You're exactly right. Things happen at such vast time scales; we have nothing to go by except the fossilized results. For example, did the vertical strata of certain rock formations occur over eons or as the result of some cataclysmic event? I think our scientists are biased toward the former because the latter is unthinkable in the context of human affairs.
You mentioned the molten interior, but what I believe is even more of a factor is the solid core. It spins faster than the surface. How is that possible? Good question. Researchers believe it catches up with the surface once every 400 years; for this to be true, the solid core must be rolling along inside of the earth's interior, if you will, rather than suspended. And since the solid core's circumference is smaller than the inner surface (whatever it might consist of (i.e., magma)), the solid body turns faster.
My pet theory is that magma reaching the surface is pumped to the surface by the solid inner core rather than rising through convection. And most of the interior heating is due to friction from tidal forces inside the earth.
Another of my theories is that heat builds up over eons until it gets released during cyclic cataclysm events, probably occurring about every 100 thousand years or so.
I think these events are what causes the ice ages to begin again. And since it has been about 100 thousand years since the last ice age began, we could be due for the start of another one.
I remember when Mount Saint Helens erupted. The geologist quoted by the Oregonian said we had just witnessed 10,000 years of geological movement in one day.