The differences between the young Earth interpretation of Genesis and modern scientific theories such as Big Bang, abiogenesis, and common descent are significant. The young Earth interpretation says that everything in the universe and on Earth was created in six 24-hour days, estimated to have occurred some 6,000 years ago. Modern scientific observations, however, put the age of the universe at 13.8 billion years and the Earth at 4.5 billion years, with various forms of life, including humans, being formed gradually over time.