The phenomenon of wearing down of relief variations of the surface of the earth through erosion is known as Gradation.

Erosion is a natural process that occurs when the surface of the Earth is worn away by the action of water, wind, ice, or other geological agents. This process leads to the gradual wearing down of relief variations on the Earth's surface, resulting in a more uniform and level landscape. This phenomenon is known as gradation.

Explanation:
The process of gradation involves the constant movement and transportation of rock particles and soil from one place to another. It is a combination of several erosion processes, including weathering, transportation, and deposition.

1. Weathering:
Weathering is the initial step in the process of gradation. It refers to the breakdown and decomposition of rocks and minerals by various physical, chemical, and biological processes. These processes include the action of water, temperature changes, pressure changes, and the activity of living organisms. Weathering weakens the rocks and makes them more susceptible to erosion.

2. Transportation:
Once the rocks and minerals are broken down into smaller particles through weathering, they are transported by various agents such as water, wind, ice, and gravity. Water is the most common agent of transportation and can carry rock particles over long distances. Wind can transport smaller particles like sand and dust, while ice can transport larger particles during glaciation.

3. Deposition:
Deposition is the final stage of the gradation process. It occurs when the transported rock particles and sediment settle down and come to rest. This usually happens when the transporting agent loses its energy and can no longer carry the particles. Deposition can result in the formation of sedimentary layers and the accumulation of soil in new locations.

Effects of Gradation:
The process of gradation has several effects on the Earth's surface:

- Smoothing of landforms: Gradation leads to the smoothing of irregularities in the Earth's surface, resulting in a more uniform and level landscape.
- Formation of valleys and basins: Gradation can result in the formation of valleys and basins as erosion wears away the land between higher areas.
- Creation of sedimentary deposits: The process of deposition during gradation can lead to the formation of sedimentary deposits, which can contain valuable resources such as minerals, fossils, and groundwater.
- Shaping of coastlines: Gradation plays a significant role in shaping coastlines through the erosion and deposition of sediment by waves and currents.

In conclusion, gradation is the process by which relief variations on the Earth's surface are gradually worn down through erosion. It involves weathering, transportation, and deposition of rock particles and sediment, resulting in a more uniform and level landscape.