有生源说，胚种论一种学说，认为来自宇宙空间的微生物或生物化学物是地球上生命的起源，并且在宇宙的其他部分可能有适合的大气状况存在 The theory that microorganisms or biochemical compounds from outer space are responsible for originating life on Earth and possibly in other parts of the universe where suitable atmospheric conditions exist.
月球为地球所吸引，但由于宇宙空间中其他天体相反的引力，月球保持了固定的轨道。 The moon gravitates to the earth, but is held in its path by opposing forces from other bodies in space.