There was something that the God didn't like, so he decided to wipe everything and start the life over again. However, this task is on you now, so you have to use various God's tools to get rid of all cave people around.
The God's will should be done and you are the one to do this. He is angry, because of the deeds of cave people and other creatures of the Earth, so he decides to wipe everything and start a new era. Use all available resources and strike these cave people with the power of nature. Make sure nobody survives this!