Earth

Earth, also known as Sol III or Terra, is the homeworld of the human species.

Geography
From space, Earth, the third planet in the Sol system, appears as a blue-green orb enveloped in a white web of clouds. Its surface has vast bodies of water and several large continents of varying climates. There were two polar ice caps at either end of the planet. Earth possessed seven continents: Africa, Asia, Europe, Australia, North America, South America, and Antarctica. These continents were separated by four massive oceans: the Atlantic, Pacific, Indian, and Arctic.

Earth possessed a large amount of native flora and fauna. Later on into its history, cities grew to become a dominant environment on the planet. Earth's cities widely varied in appearance, with most reflecting the natural climate they were constructed in: in general, port cities with access to bodies of water were larger than inland cities.

Prehistory
Earth first formed around 4,500,000,000 BC, and gave rise to its first single-celled organisms around 3,500,000,000 BC. Earth was unique among the other planets in the Sol system due to having evolved life and never having lost it; Mars also harbored life billions of years ago, and even oceans and seas, but these eventually faded away.

During an era called the Mesozoic, Earth was home to a diverse group of reptiles known as dinosaurs. These dinosaurs eventually receded due to a catastrophic extinction-level event which took place near the end of the Mesozoic, in the period known as the Cretaceous, in which a huge asteroid the size of Mount Everest slammed into the planet. While the resulting nuclear winter killed much of the planet's biosphere, some species of dinosaurs and other animals survived; the remaining groups of dinosaurs eventually became Earth's bird species. Despite the apocalyptic scale of death which followed the Cretaceous extinction event, life eventually recovered on the planet.

Rise of humanity
The ancestors of all species of human are descended from primates which evolved on the continent of Africa. There were a variety of other human species besides Homo sapiens, most of which inhabited other areas of the planet. With the extinction of Homo neanderthalensis, humanity, Homo sapiens, stood as the last extant member of the genus Homo. Beginning as hunter-gatherers, the species struggled on for hundreds of thousands of years, until civilizations began to form. Gradually, the civilizations became more and more sophisticated and technologically advanced, until it reached a point where humans had colonized every continent and were the dominant lifeforms on the planet.

By the year 1914, much of the human species was divided into two factions, the Triple Entente, or Allies: the United Kingdom, France, Russia, and later the United States of America, and the Triple Alliance, or Central Powers: Germany, Austria-Hungary, and other nations of similar ideals. The Central Powers were defeated at the end of World War I in 1918, resulting in a decade of prosperity for the Allies, followed by an economic depression and the rise of fascism, Nazism, and Communism in many countries. In 1939, another World War erupted, between the Allies (Britain, the Soviet Union, later the United States, and many other nations) and the Axis (Nazi Germany, fascist Italy, and the Empire of Japan). In 1945, the Allies defeated the Axis. Later that year, the victorious nations, in an attempt to prevent future World Wars, founded the United Nations, an international assembly of peaceful nations, whose goal was to settle international disputes peacefully. In 1957, humanity finally made their way into space with unmanned probes and by 1961, humans themselves had gone into space. In 1969, humanity had finally stepped on an extraterrestrial surface - Earth's moon, Luna.

After World War II, humanity would avoid fighting wars on that scale for a time, although smaller wars and conflicts erupted, including the Korean War, Vietnam War, Cold War, and the War on Terror. In the early 21st century, terrorism became a particularly noteworthy thorn in the side of the nations on Earth, and numerous small wars broke out along with civil unrest in many countries. However, no full wars on the same scale as past World Wars erupted until a full century later.

Ecological change
In response to the increasing human use of fossil fuels throughout the 18th, 19th, 20th, and 21st centuries, Earth's environment began to change rather rapidly. A thinning of the ozone layer in the late 20th and early 21st centuries also grew cause for concern, although the use of certain industrial chemicals was seen to be the cause, and this was quickly corrected. The effects of global warming, however, were not as easily corrected, as so many other sentient species would discover when their homeworlds began warming up. By 2010, the Earth's polar ice caps had begun to melt rapidly, leaving the fates of several species which inhabited them uncertain. In tandem, global sea levels also began to rise, along with an increase of the incidences of extreme weather such as tornadoes, hurricanes, and cyclones. Animal and plant species went extinct on levels unprecedented since the planet's earlier stages of development. The effects of global warming would continue to increase, growing so dire in the later half of the 21st century and the early part of the 22nd so as to spur interest in off-world colonization. Global warming would only be corrected with the invention of terraforming technology further on in humanity's development.