关键词: 水土流失, 基础研究, 土壤侵蚀过程, 地球, 近地天体, 巡天, 飞船, 陨击, 危害分析, 防御对策, 预警

Abstract:
The earth inhabits a hazardous environment. “Near Earth Objects（NEO）”，whose orbits approach Earth’s orbit, could pose potential hazard of striking Earth. In fact, since its birth, the earth is continually bombarded by these objects. The scarred countless impact craters from Moon and Mercury are the best evidence. Because of a serious evolution of the Earth and  the remains of the old impact craters being wiped out, only more than 170 impact structures are identified. Fortunately, the impacts from the objects at this stage are mostly in smallscale , their hazards are not too serious. However, an impact event is difficult to predict. Once the event  of a larger impact occurs, they will result in much more serious than the big earthquake hazards. The event of the comet colliding with Jupiter in 1994 shocked the whole world, and  enlightened people to pay more attention to the dangers of the earth by such impact. In fact, there are some recent examples：Tunguska explosion event in 1908; the Jilin meteorite shower in 1976; the asteroid 2008 TC3 fallen in Sudan in 2008. Earlier 2010, the U.S. Academy of Sciences announced, “defend the Earth: nearearth objects survey and mitigation of risk strategy for the final report”. Combined with relevant information，the real scientific knowledge and mitigation of risk strategy are introduced briefly to the public understanding and to avoid seriously misleading from the distorted video.

Key words: soil and water loss, basic research, soil erosion process, 973 program , Earth, near earth object, survey, spacedraft, impact, risk analysis, hazard mitigation strategy, warning