Earth Systems

Groundwater fills spaces between rocks and soil underground. Aquifers are underground layers of rock that hold and transmit water. Many communities depend on wells that tap into aquifers.

Earthquakes happen when stress builds up along faults in Earth's crust and suddenly releases. Seismic waves radiate from the focus, shaking the ground.

Volcanoes form where magma from the mantle reaches Earth's surface. Shield volcanoes have gentle slopes with flowing lava, while composite volcanoes are steep with explosive eruptions.

Soil forms slowly from weathered rock mixed with decomposed organic matter. Different layers (horizons) form with topsoil on top, subsoil below, and bedrock at the bottom.

Natural resources include materials from Earth that people use. Renewable resources (trees, solar energy) can be replenished. Nonrenewable resources (coal, oil) are limited.

River systems shape the land over time. Young rivers have steep, V-shaped valleys. Mature rivers meander across floodplains. Old rivers have wide, flat valleys and deltas.

Hurricanes form over warm ocean water when moisture and heat create powerful rotating storms. They bring strong winds, heavy rain, and storm surges to coastal areas.

Glaciers are massive bodies of ice that form from compacted snow. They shape landscapes by carving valleys, depositing sediment, and creating features like moraines and cirques.

Landslides occur when slopes become unstable due to heavy rain, earthquakes, or human activity. Gravity pulls loose rock and soil downhill, sometimes with devastating speed.

Tides are the daily rise and fall of ocean water caused mainly by the Moon's gravity pulling on Earth. Most coasts experience two high tides and two low tides each day as Earth rotates.

Deposition is the process of dropping eroded rock and soil in a new location. When wind, water, or ice slows down, it releases its sediment, gradually building landforms like deltas, sandbars, and beaches.

Weather is what the sky is doing today; climate is the pattern of weather over thirty years or more. A cold week says nothing about climate, in the same way one tall pupil says nothing about the average height of a school.

Lines joining places of equal pressure are isobars. Where they crowd together the wind is strong; where they are far apart it is calm. Low pressure usually brings cloud and rain, high pressure settled weather.

Getting metal out of the ground moves enormous quantities of rock, uses a great deal of water and energy, and leaves waste behind. Recycling aluminium uses about a twentieth of the energy of making it from ore.

It takes centuries to build a few centimetres of topsoil and a single storm to strip it from a bare field. Ploughing along contours, planting cover crops and keeping hedges all slow the loss.