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In 2001 the BBC broadcast The Blue Planet, a series on the natural history of the world's oceans. It received critical acclaim, high viewing figures, audience appreciation ratings, and many awards. It also became a hugely profitable global brand, eventually being sold to 150 countries worldwide. Feedback showed that audiences particularly liked the epic scale, the scenes of new and unusual species and the cinematic quality of the series. Programme commissioners were keen for a follow-up, so Alastair Fothergill decided that the Natural History Unit should repeat the formula with a series looking at the whole planet. The idea for Planet Earth was born, and the series was commissioned by Lorraine Heggessey, then Controller of BBC One, in January 2002.[5]
"A hundred years ago, there were one and a half billion people on Earth. Now, over six billion crowd our fragile planet. But even so, there are still places barely touched by humanity. This series will take you to the last wildernesses and show you the planet and its wildlife as you have never seen them before."
"Our planet is still full of wonders. As we explore them, so we gain not only understanding, but power. It's not just the future of the whale that today lies in our hands: it's the survival of the natural world in all parts of the living planet. We can now destroy or we can cherish. The choice is ours."
Though we can't feel it, Earth zooms through its orbit at an average velocity of 18.5 miles a second. During this circuit, our planet is an average of 93 million miles away from the sun, a distance that takes light about eight minutes to traverse. Astronomers define this distance as one astronomical unit (AU), a measure that serves as a handy cosmic yardstick.
We also enjoy protection from Earth's magnetic field, generated by our planet's rotation and its iron-nickel core. This teardrop-shaped field shields Earth from high-energy particles launched at us from the sun and elsewhere in the cosmos. But due to the field's structure, some particles get funneled to Earth's Poles and collide with our atmosphere, yielding aurorae, the natural fireworks show known by some as the northern lights.
At the same time, telescopes are gazing outward to find other Earths. Thanks to instruments such as NASA's Kepler Space Telescope, astronomers have found more than 3,800 planets orbiting other stars, some of which are about the size of Earth, and a handful of which orbit in the zones around their stars that are just the right temperature to be potentially habitable. Other missions, such as the Transiting Exoplanet Survey Satellite, are poised to find even more.
From what we know so far, Earth is the only planet that hosts life and the only one in the Solar System with liquid water on the surface. Earth is also the only planet in the solar system with active plate tectonics, where the surface of the planet is divided into rigid plates that collide and move apart, causing earthquakes, mountain building, and volcanism. Sites of volcanism along Earth's submarine plate boundaries are considered to be potential environments where life could have first emerged.
Earth is the right distance from the sun, such that liquid water has been stable in significant volumes over much of the planet's lifetime. It has the right chemical ingredients for life (e.g. water and carbon), and chemical cycling (such as between the planet's interior and oceans by volcanism and other geological activity) provides chemical pathways for life to extract energy to survive.
Scientists estimated that 1 in 5 stars like our sun has one Earth-like planet orbiting around them, which may support life. Considering that there are more than 200 billion stars in our Milky Way, there might be an estimated 40 billion planets that might support life in our galaxy.
Earth is the only naturally habitable planet for complex (e.g. human) life in the solar system. The consequences of a warming climate are far-reaching and are already threatening some people's ways of life and damaging wider biodiversity. If Earth becomes uninhabitable we have nowhere else to go. Colonizing the Moon and Mars is no substitute for preserving Earth. The Moon and Mars cannot sustain Earth's population of humans and other organisms.
Earth, our home, is the third planet from the sun. While scientists continue to hunt for clues of life beyond Earth, our home planet remains the only place in the universe where we've ever identified living organisms.
Earth has a diameter of roughly 8,000 miles (13,000 kilometers) and is mostly round because gravity generally pulls matter into a ball. But the spin of our home planet causes it to be squashed at its poles and swollen at the equator, making the true shape of the Earth an "oblate spheroid."
Our planet is unique for many reasons, but its available water and oxygen are two defining features. Water covers roughly 71% of Earth's surface, with most of that water located in our planet's oceans. About a fifth of Earth's atmosphere consists of oxygen, produced by plants.
Earth's axis of rotation is tilted in relation to the ecliptic plane, an imaginary surface through the planet's orbit around the sun. This means the Northern and Southern Hemispheres will sometimes point toward or away from the sun depending on the time of year, and this changes the amount of light the hemispheres receive, resulting in the changing seasons.
Earth happens to orbit the sun within the so-called "Goldilocks zone," where temperatures are just right to maintain liquid water on our planet's surface. Earth's orbit is not a perfect circle, but rather a slightly oval-shaped ellipse, similar to the orbits of all the other planets in our solar system. Our planet is a bit closer to the sun in early January and farther away in July, although this proximity has a much smaller effect on the temperatures we experience on the planet's surface than does the tilt of Earth's axis.
Scientists think Earth was formed at roughly the same time as the sun and other planets some 4.6 billion years ago when the solar system coalesced from a giant, rotating cloud of gas and dust known as the solar nebula. As the nebula collapsed under the force of its own gravity, it spun faster and flattened into a disk. Most of the material in that disk was then pulled toward the center to form the sun.
"It was thought that because of these asteroids and comets flying around colliding with Earth, conditions on early Earth may have been hellish," Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, previously told Space.com.
Radioactive materials in the rock and increasing pressure deep within the Earth generated enough heat to melt the planet's interior, causing some chemicals to rise to the surface and form water, while others became the gases of the atmosphere. Recent evidence suggests that Earth's crust and oceans may have formed within about 200 million years after the planet took shape.
Earth's core is about 4,400 miles (7,100 km) wide, slightly larger than half the Earth's diameter and about the same size as Mars. The outermost 1,400 miles (2,250 km) of the core are liquid, while the inner core is solid. That solid core is about four-fifths as big as Earth's moon, at some 1,600 miles (2,600 km) in diameter. The core is responsible for the planet's magnetic field, which helps to deflect harmful charged particles shot from the sun.
Above the core is Earth's mantle, which is about 1,800 miles (2,900 km) thick. The mantle is not completely stiff but can flow slowly. Earth's crust floats on the mantle much as a piece of wood floats on water. The slow motion of rock in the mantle shuffles continents around and causes earthquakes, volcanoes and the formation of mountain ranges.
The strength of Earth's magnetic field decreased by about 90 percent when a field reversal occurred in ancient past, according to Andrew Roberts, a professor at the Australian National University. The drop makes the planet more vulnerable to solar storms and radiation, which could significantly damage satellites as well as communication and electrical infrastructure.
Earth's atmosphere is roughly 78 percent nitrogen and 21 percent oxygen, with trace amounts of water, argon, carbon dioxide and other gases. No other planet in the solar system has an atmosphere loaded with free oxygen, which is vital to one of the other unique features of Earth: life.
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