FACTS ABOUT EARTH

 EARTH

The Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth’s gravity interacts with other objects in space, especially the Sun and the Moon, Earth’s only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. EARTH’S ATMOSPHERE Earth’s atmosphere is the layer of gases, commonly known as air, that surrounds the planet Earth and is retained by Earth’s gravity. The atmosphere of Earth protects life on Earth by creating pressure allowing for liquid water to exist on the Earth’s surface, absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation). EARTH’S OCEANS Earth’s oceans cover more than 70% of the planet’s surface, contain 97% of the planet’s water, and form the largest ecosystem on Earth. The oceans are the habitat of 230,000 known species, but because much of the ocean is unexplored, the number of species that exist in the oceans is much larger, possibly over two million. The vast majority of marine life is microbial. The oceans are divided into five basins: the Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern Ocean, and Arctic Ocean. EARTH’S CONTINENTS Earth’s seven continents are Africa, Antarctica, Asia, Australia, Europe, North America, and South America. EARTH’S GEOLOGY Earth’s outer solid layer, the lithosphere, is divided into the crust and the mantle. The crust is underlain by the mantle. The upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity. The crust of the Earth is composed of a great variety of igneous, metamorphic, and sedimentary rocks. The crust is underlain by the mantle. The upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity. EARTH’S ECOLOGY Earth’s biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the wide variety of life to exist. The biosphere is the global sum of all ecosystems. The two main types of ecosystems are terrestrial and aquatic ecosystems. Terrestrial ecosystems cover approximately 30% of Earth’s surface and are represented by forests, grasslands, and deserts. Aquatic ecosystems cover approximately 70% of Earth’s surface and are divided into marine ecosystems and freshwater ecosystems. Marine ecosystems cover approximately 3% of Earth’s surface and contain approximately 97% of Earth’s water. They are distinguished from freshwater ecosystems by the presence of dissolved compounds, especially salts. Earth’s lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth’s surface is covered with salt-water oceans. The remainder consists of continents and islands, with most of the inhabited land in the Northern Hemisphere. Earth has evolved through geological and biological processes that have left traces of the original conditions. EARTH’S LIFE The vast majority of life on Earth is microbial. Earth’s biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the wide variety of life to exist. The biosphere is the global sum of all ecosystems. The two main types of ecosystems are terrestrial and aquatic ecosystems. Terrestrial ecosystems cover approximately 30% of Earth’s surface and are represented by forests, grasslands, and deserts. Aquatic ecosystems cover approximately 70% of Earth’s surface and are divided into marine ecosystems and freshwater ecosystems. Marine ecosystems cover approximately 3% of Earth’s surface and contain approximately 97% of Earth’s water. They are distinguished from freshwater ecosystems by the presence of dissolved compounds, especially salts.

