Short answers, pulled from the story.
Liquid water covers 70.8% of Earth's surface, creating a hydrosphere that acts as a massive heat reservoir and a cradle for complex organic molecules. The remaining 29.2% of the surface consists of land distributed across four continental landmasses. If all the crustal surface were flattened to the level of a smooth sphere, the resulting ocean would be 2.7 kilometers deep.
A liquid outer core generates a magnetosphere that extends far into space to act as an invisible shield against the solar wind. This magnetic field deflects charged particles that would otherwise strip away the atmosphere and expose the surface to lethal levels of cosmic radiation and UV light. The field also traps high-energy particles in the Van Allen radiation belts to create a zone of safety for life on the surface.
The Moon formed from the collision of a Mars-sized protoplanet named Theia with the early Earth during the giant-impact hypothesis. This collision ejected material that accreted to form the Moon, explaining its relative lack of iron and its composition, which is nearly identical to Earth's crust. The Moon currently orbits the planet at a distance of about 384,400 kilometers.
Oxygenic photosynthesis evolved approximately 2.4 billion years ago during the Great Oxidation Event to transform the atmosphere from a reducing state to an oxidizing one. This event allowed for the proliferation of aerobic organisms and created the ozone layer which blocks ultraviolet solar radiation. The atmosphere is composed primarily of nitrogen and oxygen with trace amounts of carbon dioxide and water vapor.
There are 205 sovereign states existing today with the majority of the human population living in urban areas. Approximately 90% of the eight billion people living in the 2020s inhabit the Northern Hemisphere. The United Nations extends human governance over the ocean and Antarctica to acknowledge the interconnectedness of Earth's environments.
Earth's mean temperature may reach 100 degrees Celsius within 1.6 to 3 billion years, causing all ocean water to evaporate and be lost to space. This runaway greenhouse effect will occur long before the Sun reaches its red giant phase and expands to roughly 250 times its present radius. The Sun will increase in luminosity by 10% over the next billion years and by 40% over the next 5 billion years.