Earth's Climate System:Question 7 Which statement correctly describes how the amount of oxygen in Earth's
atmosphere has changed over time?
Select one:
Large amounts of oxygen were present in the atmosphere both before and after
photosynthesis first evolved.
O
Oxygen started to become scarcer in the atmosphere after photosynthesis first
evolved.
Oxygen started to accumulate in the atmosphere before photosynthesis first
evolved.
Oxygen started to accumulate in the atmosphere after photosynthesis first
evolved
Aw