Earth
Those who dwell among the beauties and mysteries of the Earth are never alone or weary of life. ~ American marine biologist Rachel Carson
Life may have found a precarious hold on a few orbs in the solar system. Venus might have once supported life. Mars almost certainly did and may still.
Mars once had regular wet seasons, rivers, and lakes. Even now there are discharges of methane from the surface of Mars into the atmosphere. This may be from serpentinization: a geological process of rock oxidation and hydrolysis via heat and water. Or it may be microbial methanogens.
Europa is another candidate for life. Even nominally hellish Mercury may harbor microbes, nestled in lakes which never see the Sun.
Earth was something special. Its ability to hold an atmosphere made a difference.
4.55 BYA, Earth came into being by accretion: currents of particles swirling around the Sun collided and coalesced, as with other planets. Molten iron sank to the center, forming the planetary core.
Earth’s continued formation was by violence for at least 800 million years, pilloried by 2018 tonnes of cosmic debris. Enormous impacts occurred as recently as 1.8 BYA.
Impacting meteorites were stirred into Earth’s mantle by massive convection processes. The vast bulk of the planet’s precious metals, including gold, came from space after its formation.
The bombardment continues to this day, but it has been reduced to a fine drizzle. Over 3,600 tonnes of extraterrestrial dust a year – 9 tonnes a day – settle on Earth’s surface.
By 4.4 BYA a crust had formed. A 100 million years later vast oceans covered the surface. Life made its debut on Earth ~4.1 BYA.
