Alien Species


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"Mostly harmless."
The Hitchhiker's Guide to the Galaxy entry on Earth.
System Sol System
Moons Luna
Orbital position 3
Rotation period 23h 56m 4.0910s
Orbital period 365.25636 solar days
Class Terrestrial
Diameter 12756 km
Atmosphere 78% nitrogen
21% oxygen
0.9% argon
0.1% others (carbon dioxide, water, etc.)
Climate Many climate zones
Gravity 1 g (9.8 m/s²)
Primary terrain Forests, grasslands, deserts, jungles, wetlands, mountains, tundra, polar regions, oceans, lakes and rivers.
Surface water 71%
Native fauna Humans and an estimated 6.8 million other animal species, plus millions of assorted microorganisms.
Native flora Estimated 390 thousand plant species, plus millions of assorted microorganisms.
Behind the Scenes
Universe Real

Earth, a.k.a. Terra, Gaia or Sol III and referred to by many other names, is a medium-sized terrestrial planet and the third world orbiting the star Sol. It is orbited by a large, inhospitable moon known as Luna. Earth is perhaps best known for being the homeworld of the Human species, along with millions of other native lifeforms.


The Earth is believed to have been formed 4.5 billions of years ago, along with the rest of Sol's planetary system. During the course of its formation, it is believed that Earth collided with another planetary object, about the size of Mars, which resulted in the destruction of this object and the removal of a large chunk of the newborn Earth. This former portion of the planet stayed in orbit and eventually formed its moon, Luna.

After some half a billion years, Earth's surface cooled off, allowing for the formation of large oceans of liquid water. Some of the water had come to Earth via impacts of ice comets. The minerals dissolved in the oceans account for the sea salt. The first traces of life appeared soon afterwards. The planet's magnetic field is believed to have established itself about 3.5 billion years ago, helping to protect the ancient planet from solar radiation and other threats.

Exactly how life appeared on the planet is still a mystery. Some theories involve it having naturally evolved from complex chemical compounds in a primordial soup, this happening either near the ocean surface or near the hydrothermal sea vents in the deep sea, or still possibly in the atmosphere. Other theories state that life arrived on Earth from somewhere else, either naturally, as in the Panspermia Hypothesis; or with help from a sapient alien species, as in the Exogenesis Hypothesis.

Among the many sorts of unicellular creatures which evolved on Earth, some were phototrophs, using sunlight to perform photosynthesis, which involves the consumption of carbon dioxide and the ejection of free oxygen in the atmosphere. This oxygen was fatal for most of the lifeforms then, but some evolved to consume the new gas, using it for respiration. These oxygen-breathing microbes spread through the planet and gave origin to most of the extant earthling lifeforms.

During a poorly understood time period between 750 and 600 million years ago, the so-called Snowball Earth era, Earth was almost completely covered by water ice. It was only after this period, about 550 million years ago, that several multicellular animals evolved and spread in the world's oceans. Complex animals and plants later began to colonize the dry land at some point between 480 and 450 MYA.

During the last 400 million years, complex life underwent four major mass extinction events, with one of them, the Permian Extinction, resulting in the extinction of more than 90% of the planet's species. After that, a new group of reptiles emerged and some grew to enormous proportions. These creatures later became known as the dinosaurs and represent an iconic image of the prehistoric Earth. All of them, except for the bird family, were later eliminated by the next mass extinction, caused by a meteor impact 65 MYA. After the end of the dinosaurs' era the Earth was inherited mostly by mammals (although other vertebrate groups are also largely present, including birds, squamates, turtles, fish and amphibians). One mammalian species ended up developing ever increasing intelligence and technology and gave origin to the Human civilization. Although hotly debated, most scientists agree that many non-human animals have sapience to some extent. Among them, are all vertebrates and at least some invertebrates, such as cephalopods and arthropods.


Earth is the largest terrestrial planet of the Solar System and has the greatest density of any planet in the system as well. It is a geologically active planet, with an iron-nickel core surrounded by a mantle of liquid magma and covered by a cold rocky crust.

70% of the surface of Earth is covered by oceans of salt water. There are currently six main continents: North America, South America, Africa, Oceania, Antarctica and Eurasia. Some sources list Eurasia as two different continents: Europe and Asia; and some have the Americas taken together as one sole continent. Also, the lower portion of North America is sometimes called the Central America and treated as a continent on its own. However, all these views are mostly based on Human politics and sociology. Due to the constant movement of the continental plates, the continents' arrangement was different in each past period of Earth.

