Final answer:
Earth's temperature is maintained by the greenhouse effect, where gases like carbon dioxide and water vapor trap the sun's heat in the atmosphere. This results in a stable climate necessary for life. Earth's unique distance from the sun and hydrosphere also contribute to the planet being habitable.
Step-by-step explanation:
Earth's temperature is regulated by a delicate balance involving the sun's energy and the greenhouse effect. Certain gases in the atmosphere, such as water vapor and carbon dioxide, are critical for maintaining Earth's surface temperatures conducive to life, with an average of around 15°C. If these gases were absent, the earth's average temperature would plummet to -18°C, rendering it inhospitable to life as we know it.
The greenhouse gases absorb heat energy and reradiate it back towards the surface, preventing all the solar energy received from simply bouncing back into space. Additionally, as the Sun has grown more luminous over billions of years, a corresponding decrease in atmospheric carbon dioxide due to weathering has resulted in a stable climate, which has been crucial for the development of complex life forms.
Furthermore, Earth's water bodies, collectively forming the hydrosphere, play an instrumental role in supporting life, contributing to maintaining the planet's overall temperature balance.