So ...how long do you reckon Earth has been doing this?
Long enough for you to make your next statement. However, before you do so, make sure you familiarise yourself with basic Special Relativity, most importantly the Lorentz transformation.
The equivalence principle, gravity, acceleration and so on are all part of general relativity. Special relativity only deals with reference systems that have relative velocity regarding each other.
The term "general relativity" was introduced to point out, that this includes also accelerated relative motions.
The equivalence principle was introduced by Einstein as an attempted to at least locally use the concept of special relativity in a gravitational field. It was never meant as way to replace gravity by acceleration on a planetary scale. If you're confined in a small region without any reference to the surrounding you cannot distinguish at a given point in spacetime if you are under the influence of a gravitational field or accelerated by another force because the laws of physics behave in the same manner.
But gravitational fields are not homogeneous, they are gradient fields, therefor the acceleration is not constant and the equivalence principle is not valid within an entire gravitational field.