this event is sometimes called the "cambrian explosion", because of the relatively short time over which this diversity of forms appears. some point to the increase in oxygen that began around 2 billion years ago supporting a higher metabolic rate and allowing the evolution of larger organisms and more complex body structures.

How would the previous sentence be correctly capitalized?
This event is sometimes called the "Cambrian Explosion", because of the relatively short time over which this diversity of forms appears. Some point to the increase in Oxygen that began around 2 billion years ago supporting a higher metabolic rate and allowing the evolution of larger organisms and more complex body structures.