To look at evidences of ice ages in what are now
equatorial areas, as Louis Agassiz did in the 19th century,
stimulates a number of possible ideas for mechanisms that could
create such effects. As usual, one key area of disagreement would be
how slowly or quickly these results were achieved--and what
mechanism(s) could create such results, whether slowly or quickly.
Some are extra-terrestrial, such as sun-spot variations
and the shape of the earth's orbit around the sun.
Others are terrestrial, some with clear-cut mechanisms,
such as volcanic ash/gas blocking the sun.
Others present less clear causal possibilities. For
example, a change in the tilt of earth's axis in space, while
keeping its position from pole to pole on the globe so that the
entire globe changes its tilt with reference to the sun.
Or, more radically, a change in the position of
the axis, relative to the globe, but with no change relative to the
sun. Possibly, the entire earth moves to a different position around
Or possibly only the earth's surface moves to a different
position relative to the axis so that the poles remain where they
are, but the real estate under them changes.