Hi All

Guys, the current age for the Earth & Sun from geochronology and solar modelling is 4.567 gigayears.

The Sun formed quickly in astrophysical terms - spending a mere ~ 50 megayears undergoing Helmholtz contraction and burning lithium/deuterium before hitting the Main Sequence. To get to the point where its opacity slowed down its initial free-fall collapse as a gas cloud took just a few thousand years - once it'd heated up to ~ 400 K or so it was on the Helmholtz Collapse line.

The giant planets had to form before the proto-solar nebula blew away taking all the H/He gas with it - within 3 - 10 million years, depending on estimates. If they formed via gravitational instability, like the Sun, then they took a mere ~ 1000 years to hit their stable contraction phase. If they had to accrete a Neptune-sized core first then that had to be within ~ 1 - 2 million years.

The dating of the Earth-Moon making impact has been constrained to within ~ 50 million years of the birth of the Earth by isotopic proxies. The rock-vapour atmosphere that followed would have cooled and condensed within a few thousand years - oceans would've condensed within ~ 1 million years.

gbaikie was wrong about the ~ billion years. Even the slowest accretion scenarios for the terrestrial planets take just a 100 million. Other scenarios are quite quick - for example the Capture/Collision scenario has the initial giant planets collapsing and forming moons within ~ 1000s of years. The two innermost planets collide and their cores form Earth/Venus - Mercury, Mars and possibly Theia (the Moon-maker), were satellites of one of the planets. Mercury was close enough to the collision to be abraded down to almost its core. Mars was battered enough to have its current hemispherical anomaly. All this occurred while a captured disk decayed away around the Sun within ~ 3 million years.

Adam