In your own words, explain the effects of changes in earth's magnetic field over time.

Earth magnetic field may exist due to many causes out of which the most dominating cause is the molten metal inside the core of Earth which will contain large number of ions.

All ions will revolve along with the Earth due to which there exist a current loop due to motion of ions. Now this current may induce magnetic field due to Earth.

Now here the magnetic field of Earth is inclined at some angle with the axis of rotation of Earth. and the North pole of magnet is near the geographic South pole of Earth.

So here by observation it is found that the angle between the magnetic field axis and axis of rotation of Earth is changing with time. This angle is increasing in magnitude.

So there is just change in orientation observed so far due to magnetic field of Earth.