The correct answer is - A. Desertification is increasing, and the desert is expanding.
The Sahara desert has been expanding in the past decades, and it has started to overtake territory south of it. This is mainly due to climate changes, the precipitation has been decreasing, the temperatures have been rising, so the desert has slowly crippled into the territories that were once steppes and savannas. There is an organized action from the people that leave on the borderline of the desert, where they have been thought some techniques as to how to stop the desert growing, and they have gladly accepted it and work hard on it. Initially it seems that there are positive results, but for sure only the time will tell.
A drainage basin is a region of land where water from rain or snowmelt flows into an ocean, lake, river, or other body of water.
the oldest ocean floor is only 180 million years old, because the oldest crust is destroyed at subduction zones.
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What are subduction zones?</h3>
According to NOAA, tectonic plates are fragments of the Earth's hard outer layer that steadily travel across the surface of the globe over millions of years (opens in new tab). (This is a fundamental principle of the theory of plate tectonics, which holds that pieces of the Earth's crust slide across the lower mantle and carry continents with them.) According to the U.S. Geological Survey(opens in new tab), the Earth's crust and the top part of the mantle, a thick, heated layer under the crust, make up that outer layer, also known as the lithosphere (USGS). This lithosphere material curls downward into the heated mantle during subduction zones, when two tectonic plates collide and one slides beneath the other.
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