Weathering

Weathering is the process by which rocks, soils, and minerals break down and change over time. This happens when they come into contact with water, air, sunlight, and living things. Unlike erosion, which moves these materials away, weathering happens right where the rocks are, without much movement.

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

When rocks weather away, they mix with organic material to form 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

Physical weathering, also called mechanical weathering, is the process that breaks rocks into smaller pieces without changing their chemical makeup. This happens mainly through temperature changes. For example, when water inside cracks in rocks freezes, it expands and pushes the cracks wider. This is called frost weathering and is a very common way rocks break apart.

Another way rocks break apart is through thermal stress. When rocks heat up during the day and cool down at night, they expand and contract. Over time, this constant changing can cause the rock to split into pieces. This process is especially important in places with big temperature differences, like deserts. Rocks can also break apart when pressure from deep underground is released, allowing the rock to expand and split. Living things like plants and lichens can also help break rocks apart by growing in cracks and pushing them open.

Chemical

Most rocks form deep underground under high temperature and pressure. When they reach the surface, they meet cooler, wetter conditions that change them slowly. Water, oxygen, and carbon dioxide in the air and rain react with the rocks, breaking them down and altering their minerals. This process is called chemical weathering.

Water is the main force behind chemical weathering. It helps turn many minerals into clay or other substances. Oxygen also plays a role by changing some minerals. Carbon dioxide mixes with water to form a weak acid that can dissolve certain rocks like limestone. Living things, like plants and tiny organisms in soil, can also speed up this process by releasing acids and gases that break down minerals.

Ocean floor

Weathering of the ocean floor happens differently than weathering on land. It is a slow process, with basalt rock becoming 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

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

Fires can also damage stone in buildings. High temperatures can change the stone in many ways, making it weaker. When firefighters use water to put out a fire, it can cause more damage to the stone. These issues can be dangerous for both the environment and people inside the building. 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 type of rock on Earth's surface, breaks down in a specific way when it weathers. It starts by losing certain minerals and ends up turning into a mix of clay and iron oxides. This process makes the soil have less calcium, sodium, and some iron compared to the original rock, but more aluminium, potassium, and titanium.

Basaltic rock weathers more quickly than granitic rock because of how it forms and its texture. In warm, wet places, it turns into clay and other minerals. In areas with lots of rain, 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 in terms of Earth's history. Some rock layers show many old soil layers, called paleosols, which can help scientists study the past.

Wood, paint and plastic

Wood, like rocks and minerals, can change over time due to water and air. It is especially affected by sunlight, which can damage its surface. This same sunlight can also wear down paint and plastics, making them look old and damaged.