Isostasy Theory of Aren Diacen Pratt (A. D. Pratt)
The theory of Isostasy is based on the idea that there is a balance between the high mountains and low plateaus and plains of the earth. Geologists have presented this theory of Isostasy in various ways. Geologist G. B. Airy presented a Isostasy theory about the earth's equilibrium. In 1859, geologist Aren Diacen Pratt (A. D. Pratt) presented another theory of Isostasy against this theory given by Airy. The theory of Isostasy presented by A. D. Pratt mensioned below:
A. D. Pratt's theory: According to geologist A. D. Pratt, the density of all parts of the earth is not equal. Pratt states in his theory that all parts of the Earth's solid surface are floating on the same plane above the fluid substratum inside the Earth. However, the surfaces of the earth's solid ground are located at different heights and have created equilibrium conditions. Pratt also points out that the parts of the Earth's solid surface that have the lowest density are the parts that elevated more above the Earth's surface. On the other hand, the densest parts of the Earth's solid surface are the least elevated parts. This concept presented by A. D. Pratt is also called Level of Compensation.
|Fig-1: According to A. D. Pratt, Mountains are higher because they are made of lighter material than Plains.|
|Fig-2: A. D. Pratt's First experiment on Isostasy as per Fig-1.|
|Fig-3: A. D. Pratt's Second experiment on Isostasy as per Fig-1.|
As can be seen in Figure 3, the blocks (P1, P2 and P3) of equal cross-section and weight are positioned on the same level in the fluid and are balanced at different heights above. The blocks removed the same amount of fluid. So, the lower the density of the block, the higher its height at the top.
Presented by Md. Shahin Alam