There are several hypotheses, including warming or cooling of Earth, changes in seasonal fluctuations or ocean currents, and changing positions of the continents.
有几种假说，包括地球变暖或变冷，季节波动或洋流的变化，以及大陆位置的变化。
The radial velocity method, which looks for changes in a star's velocity toward or away from Earth triggered by a planet's orbit around that star.
径向速度法，即观察某颗行星环绕恒星的轨道所引起的恒星相对地球来往的速度变化。
Theories range from the extinction of the mammoth to sudden environmental changes caused by a comet impacting or earth or the break of a massive freshwater lake, lake Agassiz.
这些理论包括猛犸象的灭绝、因彗星或地球引起的环境剧烈变化、以及阿加西湖淡水的减少。
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