Start with an unproven (but plausible) hypothesis: that the complexity of life grows at a constant exponential rate, just as so many other natural processes do. Or, if you will, just like Moore's Law of integrated circuit complexity. Then extrapolate backwards – given the complexity of life today, and an observed rate of growth, when did life have a complexity of 1 (that is, when did life begin)?
Two scientists have done this math, and have arrived at a date of roughly 9.5 billion years ago. That's well before the Earth (or the Sun, for that matter) existed.
What does this mean?
One very real possibility is that the scientists are mistaken for some reason. After all, they don't have any direct observational evidence for this date, just the extrapolation of a hypothesis – very weak ground to rest a theory on.
The other possibility is that they are correct, and that would mean that life originated before the Earth did – and that the Earth was “seeded” with life through some mechanism (comet collisions are a frequently cited candidate).
It's an interesting ponder...