Home to millions of species including humans, Earth is currently the only place where life is known to exist. The planet formed 4.54 billion years ago, and life appeared on its surface within a billion years. Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land. The physical properties of the Earth, as well as its geological
history and orbit, have allowed life to persist during this period. The
planet is expected to continue supporting life for at least another 500 million years.