Those who hold to the Big Bang Theory and uniformitarianism say that the Big Bang started between 13 and 20 billion years ago. Earth was formed about 4.5 billion years ago. One thing to remember when discussing evolution is that long periods of time are necessary in order for the organisms to have enough time to change from the single-celled to modern man. Another reason some hold to the old-earth view is because they reject the worldwide, catastrophic flood that completely altered earth’s appearance. The geologic column is used to measure the age of the Earth, but this column is only theoretical and based on uniformitarianism.