C- The Earth is 4.5 – 4.6 billion years old. At first, it contained large amounts of H and He gases. Most of these gases escaped into space.
Timeline of the Earth's Atmosphere
Joules Sheridan and Elaina Ramos
Our Timeline
E- Approximately 3.5 – 4 b.y.a. the Earth began to cool down and water vapor condensed into liquid water. Liquid water began to collect on the earth’s surface in lakes and oceans. The amount of water vapor in the atmosphere decreased. The atmosphere was about 70% carbon dioxide gas and 30% nitrogen gas.
H- A lot of carbon dioxide gas was absorbed by the oceans by about 3.5 billion years ago. This reduced the amount of carbon dioxide in the atmosphere to about 20%.
F- About a billion years ago, some living organisms began to use energy from sunlight to turn carbon dioxide gas and water into sugar and oxygen gas (a process called photosynthesis). The amount of carbon dioxide gas was about 15%, but it began to decrease. The amount of oxygen gas was less than 1%, but it began to grown because of the oxygen produced by living organisms.
I- High in the atmosphere, some oxygen (O2) molecules absorbed energy from the Sun's ultraviolet (UV) rays and split to form single oxygen atoms. These atoms combining with remaining oxygen (O2) to form ozone (O3) molecules, which are very effective at absorbing UV rays. The thin layer of ozone that surrounds Earth acts as a shield, protecting the planet from irradiation by UV light. The shield is believed to have been in existence 600 million years ago.
G- The first land plants appeared on the earth about 400-500 million years ago. The plants took in carbon dioxide and produced oxygen gas through photosynthesis. The amount of oxygen gas in the atmosphere continued to increase, approaching 21%.
B- For the first 500 m.y. the Earth was very hot, and there were many erupting volcanoes releasing gases. These gases water vapor, carbon dioxide, nitrogen, and sulfur dioxide created the atmosphere. There was no oxygen gas in this atmosphere.
A- The modern atmosphere is 78% nitrogen gas, 21% oxygen gas, and less than 1% carbon dioxide gas. This was formed approximately 290 m.y.a.
D- The amount of carbon dioxide gas in the modern atmosphere is less than 1%, but recent measurements taken at a Hawaiian laboratory show that it is slowly increasing. In 1959, the percentage of carbon dioxide in the atmosphere was 0.0316%. In 2004, it was 0.0377%. This is a 19% increase in the amount of carbon dioxide in the atmosphere. The increased burning of fossil fuels by greater numbers of people is one reason for this change.