Final answer:
Ice ages on Earth are primarily caused by changes in the tilt of Earth's rotational axis and may be ended by factors such as increased solar activity, changes in Earth's orbit, and volcanic activity leading to warmer temperatures.
Step-by-step explanation:
The Earth has experienced several ice ages, which are periods characterized by extensive glaciation across the planet. These ice ages are primarily caused by changes in the tilt of Earth's rotational axis due to the gravitational pull of other planets. Moreover, there have been times, possibly about a billion years ago, when the entire ocean may have frozen over in an event referred to as 'snowball Earth.'
The release of Earth from a frozen period or ice age can occur due to a variety of factors including increased solar activity, shifts in Earth's orbit, volcanic eruptions, and changes in atmospheric composition. Particularly, the last ice age ended about 10,000 years ago, when the Earth entered an inter-glacial period with warmer temperatures that effectively released the large ice sheets that covered the Northern Hemisphere.