Does the circumference of the earth remain constant?

Answer 1

Essentially, yes. The earth accumulates cosmic dust, meteorites and the occasional comet, but not at a rate significant enough to appreciably change the earth's circumference. The sinking of heavy rock, such as caused by the recent 8.8 magnitude earthquake in Chile also does not measureably change the earth's circumference. Some scientists estimated earth's rotational velocity may have accelerated as much as a millionth of a second per day from that earthquake, however.

The motion of the continental plates about earth's surface does not appreciably affect earth's circumference either. These plates move about on a half billion year cycle known as the Wilson Cycle.

Answer 2

No, the circumference of the Earth actually changes slightly over time due to factors such as tectonic plate movement, sea level changes, and gravitational forces. Overall, the changes are minimal and not easily noticeable on a human timescale.