Earth

} is the third planet from the sun and is the only known planet that supports life. It has a diameter of approximately 12,742 kilometers and a mass of 5.97 x 10^24 kg. It has an atmosphere consisting of 78% nitrogen, 21% oxygen, and 1% other gases, which helps to regulate the planet's temperature and protect it from harmful solar radiation. The planet has one natural satellite, the Moon, which is the fifth-largest satellite in the solar system.

Biology
Earth is home to a vast array of life, from microscopic bacteria to large mammals. The diversity of life on Earth is a result of evolution, the process by which species change over time through natural selection. Life on Earth is supported by the planet's biosphere, which is the thin layer of living organisms that exist on and near the planet's surface. The biosphere is supported by the planet's ecosystems, which are complex communities of organisms and their physical environment.

History
Earth is estimated to be around 4.54 billion years old, and its history is divided into different geological eras, each characterized by distinct geological, biological, and environmental events. The earliest era is the Hadean, which began with the formation of the planet and ended around 4 billion years ago. During this time, the planet was bombarded by asteroids and comets, and volcanic activity was widespread.

The next era was the Archean, which lasted from 4 billion to 2.5 billion years ago. During this time, the first life forms appeared on Earth, and the planet's atmosphere began to take on its modern composition. The Proterozoic era followed the Archean and lasted from 2.5 billion to 542 million years ago. During this time, the first multicellular organisms appeared, and the first animals evolved.

The most recent era is the Phanerozoic, which began around 542 million years ago and is still ongoing. This era is characterized by the diversification of life, including the evolution of plants, animals, and fungi. It is also marked by several mass extinction events, including the one that killed off the dinosaurs around 66 million years ago. Today, Earth continues to evolve, with humans exerting a significant impact on the planet's environment and ecosystems.