All of the statements regarding the history of life on Earth are true except: Group of answer choices a) The history of planet Earth includes alternations between colder periods ("icehouses") and warmer period ("greenhouses") on the surface of the planet b) The rise of more complex organisms such as eukaryotes has resulted in a reduction of diversity of more "primitive" organisms such as bacteria. c) There have been repeated incidents of mass extinction in the history of the planet in which species diversity has been reduced by 50% or more d) There is more oxygen in the atmosphere today than there was early in Earth history (4 billion years ago)