Bioturbation: How Plants and Animals Change the Surface of the Planet

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One of the agents of organic weathering, bioturbation is the disturbance of the soil or sediment by living things. It may include displacing soil by plant roots, digging by burrowing animals (such as ants or rodents), pushing sediment aside (such as in animal tracks), or eating and excreting sediment, as earthworms do. Bioturbation aids the penetration of air and water and loosens sediment to promote winnowing or washing (transportation).

How Bioturbation Works

Under ideal circumstances, sedimentary rock is formed in predictable layers. Sediments -- bits of soil, rock, and organic matter -- collect on the surface of the land or at the bottom of rivers and oceans. Over time, these sediments are compressed to the point of which they form rock. This process is called lithification. Layers of sedimentary rock may be seen in many geological structures.

Geologists are able to determine the age and composition of sedimentary rock based on the materials included in the sediment and the level at which the rock lies. In general, older layers of sedimentary rocks lie under newer layers. Organic matter and fossils that make up the sediments also provide clues to the age of the rock.

Natural processes can disturb the regular layering of sedimentary rock. Volcanoes and earthquakes can disturb layers by forcing older rock closer to the surface and newer rock deeper into the Earth. But it doesn't take a powerful tectonic event to disturb sedimentary layers. Organisms and plants are constantly shifting and changing Earth's sediments. Burrowing animals and the actions of plant roots are two sources of bioturbation.

Since bioturbation is so common, sedimentary rocks are divided into three groups that describe their level of bioturbation:

  • Burrowed rock is filled with evidence of organisms, and may contain elements from several different sedimentary layers.
  • Laminated rock shows evidence of bioturbation at the surface caused by non-burrowing activity. Examples include furrows and tracks created by aquatic or terrestrial animals.
  • The massive rock contains sediments from just a single layer.

Examples of Bioturbation 

Bioturbation occurs in many different environments and at several different levels. For example:

  • Earthworms digging through soil can shift older materials to higher layers. They can also leave behind traces of their activity in the form of fecal matter which, over time, lithifies.
  • Burrowing marine animals such as crabs, clams, and shrimp, can radically change sedimentary layers. These animals burrow into the sand, creating tunnels and moving materials from one sedimentary layer to another. If the tunnels are sturdy enough, they may later be filled with material formed at a later time.
  • Tree roots often run through multiple layers of soil. As they grow, they may disturb or mix sediments. When they fall, they pull older materials to the surface.

Significance of Bioturbation

Bioturbation provides researchers with information about sediments, and thus about the geology and history of the sediments and the area. For example:

  • Bioturbation can suggest that a particular area is likely to be rich in petroleum or other natural resources;
  • Bioturbation can provide clues to ancient life in the form of fossilized animal and plant remains;
  • Bioturbation can provide information about life cycles, dietary habits, and migration patterns of contemporary organisms.
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Alden, Andrew. "Bioturbation: How Plants and Animals Change the Surface of the Planet." ThoughtCo, Apr. 5, 2023, Alden, Andrew. (2023, April 5). Bioturbation: How Plants and Animals Change the Surface of the Planet. Retrieved from Alden, Andrew. "Bioturbation: How Plants and Animals Change the Surface of the Planet." ThoughtCo. (accessed June 2, 2023).