This article contains spoilers from the most recent DCEU film. You have been warned.
Earth is a rocky planet orbiting the Sun, and the third planet from the star it orbits. It is the densest and fifth-largest of the eight planets (not counting the one dwarf planet Pluto) in the Solar System in the Milky Way. Earth is notably the home of both humans (the planet's dominant intelligent species) and metahumans (the planet's superpowered minority, which includes Amazons and Atlanteans).
Earth is orbited by the Moon.
The planet Earth is around 4.5 billion years old.
In more recent times humans were created by the Olympian God Zeus, and they ultimately become the dominant species on the planet, and in time, developed their own unique forms of technology and society. They spread their civilization across almost all the inhabitable parts of the planet. Only twice in the history of mankind has the human race been involved in near total global warfare with World War I and World War II respectively.
Some time after their creation, the God of War Ares would strive to malevolently corrupt humanity with war and violence, due to his immense hatred of them, inducing Zeus to create the Amazons, as a means to spread love and mutual understanding among humanity, countering Ares' influence.
Earth's first contact with extraterrestrial beings was in 28,000 BC, during the invasion of Steppenwolf with his Parademon army (on the orders of Darkseid), but the invasion would be fought off by a mighty alliance of Amazon, Atlantean and human armies with some assistance from two members of the Green Lantern Corps , with them driving Steppenwolf from Earth, and dividing his remaining 3 Mother Boxes among themselves, with each of the 3 victorious races receiving one.
Roughly in 3,000 BC, Ares induced humanity to conquer and make slaves of the Amazons, leading to Hippolyta and Antiope valiantly fighting to free their people once more. Meanwhile, the other Olympian Gods expressed their open disgust at Ares' violence and extremist, inducing the God of War to wage the War of the Gods against them, in which he slaughtered all of the other gods, until only Zeus remained. Zeus would defeat, wound, and drive his malevolent son into retreat, but was mortally wounded himself in the process. Before succumbing to his wounds, Zeus would father the "Godkiller" Diana by Hippolyta, and create the protected island of Themyscira for the Amazons to hide from Ares on, in order for humanity to once again have a godly savior from Ares one day.
Earth's second contact with extraterrestrial beings occurred 30 millennia later, in 2013, when Krypton's military leader, General Zod broadcast a message to the people of Earth announcing that they were not alone in the Universe and that he was in search of a member of his race who had been inhabiting their planet for over 33 years posing as a human.
After a separate attack that left Smallville, Kansas in ruin, General Zod attempted to alter Earth's atmosphere and create a new Krypton, partially destroying the city of Metropolis in the process. However his plan was ultimately foiled and Zod himself was defeated and killed by Superman.
Later on, determined to cease Superman's existence, in 2015 Lex Luthor unleashed the devastating abomination Doomsday that could have easily brought about the eventual extinction of human civilization on Earth if left unchecked. Weaponry of the U.S. military proved completely ineffective against the might of Doomsday which included fighter jets and a nuclear warhead. With the ability to unleash massive amounts of destructive energy to heal itself from any attacks, Doomsday proved to be near unkillable and more than even Superman, Batman, and Wonder Woman could handle. Only near perfect coordinated attacks from the trinity, and Superman's willingness to sacrifice himself to kill the Kryptonian/human hybrid monster using a Kryptonite spear (that ultimately weakened them both) saved the day. Though not without cost, as Superman and Doomsday delivered the final deathblows to each other Earth was saved once again, but now more vulnerable than ever with more eventual alien invaders on the way and Earth's most powerful champion presumed dead. These events prompt Batman to work with Wonder Woman to recruit a metahuman response team (the Justice League) to fill the void left by Superman's death, as Earth is almost certain to have another huge confrontation with powerful threats on the horizon.
When the ancient metahumans, Enchantress, and her brother, Incubus threatened to take over the world, the director of ARGUS, Amanda Waller sent Task Force X into the field to defeat them. Task Force X, a team of incarcerated criminals with exceptional abilities and skills, which could be forced to battle against such formidable threats, successfully defeated the powerful metahumans and saved the world.
In the present Steppenwolf sensing that earths defenses were lowered with the death of Superman enacted his second invasion of Earth. However he was once again defeated by the newly formed teamed of heroes known as the Justice League which consisted of a revived Superman.