'Climatic variations' and 'Human activities' can be regarded as the two main causes of desertification. removal of the natural vegetation cover（by taking too much fuel wood）, agricultural activities in the vulnerable ecosystems of arid and semi-arid areas, which are thus strained beyond their capacity.
The answer is D. The Palaeozoic era was characterized by the supercontinent of Pannotia which was located at the current position where Chile is, 500 million years ago. There is evidence that shows that central Africa was once at the polar regions due to evidence of glaciers in its geological rocks. Due to tectonic movement, the Appalachians and the Ural Mountains were formed in the resulting Pangea supercontinent.
Answer:
Mercury has the widest variation in surface temperatures between night and day of any planet in the solar system.
Explanation:
Answer:
1.The presence of dense tropical forest provides ready sources of valuable timber.
2.Presence of many economic trees.
3.Presence of wide market for timber products within the country.
4.High demand for hardwood in foreign counties.
