Final answer:
Ice ages in the past were primarily caused by changes in the Earth's axial tilt and variations in sunlight due to the gravitational effects of other planets. There is also evidence of a period called snowball Earth where the entire ocean froze over.
Step-by-step explanation:
Ice ages in the past were primarily caused by changes in the tilt of Earth's rotational axis, which were produced by the gravitational effects of other planets. These changes in the Earth's axial tilt resulted in variations in the amount and distribution of sunlight reaching the Earth's surface, leading to cooling and the accumulation of ice. There is also evidence of a period called snowball Earth, where the entire ocean froze over about a billion years ago.