Earth

Earth is the third planet from the Sun. It is the only planet we know has life on it. Earth has huge oceans that cover most of the planet. These oceans have liquid water, which all living things need. About seven out of every ten parts of Earth is water. The other three parts are land where plants and animals live. Most of Earth's land has plants growing on it. At the very top and bottom of Earth are huge sheets of ice and snow.

Earth has a hard outer shell made of giant pieces called plates. These plates move very slowly and bump into each other. When they do, they make mountains, volcanoes, and earthquakes. Deep inside Earth is hot melted rock that creates a shield around our planet. This shield protects us from dangerous rays that come from the Sun. Without this shield, life could not survive on Earth.

Earth has an invisible blanket of air around it called the atmosphere. This air is made mostly of two gases called nitrogen and oxygen. The air also has water vapor that makes clouds. Some gases in the air trap heat from the Sun like a blanket. This keeps Earth warm enough for water to stay liquid. Without this blanket, Earth would be too cold for life. The Sun heats different parts of Earth differently, which makes winds and ocean currents move around the planet. This creates all our different types of weather and climates.

Earth is shaped like a ball and takes about 365 days to go around the Sun. It spins like a top and completes one spin in about 24 hours. Earth is tilted as it spins, and this tilt is why we have seasons. The Moon orbits around Earth and is about one quarter as wide as our planet. The Moon's gravity helps keep Earth stable and creates our ocean tides. Earth formed about 4.5 billion years ago from dust and gas. Life started in the oceans about a billion years ago and slowly spread everywhere. Humans have lived on Earth for about 300,000 years and now live on every continent. Today, humans are changing Earth's climate and hurting many plants and animals, which is a big problem we need to fix.