy and water, the decline in biological diversity, and air pollution; the onset of the AIDS epidemic; and the ultimate emergence of the US as the only world superpower.The planet's population continues to explode: from 1 billion in 1820, to 2 billion in 1930, 3 billion in 1960, 4 billion in 1974, 5 billion in 1988, and 6 billion in 2000. For the 21st century, the continued exponential growth in science and technology raises both hopes (e.g., advances in medicine) and fears (e.g., development of even more lethal weapons of war).Geography WorldArea:total: 510.072 million sq kmland: 148.94 million sq kmwater: 361.132 million sq kmnote: 70.8% of the world's surface is water, 29.2% is landArea - comparative:land area about 16 times the size of the USLand boundaries:the land boundaries in the world total 250,708 km (not counting shared boundaries twice); two nations, China and Russia, each border 14 other countriesnote: 44 nations and other areas are landlocked, these include: Afghanistan, Andorra, Armenia, Austria, Azerbaijan, Belarus, Bhutan, Bolivia, Botswana, Burkina Faso, Burundi, Central African Republic, Chad, Czech Republic, Ethiopia, Holy See (Vatican City), Hungary, Kazakhstan, Kyrgyzstan, Laos, Lesotho, Liechtenstein, Luxembourg, Macedonia, Malawi, Mali, Moldova, Mongolia, Nepal, Niger, Paraguay, Rwanda, San Marino, Serbia, Slovakia, Swaziland, Switzerland, Tajikistan, Turkmenistan, Uganda, Uzbekistan, West Bank, Zambia, Zimbabwe; two of these, Liechtenstein and Uzbekistan, are doubly landlockedCoastline:356,000 kmnote: 98 nations and other entities are islands that border no other countries, they include: American Samoa, Anguilla, Antigua and Barbuda, Aruba, Ashmore and Cartier Islands, The Bahamas, Bahrain, Baker Island, Barbados, Bassas da India, Bermuda, Bouvet Island, British Indian Ocean Territory, British Virgin Islands, Cape Verde, Cayman Islands, Christmas Island, Clipperton Island, Cocos (Keeling) Islands, Comoros, Cook Islands, Coral Sea Islands, Cuba, Cyprus, Dominica, Europa Island, Falkland Islands (Islas Malvinas), Faroe Islands, Fiji, French Polynesia, French Southern and Antarctic Lands, Glorioso Islands, Greenland, Grenada, Guam, Guernsey, Heard Island and McDonald Islands, Howland Island, Iceland, Isle of Man, Jamaica, Jan Mayen, Japan, Jarvis Island, Jersey, Johnston Atoll, Juan de Nova Island, Kingman Reef, Kiribati, Madagascar, Maldives, Malta, Marshall Islands, Martinique, Mauritius, Mayotte, Federated States of Micronesia, Midway Islands, Montserrat, Nauru, Navassa Island, New Caledonia, New Zealand, Niue, Norfolk Island, Northern Mariana Islands, Palau, Palmyra Atoll, Paracel Islands, Philippines, Pitcairn Islands, Puerto Rico, Reunion, Saint Helena, Saint Kitts and Nevis, Saint Lucia, Saint Pierre and Miquelon, Saint Vincent and the Grenadines, Samoa, Sao Tome and Principe, Seychelles, Singapore, Solomon Islands, South Georgia and the South Sandwich Islands, Spratly Islands, Sri Lanka, Svalbard, Tokelau, Tonga, Trinidad and Tobago, Tromelin Island, Turks and Caicos Islands, Tuvalu, Vanuatu, Virgin Islands, Wake Island, Wallis and Futuna, TaiwanMaritime claims:a variety of situations exist, but in general, most countries make the following claims measured from the mean low-tide baseline as described in the 1982 UN Convention on the Law of the Sea: territorial sea - 12 nm, contiguous zone - 24 nm, and exclusive economic zone - 200 nm; additional zones provide for exploitation of continental shelf resources and an exclusive fishing zone; boundary situations with neighboring states prevent many countries from extending their fishing or economic zones to a full 200nmClimate:a wide equatorial band of hot and humid tropical climates - bordered north and south by subtropical temperate zones - that separate two large areas of cold and dry polar climatesTerrain:the greatest ocean depth is the Mariana Trench at 10,924 m in the Pacific OceanElevation extremes:lowest point: Bentley Subglacial Trench -2,540 mnote: in the oceanic realm, Challenger Deep in the Mariana