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. In OTL, it is the only planet in the universe known to support life.
Most 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, devastating it.
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 is the least important planet in the galaxy but is the sleazy-media center of the galaxy. Anything that happens there receives more attention than it deserves because it happens there. Thus, when the baroque throneroom (and somewhat less baroque antechamber) was stolen from Versailles, in France, a second-rate country on a third-rate continent with a glorious future behind it, it was this crime that brought the rash of throneroom thefts to the galaxy's attention. Space Patrol sent one of their cadets, Rufus Q Shupilluliumash, to solve this crime.
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 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.
A family of intergalactic travelers visted 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.