Facts for Kids

Ocean means the huge bodies of salty water that cover about 71% of Earth. The open water is very deep in many places — often more than 3,000 meters — and the total ocean area is about 361 million square kilometers. Seawater is salty because it holds dissolved minerals; on average the salt is about 3.5% of the water, and in most places it ranges from about 30 to 38 parts per thousand.

Scientists think of all the seas and named oceans as one connected World Ocean. Currents and waves move water and heat around, so the oceans help control weather, give homes to many sea animals, and link countries across the globe.

Nature is everything that exists in the world and the universe: living things like trees and animals, and non-living things like rocks, weather, and sunlight. It includes the rules that make plants grow, rivers flow, and stars move. People are part of nature, too, even though sometimes people act as if they are separate from it. Because humans can change the land and make cities, ideas about nature have changed over time. Long ago, many thought nature stayed the same, but scientists learned it can change and bring new kinds of life and places.

Earth formed a very long time ago, when dust and gas around the young Sun clumped together to make planets. This happened about 4.5 billion years ago. Not long afterward, another large piece joined up and formed the Moon. As the new planet cooled, its outer layer hardened into a crust and volcanoes and gases made a first air around the world.

Water vapor in that air turned to rain and filled low places to make the first oceans, and some water may have arrived on icy comets. Very early, about 4 billion years ago, the first simple molecules that could copy themselves appeared — the start of life.

River is a moving ribbon of freshwater that flows from higher places toward a larger body of water, like a lake, the sea, or another river. Rivers usually begin at a source—sometimes a spring or melting snow—then wind along as streams join them, and finally reach a mouth where they spill into something bigger. Some rivers dry up or sink into the ground before they reach the sea.

Rivers are part of the water cycle: they carry rain and melted snow downhill, shape the land by carving valleys, and give homes to plants and animals. People use rivers for drinking water, farms, travel, and gentle power, so keeping rivers clean helps nature and people.

Microbes are living things so small you need a microscope to see them. The first life on Earth was made of single tiny cells like microbes, and they began a very long time ago—billions of years. Microbes could copy themselves and pass traits to new generations. Over time, small changes and natural selection led to many sorts of life.

Some early microbes used sunlight to make food and put oxygen into the air. That oxygen helped make a protective layer high above Earth so plants and animals could live on land. Later, tiny cells joined together inside other cells, and this helped create the larger, more complex cells that make up most plants and animals.

People make up only a tiny part of the Earth’s living weight, but we have a very large effect on the planet. The word biomass means the total weight of all living things. Because people build cities, grow food, and move things around, our actions can change whole forests, rivers, and seas—even far from where we live.

The line between “natural” places and human-made places is often blurry. Scientists use the term anthropogenic mass to mean all the stuff people have made, like buildings, roads, and plastic. That man-made mass now weighs more than all the living things on Earth, and plastic alone is heavier than all land and sea animals combined.

Places with little or no human influence are shrinking. Only about 3% of the land still has healthy, original groups of plants and animals living there. A growing human economy and more land used for cities or farms can push other species out by changing or taking their homes. Small choices, like using less plastic and protecting wild places, can help nature stay healthier.

Atmosphere means the thin blanket of gases that surrounds our planet and stays close because of gravity. It is mostly nitrogen and oxygen, with some water vapor and tiny amounts of other gases. Higher up the air gets thinner and colder. The ozone layer in the upper air helps protect life by blocking harmful rays from the Sun and helps nights stay warmer.

Weather happens in the lower part of the atmosphere and can change quickly — that is why we can only forecast it well for a few days. Seasons come from Earth’s tilt and make different parts of the world warmer or colder. Climate is the long-term pattern of weather in a place and depends on things like ocean currents, how much sunlight an area reflects, greenhouse gases, and slow changes in Earth’s path around the Sun.

Wilderness means places that are mostly left alone by people—forests, mountains, deserts, and even quiet river edges in towns. Biodiversity is the big mix of different kinds of plants, animals, and other life that live there. Together, wild places and biodiversity make homes for many species and keep nature balanced.

Protected parks and preserves help species survive and give scientists places to learn. Wilderness areas keep old genes and plant types that are hard to copy in zoos or gardens. For many people, wild places also bring calm, inspiration, and a reminder that Earth cares for itself in many clever ways.

Plants and animals are two familiar groups of living things. Plants usually make their own food from sunlight, while animals eat plants or other animals. Long ago, people grouped life simply into plants and animals, but scientists later found more groups, like fungi and tiny algae.

All living things change gradually over many generations through evolution, which is how species become better suited to their homes or sometimes disappear if they cannot adapt. Some animals are wild, some are kept by people as pets or farm animals, and others live in labs. These categories show how humans and nature connect.