Ice ages may have occurred from worldwide cooling.  The cooling took place for tens of millions of years before the beginning of the molding of glaciers.  That is one of the things that scientists think could have contributed to the cause of ice ages, but there are still other possibilities.

    Another possible cause of the ice ages is reduction in the amount of CO2 in the atmosphere.  CO2, which is carbon dioxide, is an important Greenhouse gas.  A decrease in the amount of CO2 in the atmosphere could have led to global cooling.  Still scientists are not sure if this is the cause of the ice ages.

    Some scientists believe the change in incoming solar radiation may have contributed to the devlopment of the ice ages. Earth's orbit is always changing through time.  There are important parameters that vary, including the eccentricity of the orbit around the sun, the tilt of the Earth's orbit, and the direction the north pole points.  The variation in these three factors change the amount of incoming solar radiation.  Still, the cause of ice ages could be something totally different.