Earth

Earth is the home planet of Humans and various animals. It consists of seven continents. It is home to a wide array of different creatures. Earth's history goes back as far as about 4.6 billion years ago when the planet first formed, with the first single celled organisms appeared about 3.5 billion years ago. These simple organisms eventually began to evolve into more and more advanced creatures. A certain species of exceptional intelligence, humans or Homo Sapiens, evolved about 200,000 years ago. They eventually began to show signs of sentience and made it into space in 1961. Several centuries after they became a spacefaring race, humans encountered a collective of intelligent, hostile extraterrestrials known as the Covenant. Thus begins the story of Halo.

Discovery of Earth
The Covenant originally had no knowledge about humanity's home world, mostly thanks to the development of the Cole Protocol. Sometime between the events of Halo and Halo 2, the Covenant eventually discovered Earth's location. The Prophet of Regret led a small expeditionary force consisting of 15 ships(2 assault carriers in the fleet), but was surprised to find that humans had inhabited the planet. At the end of Halo 2, the Covenant had eventually begun a full-scale invasion of Earth, and have completely overrun Africa by the beginning of Halo 3.

Many theories about Earth erupted when the Halo 3 Announcement Trailer was shown.

The Covenant had discovered a massive Forerunner structure several miles wide buried under the ground where the city of New Mombasa used to be. Is this the Ark? If so, why was it on Earth?

The Prophet of Regret had obviously come to Earth in search of a Forerunner artifact that might determine the fate of all sentient life in the galaxy, as the massive firepower that the Halos yield could destroy all life "with sufficient biomass to sustain the Flood" "within 3 radii of the galactic center," as stated by 343 Guilty Spark in the games.

Africa is the most important place on Earth in regards to the Halo story, it seems, and, coincidentally, it is theorized to be the birthplace of humanity.

It is revealed through the storyline of the first two games that the Forerunners have some sort of connection to humanity.

Thus, the power of the Covenant was not fully dedicated into glassing Earth. Though the Covenant Fleet consisted capital ships, flagships and such, several of the Covenant Fleet were hanging around in the outer regions of the Milky Way Galaxy. In fact, many of the Covenant Fleet were still at Reach and others were dedicated in finding more Halos. Moreover, given that Cario Station and its planetside power generator are still intact at the end of Halo 2, it may be assumed that the UNSC is having some success, however small, with at least holding the Covenant forces at bay. The conclusion of the Second and the ultimate fate of Earth herself wait to be revealed in Halo 3

Planetside
Africa
 * Republic of Kenya
 * Mombasa
 * New Mombasa
 * New Mombasa Orbital Elevator
 * Old Mombasa
 * Voi
 * Diego Garcia - Island in the Indian Ocean
 * United Republic of Tanzania
 * Zanzibar Island

Oceania
 * Commonwealth of Australia
 * Sydney, Australia
 * HighCom Facility Bravo-6
 * Sydney Synthetic Intellect Institute

Asia
 * Korea
 * Kyonggi Province
 * Songnam
 * Special Warfare Center

North America
 * United States of America
 * Boston, Massachusetts
 * Chawla Base
 * Chicago, Illinois
 * Tactical Autonomous Robotic Defence System
 * Mexico
 * Base Segundo Terra - Mexico City, Mexico
 * Cuba
 * Havana
 * Centennial Orbital Elevator

Europe
 * Federal Republic of Germany
 * Essen
 * Beweglichrüstungsysteme Testing Facility

Orbital

 * Athens Station
 * Cairo Station
 * Malta Station
 * Nassau Station
 * Onan Station
 * Station Wayward Rest

Luna
 * Luna OCS Academy