{{Location Infobox
|location=WikipediaSolar System|Solar System
|affiliation= *Human race

'''Earth''' is the third planet in the Sol planetary system, most notably inhabited by humans, and orbited by the Moon. After the Black Mesa Incident, the planet became overrun by hostile alien creatures from the Xen borderworld, and later taken over completely by the Combine.


Shortly after the development of teleportation technology at Black Mesa, the Xen borderworld was discovered. Scientists began investigating Xen and experimenting on the creatures found there by traveling through portals to reach it. 

Experiments into mysterious Xen crystal|crystals found on the borderworld led to a catastrophic event, dubbed the Black Mesa Incident, which tore open the gateways between the dimensions and allowed waves of aliens to spontaneously travel through and begin attacking the unprepared scientists. This resonance cascade caught the attention of the Combine|Combine empire, who, after the detainment of Gordon Freeman and the destruction of the Black Mesa Research Facility began to send their own legions to Earth. A short but decisive battle between the world's military and the Combine ensued, later called the Seven Hour War, ultimately resulting in the enslavement of Earth's human population.

Under Combine control, Earth was left in utter chaos. The Combine began to strip the Earth of any useful natural resources, the planet being "picked to the bone". The most noticeable sign of this was the considerable drop in sea levels as water was drained and brought to other Combine worlds. Toxic and radioactive waste is prevalent in many areas, making them inhospitable. 

Deleted material from the game included a Combine airship 'absorbing' the air while distributing a collection of chemicals that are harmful to humans into the atmosphere. Also, the introduction of fierce, extraterrestrial lifeforms such as the Antlions and headcrabs left possibly all of Earth's natural lifeforms either extinct or critically endangered. Because of all of these factors, even if the Combine rule ends, extensive rebuilding, cleanup, and Xeno-extermination would have to take place to make the planet habitable again.

The originally hostile Vortigaunts united with the humans and became part of the Resistance, an underground alliance who intended to overthrow the Combine and regain control of the planet. Bases were set up and over several years they gained much information on the Combine. The reappearance of Gordon Freeman led a sudden spur of movement and attacks from the Resistance, called The Uprising, allowing them to usurp control from the Combine forces in and surrounding City 17, destroying the Citadel Core and irradiating the entire surrounding area after escaping to bases in The Wasteland. 

City 17's Core destruction broke down the Combine's lines of communication, leaving them stranded within their settlements on Earth. In an attempt to bring more forces through and thwart the Resistance, the Combine induced the Citadel's destruction, causing it to produce a Superportal. At White Forest, the Resistance were able to launch a rocket into space to take advantage of a satellite network to close the Superportal before it matured and fully opened. 

The Resistance has so far been successful in remaining covert and outside of the Combine's control, however as yet the outcome of their endeavors is unknown.

However, at the end of ''Portal 2'', it remains unclear if the Combine have won the battle. Chell emerges in a sunny wheat field, and the sky is blue and healthy-looking, unlike the polluted, dark sky the Combine take care to cultivate, and the presence of the crops seem to indicate that the Combine have failed in draining Earth's resources. 

However, these elements might have just been used to enhance the idea that Chell is finally free and leaving Aperture Science. Alternatively, they may indicate that the Combine has moved the vast majority of humanity elsewhere (such as Europe) and has since concentrated its efforts there, largely ignoring North America. Although before the end of ''Portal 2'' Chell goes through a portal onto the Moon as part of the final boss battle between her and Wheatley, and briefly looks at the Earth which appears to be healthy.

==Notable locations==

===Black Mesa Research Facility===
{{main|Black Mesa Research Facility}}

The '''Black Mesa Research Facility''' was an underground research installation located in the wikipediaNew Mexico|New Mexico desert. Notable for its scientific developments, such as portal technology and advanced weaponry, it was the epicenter of the Xen invasion. The research facility was later destroyed by the military in an attempt to control the alien infestation.

===City 17===
{{main|City 17}}

'''City 17''' was one of many major Combine-installed cities on Earth, located in an unnamed European city and the base of administration of Wallace Breen|Dr. Wallace Breen, the puppet administrator of Earth appointed by the Combine.

Located in Eastern Europe, the city boasts characteristic architecture, though most of it has been either outfitted with Combine technology or destroyed altogether. The Combine Citadel, located at the center of the city, was the headquarters of the Combine empire on Earth as well as Dr. Breen's office. It also provided all of City 17's electricity via a Dark Energy generator, which was later destroyed by Gordon Freeman in an attempt to prevent the creation of a Superportal to the Combine homeworld.

===Aperture Laboratories===
{{main|Aperture Laboratories}}

'''Aperture Laboratories''' are the head-quarters of Aperture Science, another research organization hired by the US government at first to manufacture shower curtains. Located in a Salt Mine (bought by Cave Johnson, Founder of Aperture Laboratories) in The Upper peninsula of Michigan, the main building consists of an underground Enrichment Center, which is monitored and controlled by a powerful AI, GLaDOS. Preceding the death of their Cave Johnson|founder, the company started developing portal technology, most notably the Aperture Science Handheld Portal Device. The building was famously locked down by GLaDOS with employees still trapped inside. GLaDOS was later partially destroyed by a surviving Chell|test subject, but remains "alive".

Sometime before the Black Mesa Incident, Aperture Laboratories had a research vessel named the ''Borealis'', which was rumored to contain a top-secret project, but lacked several critical safety features due to lack of funds. It has gained legendary status ever since the entire ship, along with a large portion of its dry dock, mysteriously vanished one night, never to be heard from again until it was found many years later by Judith Mossman, deep within a frozen crevice in the wikipediaArctic Circle|Arctic Circle.

===White Forest===

{{main|White Forest}}

'''White Forest''' is an alpine missile base that was abandoned after the Cold War, and later purchased by Black Mesa in response to budgetary issues. The human Resistance later took over the site as a major base of operations, and use one of its rockets to stop a Superportal from opening up and preventing a massive Combine invasion.

After the Black Mesa Incident, the few remaining scientists escaped to White Forest in an effort to protect themselves. Secure from the Combine tyranny and surrounding alien hazards, it is a haven for many survivors and resistance fighters.

==List of appearances==
{{Imagecat|Earth images}}

*''Half-Life Day One'' {{1st}}
*''Half-Life Uplink'' {{Nc}}
*''Half-Life Opposing Force''
*''Half-Life Blue Shift''
*''Half-Life Decay''
*''Half-Life 2''
*''Half-Life 2 Raising the Bar''
*''Half-Life 2 Lost Coast'' {{Nc}}
*''Half-Life 2 Episode One''
*''Half-Life 2 Episode Two''
*''Portal First Slice''
*''Portal ARG''
*''Portal 2''

==See also==
*Earth creatures