Earth (aka Gaia, Gaea, Terra, Tellus, the world, the globe) is the third planet from the Sun and the only astronomical object known to harbor life.
Earth’s moon is 2,159 miles (3,474 km) wide – about one fourth of Earth’s diameter. Our planet has one moon, while Mercury and Venus have none and all the other planets in our solar system have two or more. The leading explanation for how Earth’s moon formed is that a giant impact knocked the raw ingredients for the moon off the primitive, molten Earth and into orbit. Scientists have suggested that the object that hit the planet had roughly 10% the mass of Earth – about the size of Mars.
When the Solar System in The Universe settled into its current layout about 4.5 billion years ago, Earth formed when gravity pulled swirling gas and dust in to become the fifth largest of the planets in our solar system. Like its fellow terrestrial planets, Earth has a central core, a rocky mantle and a solid crust.
While the Earth was in its earliest stage (Early Earth), a giant impact collision with a planet-sized body named Theia is thought to have formed the Moon. The Hadean eon represents the time before a reliable (fossil) record of life. 4.5 billion years ago, it began with the formation of the planet and ended 4.0 billion years ago. Looking at it from about now, after 2 billion years, increased energy output from the Sun will boil Earth’s oceans, but the planet itself will survive.
Earth is composed of many elements, chief among them oxygen, silicon, magnesium, iron, aluminum and nickel. Our planet’s crust is a thin outer layer, containing mostly silicate and basaltic rocks that extends on average around 18 miles (30 km) below the planet’s surface. The mantle is the next layer down, extending to about 1,800 miles (2,900 km) below Earth’s surface. A common misconception is that all the rock in the mantle is melted into magma; in reality, most of it is in a highly viscous form that is so thick that it takes millions of years for its movement to become apparent. In Earth’s center is a nickel-iron core that is liquid on the outside down to 1,400 miles (2,250 km) but is crushed by incredible pressures into a solid form at the lowest depths.
Earth has several enormous landforms. The largest continent, which is sometimes known as Afro-Eurasia (though more commonly broken up into Africa, Europe and Asia) has a total area of 32.8 million square miles (84.95 million square km). The Americas (North and South America) together constitute 16.43 million square miles (42.55 million square km) while the frozen continent of Antarctica is 5.41 million square miles (14 million square km). The area of Australia is 2.97 million square miles (7.66 million square km).
Processes below Earth’s crust cause these continents to move around over geological time periods. Geologists have discovered underground continents buried deep below the surface and though nobody quite knows how or when they formed, they may be as old as Earth itself.
Consider the movement of the earth’s surface with respect to the planet’s center. The earth rotates once every 23 hours, 56 minutes and 4.09053 seconds, called the orbital period and its circumference is roughly 40,075 kilometers. Thus, the surface of the earth at the equator moves at a speed of 460 meters per second (1,656 kilometer per hour).
The earth is moving around our sun in a very nearly circular orbit. It covers this route at a speed of nearly 30 kilometers per second (110,000 kilometers per hour). In addition, our solar system – Sun, Earth and all that – moves through space at 20 kilometers per second (72,000 kilometers per hour) and whirls around the center of our galaxy at some 220 kilometers per second (792,000 kilometers per hour).
“Speeding? Wanna know what’s speeding? We are sitting on a ball traveling at 110,000 km/h trough space and its surface at the same time rotates at 1,656 km/h while the containing solar system moves through space at 72,000 km/h and whirls around its center at some 792,000 km/h. Now, that’s what I call speeding!”
– Eric Roth
What makes the Earth habitable? It is the right distance from the Sun, it is protected from harmful solar radiation by its magnetic field, it is kept warm by an insulating atmosphere, and Mother Nature has the right chemical ingredients for life, including water and carbon.
One of the earliest known humans is Homo Habilis, or “handy man,” who lived about 2.4 million to 1.4 million years ago in Eastern and Southern Africa. The World Population today consists of people classified as Homo Sapiens * and according to the U.N. there is a grand total of 195 sovereign states (Governments) ** in the world today.
* = Homo Sapiens most likely developed in the Horn of Africa between 300,000 and 200,000 years ago. The “recent African origin” model proposes that all modern non-African populations are substantially descended from populations of Homo sapiens that left Africa after that time.
** = International law defines sovereign states as having a permanent population, defined territory, one Government and the capacity to enter into relations with other sovereign states.