Then green plants evolved in the oceans and they began to add oxygen to the atmosphere as a waste gas.
(green plants; evolved; L:in the oceans; T:Then) (they; began; to add oxygen to the atmosphere as a waste gas) Context(they began,List([44, 54))):(they; began to add; oxygen; to the atmosphere)
they began,List([44, 54))
green plants they they
evolved began began to add
L:in the oceans T:Then
to add oxygen to the atmosphere as a waste gas
oxygen to the atmosphere