Earth Science

What earth science studies

Earth science is the study of the planet: its rocks, its oceans, its air, and how they change over time. The Earth is about 4.6 billion years old.

Inside the Earth

The Earth is built in layers. The crust is the thin, rocky outer layer we live on. Below it is the mantle, a thick layer of hot rock that moves very slowly. At the center is the core, mostly iron and nickel, and extremely hot.

Moving plates

The crust and the top of the mantle are broken into huge pieces called tectonic plates. The plates move a few centimeters a year, about as fast as your fingernails grow, and they carry the continents with them.

Most earthquakes, volcanoes, and mountain ranges are found where plates meet. Where two plates slide past each other, they catch and then slip, and the ground shakes: an earthquake. Where one plate sinks beneath another, rock melts and can rise to the surface in a volcano. Where two plates push together, the crust crumples upward into mountains. That is why earthquakes and volcanoes cluster along the same lines on a map, such as the ring around the Pacific Ocean.

Reading rock layers

Many kinds of rock form in layers, one on top of another. In layers that have not been disturbed, the bottom layer is the oldest and the top layer is the youngest. Fossils, the preserved remains or traces of living things, are found inside the layers. So rock layers work like a record of the past: the deeper the layer, the further back in time.

Rock is also slowly recycled. Heat and pressure, melting and cooling, and weathering and erosion turn one kind of rock into another over millions of years. This is the rock cycle.

The water cycle

The Earth’s water moves in a cycle driven by the Sun. Heat from the Sun turns water from oceans, lakes, and plants into vapor: evaporation. As the vapor rises, it cools and forms clouds: condensation. The water falls back as rain or snow: precipitation. It runs into rivers, soaks into the ground, and returns to the sea, and the cycle begins again.

Weather and climate

The test often asks you to tell these two apart. Weather is the condition of the air in one place over a short time: today’s temperature, rain, and wind. Climate is the usual pattern of weather in a place over a long time, usually measured over about thirty years. One cold week does not change a climate. Only a long record can show whether a climate is changing.

Resources and hazards

The Earth supplies the materials people live on. Renewable resources, such as sunlight, wind, water, and forests, can be replaced in a human lifetime. Nonrenewable resources, such as coal, oil, and natural gas, took millions of years to form from the remains of ancient living things, so once they are used up they cannot be replaced on any human time scale.

The Earth also brings natural hazards: floods, earthquakes, hurricanes, droughts, and volcanic eruptions. Many happen in predictable places. Rivers flood the low land beside them, earthquakes strike along faults where plates meet, and hurricanes hit warm coasts. Knowing where hazards are likely helps people plan where and how to build.