Earth also has two polar caps, one on the north, creating the frozen area known as the Arctic Ocean; and one on the south, blanketing the continent of Antarctica.

The atmosphere is composed of 78% nitrogen and 21% oxygen, which is produced by phototrophic lifeforms such as plants and phytoplankton. Several other elements are also present.

Fauna and floraEdit

All life on Earth is carbon-based and has a very complex biochemistry involving several chemical elements, notably hydrogen, oxygen, silicon and nitrogen.

Main groups of organisms on the planet include: virus, bacteria, archaea (also known as archaeobacteria) and eukaryotes. The last group is believed to have been formed by means of symbiogenesis between bacteria and archaea. Within the eukaryotes several complex organism groups are found, including the phototrophic algae and land plants, the decomposing fungi and the predatory animals. Single-celled eukaryotes are also notable for their variety of forms and lifestyles, but are usually clumped together in the artificial group known as protozoa, nevertheless.

Extraterrestrial affairsEdit

So far, Earth is the only place in the universe where life is known to exist, although this is most likely due to the technological difficulties in detecting lifeforms on other planets, or even in space vacuum, unless they showed themselves extremely close to Earth. According to our current knowledge it is perfectly conceivable that life may exist on several locations, either evolving there independently or spreading itself throughout the Universe, as dictates the hypothesis of Panspermia.

Several people across the Earth have related seeing alien spaceships (the so-called UFOs – Unidentified Flying Objects) or even interacting with aliens themselves. Some even believe that many extraterrestrials, belonging to such races as Greys or Reptoids, are secretly infiltrated in Human society. Many of these ufological reports have been proved as being either mistakes or hoaxes and the vast majority of scientists currently deny the possibility of alien visits or interactions with earthlings happening today. Some, however, like Erich von Däniken, have proposed that such encounters may have happened in the past, which would explain some of the world's supposed mysteries like the construction of enormous pyramids by allegedly primitive civilizations. These ideas too are largely denied by the scientific community due to the lack of evidences. The idea that some cryptic or mythological creatures, like the atmospheric beasts or the Chupacabras, may be of extraterrestrial origin has also been proposed by some.

Earth in various universesEdit

Spore Earth T3

A perfect T3 Earth as it appears in Maxis' SPORE.

Earth is definitely (and understandably) the planet most commonly featured in science-fiction media dealing with extraterrestrials, not always because of the planet itself, but rather because the presence of Humans – which are native to Earth, of course – provides the reader, viewer or player with a familiar element in the story.

Several sci-fi works feature Earth being visited, or invaded by sapient alien species of some sort. Others, set in the future, actually have Humans exploring other planets and regions and interacting with alien species of many sorts.

There are some examples of science-fiction works which do not mention Earth at all, most notably the Star Wars franchise, as well as the Walt Disney movie Treasure Planet, though both of which do feature Humans, without making mentions of the race's origins.

Sometimes Earth is portrayed as a thriving, highly developed, sometimes even near-utopian planet. In other universes, it is a nightmare world, often on the brink of or after an apocalypse.

This section is still incomplete. You can help Alien Species Wiki by adding the information that's missing.

3rd Rock from the Sun UniverseEdit

In this universe, Earth is very similar to its real-life counterpart. The main difference is that the planet is known to the Solomon family's race (and possibly others), and that this race has made contact with a very small number of humans. The majority of the population remains unaware of the aliens' existence, and so this universe's Earth has remained almost indistinguishable to our own.

The Abyss UniverseEdit

In this universe, Earth is very similar to its real-life counterpart. The main difference is that the planet is known to a race known to humans as the N.T.I. (Non-Terrestrial Intelligence). The N.T.I.s dwell in a ship of theirs deep in the Caribbean Sea. After seeing humanity's destructive nature for themselves, they threaten to create megatsunamis that would crash onto every coastline on the planet. They cease this action when convinced of the good humanity is capable of, and they raise their ship out of the ocean. Whether or not the N.T.I.s officially revealed themselves to the human race as a whole is not yet known.