Trench is the lowest point, lying -10,924 m below the surface of the Pacific Oceanhighest point: Mount Everest 8,850 mNatural resources:the rapid depletion of nonrenewable mineral resources, the depletion of forest areas and wetlands, the extinction of animal and plant species, and the deterioration in air and water quality (especially in Eastern Europe, the former USSR, and China) pose serious long-term problems that governments and peoples are only beginning to addressLand use:arable land: 13.31%permanent crops: 4.71%other: 81.98% (2005)Irrigated land:2,770,980 sq km (2003)Natural hazards:large areas subject to severe weather (tropical cyclones), natural disasters (earthquakes, landslides, tsunamis, volcanic eruptions)Environment - current issues:large areas subject to overpopulation, industrial disasters, pollution (air, water, acid rain, toxic substances), loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, soil degradation, soil depletion, erosionGeography - note:the world is now thought to be about 4.55 billion years old, just about one-third of the 13-billion-year age estimated for the universePeople WorldPopulation:6,525,170,264 (July 2006 est.)Age structure:0-14 years: 27.4% (male 919,219,446/female 870,242,271)15-64 years: 65.2% (male 2,152,066,888/female 2,100,334,722)65 years and over: 7.4% (male 213,160,216/female 270,146,721)note: some countries do not maintain age structure information, thus a slight discrepancy exists between the total world population and the total for world age structure (2006 est.)Median age:total: 27.6 yearsmale: 27 yearsfemale: 28.2 years (2006 est.)Population growth rate:1.14% (2006 est.)Birth rate:20.05 births/1,000 population (2006 est.)Death rate:8.67 deaths/1,000 population (2006 est.)Sex ratio:at birth: 1.06 male(s)/femaleunder 15 years: 1.06 male(s)/female15-64 years: 1.03 male(s)/female65 years and over: 0.79 male(s)/femaletotal population: 1.01 male(s)/female (2006 est.)Infant mortality rate:total: 48.87 deaths/1,000 live birthsmale: 50.98 deaths/1,000 live birthsfemale: 46.65 deaths/1,000 live births (2006 est.)Life expectancy at birth:total population: 64.77 yearsmale: 63.16 yearsfemale: 66.47 years (2006 est.)Total fertility rate:2.59 children born/woman (2006 est.)HIV/AIDS - adult prevalence rate:NAHIV/AIDS - people living with HIV/AIDS:NAHIV/AIDS - deaths:NAReligions:Christians 33.03% (of which Roman Catholics 17.33%, Protestants 5.8%, Orthodox 3.42%, Anglicans 1.23%), Muslims 20.12%, Hindus 13.34%, Buddhists 5.89%, Sikhs 0.39%, Jews 0.23%, other religions 12.61%, non-religious 12.03%, atheists 2.36% (2004 est.)Languages:Mandarin Chinese 13.69%, Spanish 5.05%, English 4.84%, Hindi 2.82%, Portuguese 2.77%, Bengali 2.68%, Russian 2.27%, Japanese 1.99%, Standard German 1.49%, Wu Chinese 1.21% (2004 est.)note: percents are for "first language" speakers onlyLiteracy:definition: age 15 and over can read and writetotal population: 82%male: 87%female: 77%note: over two-thirds of the world's 785 million illiterate adults are found in only eight countries (India, China, Bangladesh, Pakistan, Nigeria, Ethiopia, Indonesia, and Egypt); of all the illiterate adults in the world, two-thirds are women; extremely low literacy rates are concentrated in three regions, South and West Asia, Sub-Saharan Africa, and the Arab states, where around one-third of the men and half of all women are illiterate (2005 est.)Government WorldAdministrative divisions:272 nations, dependent areas, and other entitiesLegal system:all members of the UN are parties to the statute that established the International Court of Justice (ICJ) or World CourtEconomy WorldEconomy - overview:Global output rose by 4.4% in 2005, led by China (9.3%), India (7.6%), and Russia (5.9%). The other 14 successor nations of the USSR and the other old Warsaw Pact nations again experienced widely divergent growth rates; the three Baltic nations continued as strong performers, in the 7% range of growth. Growth results posted by the major industrial countries varied from no gain for Italy