Answer:
Approximately 4.5 billion years ago (The Hadean Eon) .
Explanation:
The Geologic Timescale's "Hadean" era, named for Hades (Hell, well, we weren't feeling very imaginative that day), encompasses the Earth's origins. According to the evidence we currently have, the Earth's surface at that time was mostly made up of lava lakes and molten rock.
How would that appear? The first 500 Ma of Earth's history have left very little stuff behind. You may, however, take a peek at our moon, which similarly went through a lava lake period before freezing. You'll see that it has both dark and bright landscape.
The lighter material is known as highlands and is primarily composed of anorthosite. Anorthose, a kind of plagioclase feldspar, is the main component of the igneous rock known as anorthosite. According to what we know, the Moon too had a lava lake era. Liquid rocks exposed at the surface were cooling and fractionally crystallizing throughout this lengthy period. A certain order of minerals was developing. And these minerals were dividing up according to the density of the melt; less dense minerals, like plagioclase (Anorthose is a plagioclase), floated to the surface in a sort of incandescent crystal slush slurry and formed a sort of lid there. Denser minerals, like olivines, were sinking to the bottom of the lava lake to form cumulates. As the lava lakes cooled, anorthosite piled on top in successive layers, thickening the mass of floating crystals. Large meteor impacts occasionally pierced this anorthosite crust, and part of the thicker (and darker) underlying liquid accumulated in the ensuing craters to produce those roundish dark patches (Maria), which are now filled with basalt.
After the lava lakes froze/crystallized over, such characteristics were maintained since there was no significant tectonic activity on the Moon (except for the local meteor impacts which screw things up a bit).
