Our World: Just Right for Life
Remember the story of Goldilocks and the three bears? Goldilocks tried each bowl of porridge. One was too hot. One was too cold. Finally, she found the one that was just right.
Luckily for us, conditions for life on Earth are just right. Earth is the third planet in our solar system. It is 93 million miles (149 million km) from the sun. If it were closer, Earth would be too hot for life to survive. If it were much farther away, it would be way too cold.
Water also makes Earth just right for life. Liquid water lets molecules easily come into contact. This helps chemical reactions needed for life.
Water also makes up an important part of living things. About 90 percent of your own body is water.
Earth also has the right atmosphere for life. As nature writer Rachel Carson put it, we live in an “ocean of air.” It ranges from the Earth's surface upwards toward space.
By volume, air is about 77 percent nitrogen and 21 percent oxygen. We and many other animals need oxygen to breathe. Other chemicals in the air are argon, carbon dioxide, hydrogen, neon, helium, krypton, and xenon. Water vapor — evaporated water — is also in the air.
The atmosphere acts like a blanket. It captures just enough of the sun's warmth and holds it in. Without the atmosphere, Earth's sunny side would be way too hot, and its dark side would be bitterly cold.
The atmosphere is also a sunscreen. Its ozone layer screens out many of the sun's harmful ultraviolet rays.
Our distance from the sun and the presence of water and atmosphere are all just right on Earth. They help life thrive on our planet.