The greenhouse gas carbon dioxide to
a. deflect harmful radiation from space.
b. increase precipitation in arid areas.
c. form clouds in the atmosphere.
d. maintain warmth near earth’s surface

The greenhouse gas carbon dioxide helps to D. Maintain warmth near Earth's Surface, but if this gas is created of what it's necessary, it could create prejudicial damages

As of 2019 7.7 billion

They contributed many things, but here are some examples:

1) democracy - democracy as a political system was first implemented in ancient athens
2) some advances in mathematics - such as the pythagoras' law
3) the script - the roman script was adopted from ancient greek.