These scientists have basically looked at the rate of evolution and concluded that if life was advancing at a constantly steady rate (in the same way that the number of transistors we can fit on a chip doubles every 18 months, or 2 years or whatever), then life is older than the earth.
http://www.technologyreview.com/view/513781/moores-law-and-the-origin-of-life/
http://www.technologyreview.com/view/513781/moores-law-and-the-origin-of-life/
