Genesis 6:2: "... the sons of God saw that the daughters of humans were beautiful, and they married any of them they chose." In some Hebrew understanding and in many Bibles, the term 'sons of God' is interpreted as 'angels'. In other words, there were aliens way back then, who not only came to earth, but were able, and did get together with human woman. The "Book of Enoch," which is considered to NOT be part of the Bible, explains a whole lot about these angels/aliens. What they did was something that God had NOT wanted done, and He punished them severely for it - including their death. The point is that there may be all kinds of alien objects around. But more than likely, God got rid of most of them, because He wants people to inhabit the earth, not angels.