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Difficulty: EasyRocks, Minerals, and Soil

A mature soil profile develops distinct horizontal layers as parent material weathers over time. What is the correct sequence of these primary soil layers when arranged from the ground surface downward to the deepest level?

  1. 1Organic surface layer and topsoil containing decaying matter
  2. 2Subsoil layer rich in accumulated minerals and clay
  3. 3Partially weathered parent rock fragments
  4. 4Solid, unweathered bedrock foundation

Answer

The correct sequence from the surface to the deepest layer is: Organic surface layer and topsoil, followed by the subsoil layer, then partially weathered parent rock fragments, and finally solid, unweathered bedrock.
In a standard soil profile arranged from the surface downward, the layers progress from the organic-rich topsoil at the surface, to the mineral-accumulating subsoil beneath it, followed by partially broken parent material, and ending with solid bedrock at the lowest depth.

Step-by-Step Solution

1
Identify the uppermost layer at the ground surface.
The organic surface layer and topsoil are placed first.
Plant litter, humus, and biological activity are concentrated at the ground surface in direct contact with the atmosphere.
2
Identify the intermediate mineral layer located beneath the topsoil.
The subsoil layer is placed second.
Downward-percolating rainwater leaches soluble minerals and clay particles from the topsoil and deposits them into this zone of accumulation.
3
Identify the transition layer directly above the solid rock base.
Partially weathered parent rock fragments are placed third.
This layer consists of large rock chunks undergoing mechanical breakdown from the underlying solid rock.
4
Identify the deepest, unaltered base of the profile.
Solid, unweathered bedrock is placed fourth.
Bedrock is the foundational, unweathered rock layer that serves as the parent material for the soil layers above.

Key Concept

Vertical sequence of horizons in a mature soil profile from the surface to bedrock
Estimated Time:45s
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Topics

Rocks, Minerals, and Soil

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