Organic (Biological) Weathering Explained

Organic (Biological) Weathering Explained Organic weathering, also called bioweathering or biological weathering, is the general name for biological processes of weathering that break down rocks. This includes the physical penetration and growth of roots and digging activities of animals (bioturbation), as well as the action of lichens and moss on various minerals.   How Organic Weathering Fits Into the Larger Geological Picture Weathering is a process by which surface rock breaks down. Erosion is a process by which weathered rock is moved by natural forces such as wind, waves, water, and ice. There are three types of weathering: Physical or mechanical weathering (for example, water gets into cracks in rock and then freezes, pushing against the rock from the inside);Chemical weathering (for example, oxygen interacts with iron in rocks, causing the iron to turn to rust and thus weakening the rock)Organic or biological weathering (for example, the roots of a tree grow into boulders in the soil and splitting the boulders apart over time) While these different types of weathering can be described as different from one another, they also work together. For example, tree roots may split boulders more easily because the rocks have been weakened as a result of chemical or physical weathering.   Plant-Related Biological Weathering Tree roots, because of their size, cause a significant amount of biological weathering. But even much smaller plant-related actions can weather rocks. For example: Weeds pushing through road surfaces or cracks in boulders can expand gaps in the rock. These gaps fill with water. When the water freezes, the roads or boulders crack. Lichen (fungi and algae living together in a symbiotic relationship) can cause a great deal of weathering. Chemicals produced by fungi can break down the minerals in rocks. Algae consume the minerals. As this process of breakdown and consumption continues, rocks start to develop holes.  As described above, holes in rocks are vulnerable to physical weathering caused by the freeze/melt cycle. Animal-Related Biological Weathering Animal interactions with rock can cause significant weathering. As with plants, animals can set the stage for further physical and chemical weathering. For example: Tiny burrowing animals secrete acids or scrape their way into rock to create rocky burrows. This process weakens the rock and actually starts the weathering process.Larger animals leave feces or urine on rock. The chemicals in animal waste can corrode minerals in rock.Larger burrowing animals shift and move rock, creating spaces where water can accumulate and freeze. Human-Related Biological Weathering Human beings have a dramatic weathering effect. Even a simple path in the woods has an impact on the soil and rocks that make up the path. Major changes affected by humans include: Construction moving, scoring, and smashing rock for construction of buildings and transportation systemsMining massive projects involve stripping entire hillsides or making major changes to or removing rock from under the surface of the EarthAgriculture in addition to moving rocks to make farming possible, human beings also change the composition of the soil through fertilization and application of herbicides.

Understanding Experimental Groups

Understanding Experimental Groups Scientific experiments often include two groups: the experimental group and the control group. Heres a closer look at the experimental group and how to distinguish it from the experimental group. Key Takeaways: Experimental Group The experimental group is the set of subjects exposed to a change in the independent variable. While its technically possible to have a single subject for an experimental group, the statistical validity of the experiment will be vastly improved by increasing the sample size.In contrast, the control group is identical in every way to the experimental group, except the independent variable is held constant. Its best to have a large sample size for the control group, too.Its possible for an experiment to contain more than one experimental group. However, in the cleanest experiments, only one variable is changed. Experimental Group Definition An experimental group in a scientific experiment is the group on which the experimental procedure is performed. The independent variable is changed for the group and the response or change in the dependent variable is recorded. In contrast, the group that does not receive the treatment or in which the independent variable is held constant is called the control group. The purpose of having experimental and control groups is to have sufficient data to be reasonably sure the relationship between the independent and dependent variable is not due to chance. If you perform an experiment on only one subject (with and without treatment) or on one experimental subject and one control subject you have limited confidence in the outcome. The larger the sample size, the more probable the results represent a real correlation. Example of an Experimental Group You may be asked to identify the experimental group in an experiment as well as the control group. Heres an example of an experiment and how to tell these two key groups apart. Lets say you want to see whether a nutritional supplement helps people lose weight. You want to design an experiment to test the effect. A poor experiment would be to take a supplement and see whether or not you lose weight. Why is it bad? You only have one data point! If you lose weight, it could be due to some other factor. A better experiment (though still pretty bad) would be to take the supplement, see if you lose weight, stop taking the supplement and see if the weight loss stops, then take it again and see if weight loss resumes. In this experiment you are the control group when you are not taking the supplement and the experimental group when you are taking it. Its a terrible experiment for a number of reasons. One problem is that the same subject is being used as both the control group and the experimental group. You dont know, when you stop taking treatment, that is doesnt have a lasting effect. A solution is to design an experiment with truly separate control and experimental groups. If you have a group of people who take the supplement and a group of people who do not, the ones exposed to the treatment (taking the supplement) are the experimental group. The ones not-taking it are the control group. How to Tell Control and Experimental Group Apart In an ideal situation, every factor that affects a member of both the control group and experimental group is exactly the same except for one the independent variable. In a basic experiment, this could be whether something is present or not. Present experimental; absent control. Sometimes, its more complicated and the control is normal and the experimental group is not normal. For example, if you want to see whether or not darkness has an effect on plant growth. Your control group might be plants grown under ordinary day/night conditions. You could have a couple of experimental groups. One set of plants might be exposed to perpetual daylight, while another might be exposed to perpetual darkness. Here, any group where the variable is changed from normal is an experimental group. Both the all-light and all-dark groups are types of experimental groups. Sources Bailey, R.A. (2008). Design of Comparative Experiments. Cambridge: Cambridge University Press. ISBN 9780521683579. Hinkelmann, Klaus and Kempthorne, Oscar (2008). Design and Analysis of Experiments, Volume I: Introduction to Experimental Design (Second ed.). Wiley. ISBN 978-0-471-72756-9.