Jörðin

Jörðin, also known as Earth, is the third planet from the Sun and the only known astronomical object to harbor life. It is the fifth-largest planet in the Solar System in terms of size and mass. Earth's equatorial diameter is approximately 12,742 kilometers, and its polar diameter is about 12,714 kilometers, resulting in an average radius of 6,371 kilometers. The planet's mass is about 5.97 × 10^24 kilograms.

Earth is primarily composed of iron (32.1%), oxygen (30.1%), silicon (15.1%), and magnesium (13.9%). Its surface is approximately 70.8% water, with the remaining 29.2% being land. The planet's atmosphere is composed of approximately 78% nitrogen, 21% oxygen, and trace amounts of other gases.

Earth's axial tilt is responsible for the changing seasons. The planet's magnetic field, generated by its liquid outer core, protects it from solar wind and cosmic radiation. Earth's only known natural satellite is the Moon, which orbits at an average distance of about 384,400 kilometers.

The planet's biosphere supports a diverse range of life forms, including humans. Earth's climate has been shaped by geological processes such as plate tectonics and the greenhouse effect. The planet's history includes several mass extinctions, with the most recent being the Cretaceous–Paleogene extinction event, which led to the extinction of the non-avian dinosaurs.