Complex sentence: Earth is more commonly placed in a Greenhouse state throughout the epochs, and this state takes up approximately 80% of the time that Earth has been around, which makes it a little more difficult to narrow down on direct causes.
Split into simpler sentences: Earth is more commonly placed in a Greenhouse state throughout the epochs, and the Earth has been in this state 80% of the time. This makes it a little more difficult to narrow down on direct causes.