How does solid rock break down at Earth's surface, and how does soil form?
Distinguish physical from chemical weathering, explain the factors that control the rate of weathering (climate, surface area, rock type), and describe how weathering and other processes form soil.
A Regents answer on weathering and soil: physical (mechanical) weathering such as frost wedging versus chemical weathering such as carbonation and oxidation, how climate, surface area and rock type control the rate, why warm wet climates weather chemically faster, and how soil forms as a mix of weathered rock and organic matter, with worked exam questions.
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What this topic is asking
The Regents wants you to distinguish physical from chemical weathering, explain the factors that control the rate of weathering (climate, surface area, rock type), and describe how soil forms. The defining distinction is that weathering breaks rock in place, while erosion (the next topic) moves the pieces.
Physical versus chemical weathering
Common physical weathering processes:
- Frost wedging: water seeps into cracks, freezes and expands (about 9 percent), prying the rock apart. Common in New York's freeze-thaw climate.
- Abrasion: rock surfaces are worn by the rubbing of wind-blown sand, water-carried sediment or glaciers.
- Root action and burrowing: growing roots and animals widen cracks.
Common chemical weathering processes:
- Carbonation: carbon dioxide dissolves in rainwater to form weak carbonic acid, which dissolves calcite in limestone and marble (forming caves and karst).
- Oxidation: oxygen reacts with iron-bearing minerals to form iron oxides (rust), giving red-brown colors.
- Dissolving: soluble minerals such as halite dissolve directly in water.
What controls the rate of weathering
How soil forms
Soil that forms in place directly from the bedrock below it is residual soil and tends to match the local bedrock; soil formed from material carried in from elsewhere (by water, wind or ice) is transported soil and may not match the bedrock beneath it. New York's soils are largely transported, left by the glaciers.
Try this
Q1. State one difference between physical and chemical weathering. [1 point]
- Cue. Physical weathering breaks rock into smaller pieces without changing its chemistry; chemical weathering changes the minerals into new substances.
Q2. Explain why a warm, humid climate produces faster chemical weathering than a cold, dry one. [2 points]
- Cue. Chemical reactions need water and speed up with temperature, so abundant water and heat in a warm, humid climate accelerate the breakdown of minerals.
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (style)1 marksPart A. Water seeps into a crack in a rock, freezes overnight, and the crack widens. Over many cycles the rock splits apart. This is an example of (1) chemical weathering by carbonation (2) physical weathering by frost wedging (3) erosion by running water (4) deposition. Justify your choice.Show worked answer →
A 1-point multiple-choice question. The answer is (2).
Water expands about 9 percent when it freezes, so repeated freezing in a crack pries the rock apart without changing its chemistry; this is physical (mechanical) weathering called frost wedging. It is not chemical weathering (1, which changes the minerals), not erosion (3, which is transport of the broken pieces), and not deposition (4, which is dropping sediment). The trap is calling any rock breakdown "erosion"; weathering breaks rock in place, erosion moves it.
Regents (style)3 marksPart C. Two identical limestone gravestones are placed in a hot, humid climate and a cold, dry climate. (a) State which gravestone will chemically weather faster and explain why. (b) Explain how breaking a rock into smaller pieces changes its rate of weathering. (c) Identify one gas in the atmosphere that makes rainwater slightly acidic and speeds chemical weathering of limestone.Show worked answer →
A 3-point extended-response question.
(a) 1 point: the gravestone in the hot, humid climate weathers chemically faster, because chemical reactions speed up with more water and higher temperature.
(b) 1 point: breaking a rock into smaller pieces increases its total surface area exposed to air and water, so it weathers faster.
(c) 1 point: carbon dioxide (it dissolves in rainwater to form carbonic acid, which dissolves the calcite in limestone). Accept reasoning about acid rain from sulfur or nitrogen oxides.
Markers reward the warm-wet faster reasoning, the surface-area effect, and carbon dioxide/carbonic acid (or a valid acid-rain answer).
Related dot points
- Identify the agents of erosion (running water, glaciers, wind, waves and gravity) and use the characteristic shapes and deposits of sediment to infer which agent transported it.
A Regents answer on erosion: the agents that transport sediment (running water, glaciers, wind, waves, gravity), why running water is the dominant agent, the tell-tale evidence each agent leaves (rounded versus angular particles, scratched and grooved bedrock, V-shaped versus U-shaped valleys, sorted versus unsorted deposits), with worked exam questions.
- Explain how deposition occurs as transporting agents lose energy, and use the Reference Tables relationship of particle size to water velocity, together with particle size, shape and density, to predict settling order and sorting.
A Regents answer on deposition and sorting: how sediment is dropped when a transporting agent slows, the Reference Tables graph of transported particle size versus water velocity, why larger and denser particles settle first, horizontal and vertical sorting, graded bedding, and how rounded versus angular shape affects settling, with worked exam questions.
- Define a mineral and explain how physical properties (hardness, cleavage, luster, streak, color and density) and chemical composition are used to identify minerals, using the relevant Reference Tables charts.
A Regents answer on minerals: the definition of a mineral, the physical properties used to identify them (hardness, cleavage and fracture, luster, streak, color, density), why composition and internal arrangement control those properties, and how to use the Reference Tables Properties of Common Minerals chart, with worked exam questions.
- Describe the rock cycle and explain how igneous rocks form from cooling magma or lava, using the Reference Tables Scheme for Igneous Rock Identification to relate texture, composition, color and density to the rock name.
A Regents answer on the rock cycle and igneous rocks: the three rock families and the processes that link them, how cooling rate controls crystal (grain) size, how the Scheme for Igneous Rock Identification relates texture, mineral composition, color and density to a rock name (granite, basalt, obsidian and others), with worked exam questions.
- Explain how landscapes are classified (mountains, plateaus, plains) by elevation, relief and structure, how climate and bedrock control landscape development, and use the Reference Tables map of New York's landscape regions.
A Regents answer on landscapes: how mountains, plateaus and plains are classified by elevation, relief and rock structure, how climate (arid versus humid) and bedrock resistance shape landscape development, stream drainage patterns, and how to use the Reference Tables Generalized Landscape Regions and Bedrock Geology maps of New York, with worked exam questions.
Sources & how we know this
- Reference Tables for Physical Setting/Earth Science (2011 edition) — New York State Education Department (2011)
- Regents Examination in Physical Setting/Earth Science — New York State Education Department (2026)