EARTH’S HUMANS The human species’ use of technology began with the conversion of natural resources into simple tools. The prehistoric discovery of how to control fire and the later Neolithic Revolution increased the available sources of food and the invention of the wheel helped humans to travel in and control their environment. Developments in historic times, including the printing press, the telephone, and the Internet, have lessened physical barriers to communication and allowed humans to interact freely on a global scale. The steady progress of military technology has brought weapons of ever-increasing destructive power, from clubs to nuclear weapons. Scientific advances and the discovery of new principles later allowed for powered flight and advancements in medicine, chemistry, physics, and engineering. EARTH’S MOON The Moon is an astronomical body that orbits Earth, being Earth’s only permanent natural satellite. The Moon is thought to have formed not long after Earth. The most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia. The Moon is in synchronous rotation with Earth, always showing the same side to Earth, the near side. The far side of the Moon, which is not visible from Earth, is often called the “dark side”, a label discouraged by many scientists. The Moon is believed to have originated 4.51 billion years ago, not long after Earth. The most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia. MOON’S GEOLOGY The Moon is a differentiated body: it has a geochemically distinct crust, mantle, and core. The crust is composed primarily of anorthositic plagioclase feldspar (with smaller amounts of mafic minerals such as the pyroxenes and olivine) and is some 60 km (37 mi) thick. Underneath the relatively thin crust is the lunar mantle, a denser silicate rock. Finally, the core is believed to be made of metallic iron with about 10% sulfur and traces of lighter elements. MOON’S EXPLORATION Robotic missions, including the Soviet Luna program, Ranger and Surveyor project, and Soviet Lunokhod project, sent unmanned probes to photograph the lunar surface. The Apollo program continued the American manned exploration of the Moon both by landings and by orbital missions between 1968 and 1972. The Apollo program included the first manned landings on the Moon in July 1969. The first Apollo landing site was in a lunar mare called Tranquillitatis, Latin for “serenity” or “quietness”, on July 20, 1969 (UTC). The crew of Apollo 11, Neil Armstrong and Buzz Aldrin, became the first men to walk on the lunar surface, while Michael Collins orbited above. FUTURE OF THE MOON The exploration of the Moon is an ongoing human activity, with the near-term goal of extending human settlement beyond Earth. The Moon is the only astronomical body that human beings have sent robotic probes to land on, and the only astronomical body that human beings have set foot upon. There are currently no plans for any manned missions to the Moon, although a number of private companies and countries have proposed such plans. EARTH’S OTHER MOONS The Moon is an astronomical body that orbits Earth, being Earth’s only permanent natural satellite. The Moon is thought to have formed not long after Earth. The most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia. The Moon is in synchronous rotation with Earth, always showing the same side to Earth, the near side. The far side of the Moon, which is not visible from Earth, is often called the “dark side”, a label discouraged by many scientists. EARTH’S RINGS Earth’s rings are a system of numerous particles, ranging in size from microscopic dust to moonlets several meters across, that orbit Earth. They are made of ice crystals, rocky debris, and dust. Two main rings, an inner ring and an outer ring, surround Earth. A third ring is surrounded by the inner ring, and a fourth ring is surrounded by the outer ring. The rings are extremely thin: most are less than 10 meters thick, with a maximum thickness of about one kilometer. EARTH’S DYNAMICS The Earth’s rotation is an example of a dynamical system that shows chaotic behavior. The Earth’s spin axis precesses slowly, with a period of 25,772 years. Earth’s obliquity (the angle between the plane of the equator and the plane of the ecliptic) also changes slowly over time, with a period of 41,000 years. The combination of the two precessions leads to a chaotic behavior of the Earth’s spin axis. The Earth’s spin axis is not a fixed point in space, but wanders in a cone with a base that is about 20 meters wide at the Earth’s surface. The Earth’s axial tilt (obliquity) also changes slowly over time, with a period of 41,000 years. The combination of the two precessions leads to a chaotic behavior of the Earth’s spin axis.

EARTH SUPERITIES

1. highest mountain peak: Mount Everest (29,035 feet or 8,848 meters) 2. largest desert: Sahara 3. deepest ocean trench: Mariana Trench (36,070 feet or 11,033 meters) 4. driest place: Atacama Desert in Chile 5. wettest place: Mawsynram, India 6. windiest place: Commonwealth Bay, Antarctica 7. coldest place: Vostok Station, Antarctica 8. hottest place: Lut Desert, Iran 9. oldest rocks: Isua Greenstone Belt in Greenland 10. deepest lake: Baikal in Siberia 11. largest lake: Caspian Sea 12. oldest city: Damascus, Syria 13. largest city: Tokyo, Japan 14. highest waterfall: Angel Falls in Venezuela 15. largest ice sheet: Antarctic Ice Sheet 16. largest island: Greenland 17. longest river: Nile (4,132 miles or 6,650 kilometers) 18. deepest river: Congo (2,920 feet or 890 meters) 19. largest forest: Amazon 20. largest desert: Sahara

FACTS ABOUT EARTH - Earth is the third planet from the Sun. - Earth is the only planet in the Solar System not named after a god. - Earth is the densest planet in the Solar System. - The diameter of Earth is about 12,700 kilometers (7,900 miles). - The mass of Earth is about 5.972 × 1024 kilograms, which is about 3/4 the mass of the Sun. - The gravity of Earth is about 9.81 m/s2, which is about the same as the Sun's gravity. - The surface temperature of Earth ranges from about -88 to 58 degrees Celsius (-129 to 136 degrees Fahrenheit). - The atmosphere of Earth is made up of 78% nitrogen, 21% oxygen, and 1% other gases. - The oceans of Earth are made up of 96.5% water, 2.5% salt, and 1% other dissolved materials. - The landmasses of Earth are made up of about 29% land, 71% water, and 1% ice. - There are about 7.2 billion people living on Earth.