Earth is the third planet from the Sun and is the largest of the terrestrial planets in the Solar System, in both diameter and mass. It is home to a myriad of species including humans. It is the only planet in the universe known to support complex life.
Most Harry Turtledove works, particularly the alternate histories, are set on Earth, although this fact is rarely "vital" to the action of the story. Several science fiction stories feature Earthlings colonizing other planets or contact with alien races.
Many events from Earth's geological past were popular fodder for time-viewer recordings. However, few people thought to look forward with the time-viewer, and so were completely surprised when a comet hit the planet.
Around 25,000 BC, aliens from the Foitani Empire visited Earth. The Foitani were a race that methodically practiced genocide upon lesser advanced peoples who were in their way. Operating in this mindset, they determined that primitive humans might evolve into a dangerous rival to them. As such, they invented a plague weapon which failed to eradicate humanity, instead becoming known as the common cold. The Foitani also collected biological specimens from Earth, including a primitive man and woman.
Shortly after the failure of their plan of Terran genocide, the Foitani Empire self-destructed from the Suicide Wars. In the meantime, humans spread beyond the limits of Earth to colonize various planets including Saugus, becoming the technological equals of what remained of Foitani civilization.
In 2039, a Roxolan invasion fleet arrived in the Earth's solar system. It was first detected by the crew of the Ares III, the third manned mission to Mars. The crew attempted to communicate but their radio signals were ignored and the Roxolan fleet proceeded to Earth since they had not detected any signs of hyperdrive. All vessels landed and deployed their foot-soldiers to horrible effect.
Earth was the galaxy's least important planet but also its sleazy-media center. For this reason, anything that happened there received more attention than it deserved. Thus, when the baroque throne room and somewhat-less-baroque antechamber were stolen from Versailles, in a second-rate country on a third-rate continent with a glorious future behind it, the rash of throne room thefts came to the galaxy's attention. The Space Patrol sent Cadet Rufus Q Shupilluliumash to examine the crime scene.
While inspecting a man's solar system, a salesman named Eric found that wanderer three had gone moldy. He added that it would need steam cleaning but said that there wouldn't be any extra charge. Eric added that the crew would arrive between nine and eleven the next morning and while it would be a little noisy, it wouldn't be too bad.
The Earth and its Moon were visible from the planet Minerva. The Minervans called this collective body the Twinstar. A few Minervans who encountered humans correctly guessed the Twinstar as the new creatures' point of origin, but did not ask for confirmation.
A family of intergalactic travelers visited Earth in the Cambrian age, when very primitive plant and animal life lived exclusively in the oceans. The children's aquarium broke down, and their father reluctantly agreed to let them empty the tank into the ocean.
These new creatures thrived, eventually generating the diverse creatures of planet Earth.
The Race referred to the Earth as Tosev 3. They tried and failed to conquer the planet in the 1940s, which was already embroiled in a global conflict. While the Southern Hemisphere of the planet did fall rather rapidly, the Northern Hemisphere was able to fight the Race off and retain their autonomy.
For the next two decades, humans and the Race maintained a cold war, while both sides saw a substantial cross-pollination of cultures. Leaders of the Race frequently considered instigating a nuclear war with the dominant local powers to render the planet uninhabitable and destroy these influences, but before they made this decision the "Tosevites" had eclipsed them technologically, making this impossible.
The Race introduced certain of their domestic animals and plants to Earth, with many arriving with the Colonization Fleet in 1962. These new arrivals played havoc with Earth's ecology, even in areas not under the Race's control.