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 Song” – by Michael Jackson
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.
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. All people today are classified as Homo sapiens * and according to the U.N. there is a grand total of 195 sovereign states ** 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.
Two hundred years ago the World Population was just over one billion. Since then the number of people on the planet grew more than 7-fold to 7.8 billion in 2020. Here’s a presumably reasonable forecast: Pop 2050 (mil) = 9,735; Pop 2100 (mil) = 10,875. About two thirds of the predicted growth in population between 2020 and 2050 will take place in Africa.
As for the maximum population the Earth can sustain, a 2012 U.N. report summarised 65 different estimated maximum sustainable population sizes. The most common estimate was eight billion, a little larger than the current population. But the estimates ranged from as few billions to, in one study, a staggering 1,024 billion.
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