Weathering

Weathering is the way rocks, soils, and minerals slowly break down and change over time. This happens when they touch water, air, sunlight, and living things. Unlike erosion, which carries these materials away, weathering happens right where the rocks are, without much movement.

A natural arch produced by erosion of differentially weathered rock in Jebel Kharaz (Jordan)

There are two main types of weathering: physical and chemical. Physical weathering breaks rocks apart by things like temperature changes, freezing and melting ice, and wind. Chemical weathering changes the rocks through reactions with water, air, and chemicals from living things. Water is important for both types, but air and the work of plants and animals also help.

When rocks weather away, they mix with organic material to make soil. Weathering, along with erosion and the movement of materials, helps shape many of Earth’s landforms. It is an important part of the rock cycle, and sedimentary rock—formed from weathered material—covers much of Earth’s continents and ocean floor.

Physical

A rock in Abisko, Sweden, fractured along existing joints possibly by frost weathering or thermal stress

Physical weathering breaks rocks into smaller pieces without changing what they are made of. This happens mostly when temperatures change a lot. For example, when water inside cracks in rocks freezes, it gets bigger and pushes the cracks wider. This is called frost weathering and is a common way rocks break apart.

Rocks can also break apart when they heat up during the day and cool down at night. This constant changing can cause the rock to split into pieces. This process is important in places with big temperature changes, like deserts. Rocks can also break apart when pressure from deep underground is released. Living things like plants and lichens can help break rocks apart by growing in cracks and pushing them open.

Chemical

Comparison of unweathered (left) and weathered (right) limestone

Most rocks form deep underground where it is hot and squeezed tightly together. When they come close to the surface, they meet cooler, wetter air and rain. This changes the rocks very slowly.

Water, oxygen, and carbon dioxide in the air and rain mix with the rocks. They change the rocks and break them apart. This is called chemical weathering.

Water is the biggest helper in chemical weathering. It changes many minerals into clay or other things. Oxygen also helps by changing some minerals. Carbon dioxide mixes with water to make a weak acid. This weak acid can melt some rocks, like limestone. Tiny living things, like plants and small organisms in the soil, can also help this process by giving out acids and gases.


Bond	Relative strength
Si–O	2.4
Ti–O	1.8
Al–O	1.65
Fe⁺³–O	1.4
Mg–O	0.9
Fe⁺²–O	0.85
Mn–O	0.8
Ca–O	0.7
Na–O	0.35
K–O	0.25

Ocean floor

Weathering of the ocean floor happens differently than weathering on land. It is a slow process. Basalt rock becomes less dense over time. About 15% of the basalt changes every 100 million years. During this time, the basalt absorbs water and gains more iron, magnesium, and sodium, while losing some other minerals like silica and calcium.

Buildings

Concrete damaged by acid rain

Buildings made of stone, brick, or concrete can break down because of weather, just like rocks can. Statues, monuments, and decorative stonework can also be harmed by natural weather. This damage happens faster in places where acid rain is a problem.

Fires can also damage stone in buildings. High temperatures can change the stone, making it weaker. When firefighters use water to put out a fire, it can cause more damage to the stone. Good design choices, like special rain coverings and proper heating and cooling systems, can help protect buildings from weather damage.

Soil

Granitic rock, the most common rock on Earth, changes in a special way when it weathers. It loses some minerals and turns into a mix of clay and iron oxides. This makes the soil have less calcium, sodium, and some iron than the original rock. But it has more aluminium, potassium, and titanium.

Basaltic rock weathers faster than granitic rock. In warm, wet places, it turns into clay and other minerals. In rainy areas, it can become a material called bauxite, which is used to make aluminium. Soil takes between 100 and 1,000 years to form, which is a short time compared to Earth's history. Some rock layers show many old soil layers, called paleosols. These help scientists learn about the past.

Wood, paint and plastic

Wood, like rocks and minerals, can change over time because of water and air. Sunlight can damage wood and also make paint and plastics look old and worn.