James Cameron's Avatar UniverseEdit

In this universe, Earth is seen in the year 2152, when it bears the scars of centuries of human industry. Its few remaining natural resources are being burned for the high energy demands of its twenty billion strong population. Humans are the only species left not critically endangered or extinct. This situation has not only let to a rapid decline of available methods for generating energy, it has also seen the rise of famine, poverty, terrorism and general worldwide instability. In the face of the rising threat of a global energy crisis, The Resources Development Administration launched an operation to secure the mineral wealth of Pandora. When this failed, the RDA was likely left completely bankrupt. When the planet's resources finally run out, it is very likely that Humanity will not last much longer.

Ocean Girl UniverseEdit

The People of the Ocean refer to Earth by the name Opal Planet. A ship carrying the young princess Neri crash-landed on Earth in the 20th century, where she lived for many years on an uninhabited island off the coast of Australia.

Star Blazers UniverseEdit

In the Kid's Sci-fi anime show Star Blazers, Earth is depicted in the year 2199 CE. An extra-terrestrial species called Gamilons launch hundreds of Planet-Bombs starting in ~2195 CE. They are doing this to raise the level of radiation in the atmosphere, and the humans are forced to move underground, until the star force returns from a alien planet with a machine that can remove radiation.

Chronology of extraterrestrial visits/invasionsEdit

This is a list of contacts with extraterrestrials from various planets from popular culture and fiction.

This section is still incomplete. You can help Alien Species Wiki by adding the information that's missing.

Prehistory Edit

  • Uknown Date: Two creatures who would later be known as mice contracted a race of beings from the planet Magrathea to create a planet which would serve as a highly advanced supercomputer to calculate the Ultimate Question of life, the universe and everything so that the answer could be understood. That planet was built, and named Earth. (Hitchhiker's Guide to the Galaxy)
  • Five billion+ Years ago: An Engineer arrives on Earth and uses its own DNA to seed Earth's oceans with the necessary components to create life. (Prometheus)
  • Four billion years ago:
    • A Salaxalan ship explodes while trying to land on Earth, generating the energy that would allow the formation of the first signs of life upon the primitive world. The ghost of the alien pilot wanders through the Earth for uncounted ages, watching the development of human civilization and eventually attempting to go back in time to fix his error. (Dirk Gently's Holistic Detective Agency)
    • The "ancient humanoid"s seed Earth's oceans with DNA molecules to be incorporated by the primitive lifeforms, eventually resulting in the emergence of the Human race, and prior to that, possibly the Voth race as well. (Star Trek universe)
  • Several alien races have colonized Earth during prehistoric times, including the Elder Things, the Flying Polyps and the Great Race of Yith. (Cthulhu Mythos)
  • During the Mesozoic, Earth was visited by alien creatures assuming the appearance of dinosaurs known as "Rainbow Faces". (The Land Before Time VII: The Stone of Cold Fire)
  • Twenty million+ years ago: a flying saucer of unknown origin crashed into what is now Antarctica. (The Thing)
  • Three million years ago: a sophisticated alien race places a mysterious object with the appearance of a monolith on Earth, which causes the Human race to evolve and achieve sapience. (2001: A Space Odyssey)
  • When Homo erectus ruled the Earth, an ancient and legendary humanoid species known as Anunnaki visited our ancestors, and perhaps influenced their evolution. (popular culture)
  • At some point in prehistoric times, an alien called The Great Gazoo was banished to Earth, where he became friends with some local cavemen. (The Flintstones)
  • About 50,000 years ago: the Protheans, who established a evolutionary research base on Mars, closely studied Cro-Magnon humans in the hopes that they could be consulted in the next extinction cycle to help in the fight against the Reapers. (Mass Effect series)

Ancient History Edit

  • Thousands of years ago: an ancient Antarctican civilization was visited by the Yautja, which were worshiped by the natives and also known to breed Xenomorphs on Earth for hunting purposes. (Alien vs. Predator)
  • 50 BC: a small village in Gaul was visited by two rival alien races, the Tasilweny and the Nagma, both of which were interest in the local druid's magic potion which gives super strength for those who drink it. (Asterix and the Falling Sky)

Medieval Era Edit

  • Dragon eggs arrived on Earth trapped inside meteors. (Dragon Storm)

19th Century Edit

  • 1898: Earth is invaded and nearly conquered by Martians. The aliens were ultimately killed by pathogenic bacteria. (The War of the Worlds)

