State of the planet· The columns of time
Magma ocean
4.54 Ga → 4.4 Ga
The surface is molten, kept that way by accretion and then by the giant impact that formed the Moon.
What the evidence shows
For its first hundred and forty million years the Earth has no surface in any ordinary sense. Rock is molten to great depth, kept that way by the heat of accretion and then by the impact that formed the Moon. Nothing from this state survives. What dates its end is a mineral from what came after: zircons from the Jack Hills of Western Australia, at about 4.4 billion years, whose oxygen isotopes record interaction with liquid water at low temperature. Cool enough for water is also cool enough for a crust. This band is a backdrop as well as a regime, and the picture drawn over it keeps the same restraint: no cones, no vents, no horizon, nothing in the sky. The heavy bombardment of the early Earth is real, but streaks of infalling debris came out as suspended lines that read as rain, and a picture that says the wrong thing clearly is worse than one that says less.
Bounds and conventions
Nothing dates the end of the molten state directly, because a molten surface leaves no rock to date. The zircon that fixes it formed after the fact, in a crust that already existed, so it gives a latest possible date and no earliest one: the ocean of magma may have set a hundred million years before that grain and left no way to tell.