The requirements for life to exist include proper chemistry, the home planet being in orbit in a star's habitable zone and having a large planet in the solar system that attracts asteroids to itself. Another requirement is plate tectonics that control carbon dioxide levels by recycling the crust.
Scientists believe life became possible on Earth because of the presence of carbon and water. Carbon forms varieties of bonds that are the basis for the complex molecules necessary for life. Water's high heat capacity moderates Earth's climate, making it inhabitable. Water also has many properties that make it suitable for acting as the basis of life.
The habitable zone is the distance from a star, in Earth's case the sun, where water can form on a planet and remain in liquid state. Stars also must be the right size. If a star is too large, it likely dies too soon for life to evolve.
The concept of solar system clean-up is when a very large planet attracts asteroids, meteors, comets and other large, dangerous objects to itself so they don't hurtle into the habitable planet or moon, causing a life-destroying catastrophe. In Earth's solar system, the large planet is Jupiter.
Plate tectonics release carbon dioxide locked in the crust into the atmosphere when Earth becomes too cold. The extra CO2 traps solar radiation inside the atmosphere, allowing the air to re-warm. Plates moving around and releasing carbon have warmed Earth several times.