20th Century Edit

  • 1931: a research group in Antarctica finds the remains of a crashed starship buried into the ice. An old extraterrestrial shapeshifting menace nicknamed The Thing attacks their basement. (Who Goes There?)
  • 1946: an Unidentified Flying Object (U.F.O) crashed to the ground near to Roswell, in Texas. Ufology has officially begun. (popular culture)
  • 1951:
    • A flying saucer crash-lands in the Arctic. A group of scientists recover The Thing inside, which begins terrorizing them until it is finally destroyed by concentrated electricity. (The Thing From Another World)
    • Also the same year, Klaatu arrives in an attempt to encourage humanity to make peace with itself. (The Day the Earth Stood Still)
  • 1956: Earth was invaded by the Pod People. (The Invasion of the Body Snatchers)
  • 1957: a giant intelligent Black Cloud approaches the solar system and establishes contact with Humans. (The Black Cloud)
  • 1958: the Earth is invaded by the Blob, a non-sapient amorphous creature that consumes almost anything on sight. The Blob was frozen and left in the Arctic Ocean, where it probably still remains today. (The Blob)
  • For 15 years during the Cold War, the Hurrians have secretly lived on a colony on the dark side of Luna, waiting for a nuclear war to start on Earth, so that they could take advantage of the situation and have control over Humans. The war never happened, though, and the Hurrians eventually gave up and left. (The Gentle Vultures)
  • In the 1970s, the secret organization of the Men In Black was funded and Earth was classified as a neutral zone, and a safe place for alien refugees from many parts of the galaxy. Since then, several alien species have been secretly living on Earth, including Remoolians, Arquillians and Worm Guys, among countless others. (Men In Black)
  • 1984: a Starman arrived on Earth responding to Voyager II, and befriended a young widow. (Starman)
  • 1996: the Earth is invaded by a race of nomadic aliens who wish to exterminate the human population and consume all natural resources on the planet, then move on to consume another world. A world wide resistance consisting of the remains of the Humans' armed forces commence a counter strike against the invaders to stop them, destroying their entire race. (Independence Day)
  • 1997: astronomer Eleanor Arroway makes the first successful contact with an intelligent and peaceful race from Vega, and through technological plans they transmitted gets to meet a Vegan, although in a simulated environment. (Contact)
  • 1999:
    • Astronaut John Crichton attempts to use Earth's gravity as a source of acceleration, accidentally opening a wormhole and sending him into another part of the galaxy. (Farscape)
    • The creature known as Gonzo finds out that he's not native to Earth at all, but actually an alien and successfully manages to contact and meet with his alien brethren. (Mupppets from Space)
  • In the late 20th century, the Earth was destroyed by the Vogons so that they could build a hyperspace route on its place. It is revealed that the planet was actually a supercomputer built by the Magratheans at the request of Interdimensional Mice in order to seek out the great question to life, the Universe, and everything. A Betelgeusian named Ford Prefect and a Human named Arthur Dent were among the few who escaped the destruction of Earth. It was later built again, but was also destroyed a second time by the Vogons. (The Hitchhiker's Guide to the Galaxy)

21st Century Edit

  • 2003: John Crichton returns to Earth alongside a number of extraterrestrial companions, but leaves to deal with a greater enemy. (Farscape)
  • 2063 April: Vulcans make first contact with Earth after witnessing the launch of the Phoenix. (Star Trek: First Contact)
  • 2089: Scientists Elizabeth Shaw and Charlie Halloway discover a series of cave paintings which seem to suggest humans may have extraterrestrial origins. (Prometheus)

22nd Century Edit

  • c.2100: a form of faster than light travel known as Super-Photonic is discovered by the Earthling Human beings on planet Mars not to be confused with the New Scotlandish or the Arthlings Human beings. (Starflight)
  • 2164: The first large-scale invasion of Earth by the Daleks takes place. (Doctor Who)
  • 2199: Gamilons attack the Earth with radiation-filled Planet Bombs. (Star Blazers)

23rd Century Edit

  • The Decapodians first arrive on Earth at some point of the 23rd century, resulting in the extinction of anchovies. (Futurama)

24th century Edit

  • At this point, several alien species have immigrated to Earth and now live alongside Humans. (Star Trek universe)

Distant Future Edit

  • Billions of years into the future, long after the Galactic Empire has left the galaxy, the biologically immortal creature known as "The Giant Polyp" still resides in a small lake on Earth, where he and his robot companion wait for the arrival of "the great ones". (The City and the Stars)

See alsoEdit

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