  The astronomical theory of Milankovitch relates the changes of Earth' past
climate to variations in insolation caused by oscillations of the orbital
parameters. However, this theory has problems to account for some major
observed phenomena of the past few million years. Here, we present an
alternative explanation for these phenomena. It is based on the idea that the
solar system until quite recently contained an additional massive object of
planetary size. This object, called Z, is assumed to have moved on a highly
eccentric orbit bound to the sun. It influenced Earth's climate through a gas
cloud of evaporated material. Calculations show that more than once during the
last 3.2 Myr it even approached the Earth close enough to provoke a significant
shift of the geographic position of the poles. The last of these shifts
terminated Earth's Ice Age epoch about 11.5 kyr ago. The origin and fate of Z
is also discussed.
