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Science

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Soil Formation—Physical and Chemical Weathering

Run Time: 00:04:23

On the Big Island of Hawaii, lava from volcanoes forms new rock. Physical processes—including rain, plant rooting, freezing and thawing, and the pounding of ocean waves—all contribute to weathering: the breakdown of rock into smaller particles known as sediment, which can lead to the formation of soil. To further explore how lava flows in Hawaii can be converted to lush, tropical forests, geologist Andy Kurtz of Boston University describes the process of chemical weathering. Carbon dioxide dissolved in rainwater makes a weak acid. Acidic rain chemically alters source rock and speeds physical weathering to produce a chemically distinct material, clay. Soil begins to form when sand, clay, silt, and organic material accumulate in cracks in the lava. Featured Scientists: Oliver Chadwick, Ph.D., Andy Kurtz, Ph.D., and Elissa Levine, Ph.D.

Standards

NSES Standard

Grades 5-8 Standard D. Soil consists of weathered rocks and decomposed organic material from dead animals, plants, and bacteria, that have different chemical compositions and textures. And also: Some changes in the solid earth can be described as the "rock cycle."


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