From: Stevie Ray
Location: Montreal Quebec Canada
Hi there. Lately I've been thinking about the fact that the solar system appears to have been formed by an accretion disc rather than the sun forming in a stellar nursery and then 'acquiring planets' over time-its unlikely a complex planetary system could be formed that way anyway. That would make the real age of the solar system 13.25 billion years or so & our planet 12.5 billion years old due to the fact the big bang took 750,000 years to coalesce via the accretion disc principal into recognizable/ordered planetary systems of which there are 'infinity minus one' in number....Geological 'churn' might explain the lack of 'surface evidence' dating back earlier than 4 billion years-which could suggest there has been many sentient species originating on Earth over millenia-and we are the most recent-but all traces of past races would have long 'churned' back into the Earth & oblivion forever-unless we can find something in actual space itself.... All the prior races might also have become extinct billions of years ago also, Its the ultimate mystery. Or very close. Take care.
From: Greg Bear
Not sure we can stretch Earth's history back that far. There is the half-life of radioactive thorium and latent heat in the core to deal with. But geological churn could indeed erase a lot of early evidence! Besides, the nebular theory creates both sun and planets out of the spinning disk, though it's possible others could be acquired later.