As the second most abundant greenhouse gas in our atmosphere (after water vapor), carbon dioxide (CO2) has become a direct proxy for measuring climate change. Its levels have varied widely over the course of the Earth’s 4.54 billion year history, partly driving swings in our planet’s average temperature.
The History of CO2
Scientific consensus today describes our atmosphere’s evolution in three stages. Around the time of Earth’s formation, our solar system was dense with helium and hydrogen which bounced around the Earth’s surface at extremely high temperatures. These molecules eventually escaped into space and were replaced by our second atmosphere: volcanic emissions. Eruptions dispersed water steam, CO2, and ammonia (one nitrogen and three hydrogens), forming a gassy blanket above and early water bodies below. CO2 slowly dissolved into the shallow ocean and allowed cyanobacteria to perform oxygen-emitting photosynthesis. This oxygen eventually accumulated until the atmospheric composition changed enough to kill off most micro-organisms present at the time, about 2.4 billion years ago.
CO2 and Past Climates
As a point of reference, pre-industrial CO2 levels were around 280 parts per million (ppm) and today, we stand near 420 ppm.
Continue reading at EARTH * ORG