The closest to the Sun. The furthest from the Sun. The one that spins most rapidly. Most of the oxygen in the Earth's atmosphere today came from the breakup of the ozone layer. Three of the principal gases, in decreasing order of abundance, in the Earth's atmosphere today are oxygen, argon and nitrogen.
Greenhouse gases are gases which absorb visible light.
Their early atmospheres were probably quite similar in size and composition. Venus must have had a much thicker initial atmosphere. Earth has lost most of its carbon dioxide because of its weaker gravity. Venus has lost most of its oxygen because of its weaker gravity. Venus accumulated less water from the solar nebula.