The saying, 'Men are from Mars and women are from Venus,' may be correct than a lot of people think. While modern Earth seems unique in its ability to support life, pre-historic Earth was almost certainly not so friendly, so how could the fragile, early forms of life developed here? Some scientists believe it did not and now researchers at the European Association of Geochemistry and Goldschmidt Conference have found evidence to support that idea.
About three billion years ago, the Earth was a very different place with far more of its surface covered in water, and very little oxygen in its atmosphere. This poses some interesting problems as RNA, which is believed to be one of the first genetic molecules, is damaged by water. Also organic molecules have the tendency of turning into tar when energy is added to them, though some materials like boron and oxidized molybdenum can inhibit this, but they are not common in wet environments. Mars three billion years ago though had less water on its surface and did have boron and oxidized molybdenum, as has been recently discovered through the analysis of a Martian meteorite.
If this interpretation of the evidence is correct, then the first genetic molecules needed for life likely formed on Mars, and then were caught on a rock which left the fourth planet for the third, apparently at a time more supporting of life. From then on these earliest forms of life adapted to the Earth and Earth adapted to them, eventually having the oxygen-rich atmosphere we all breathe today.