Origin of Earth's Atmosphere and Oceans
The study of meteorites and material in space suggest the early Earth probably had large quantities of water, organic compounds, and other gases trapped in the accumulating material forming the planet. As a result, as rocks melted large amounts of volcanic outgassing took place. This volcanic outgassing contributed to the atmosphere forming around the planet. Volcanic outgassing from the Earth's interior is still taking place as illustrated by gas emissions from volcanic eruptions such as those on Hawaii or on Iceland where the source of molten material is known to be rising to the surface from the mantle (Figure 1.86).
• Current thought is that large volumes of water vapor and carbon dioxide formed Earth's primitive atmosphere. The atmosphere was also rich in nitrogen, methane, and ammonia.
• Early in Earth history the Earth probably had a thick, hot atmosphere. The surface of the planet was probably hotter than the boiling point of water, so much of the planet's water was trapped as water vapor in the atmosphere.
• Early on, no continents or oceans probably existed (at least no trace of them are preserved from that time), and no evidence of life on Proto-Earth has been discovered.
• Eventually the surface cooled enough for early crust to began to form. With a solid crust and reduced surface temperatures, rainfall could begin to accumulate in depression on the surface. As more and more water was released from the atmosphere oceans began to form.
• By about 4 billion years ago (BYA) the Earth's oceans were essentially in place. Oldest rocks from Canada are of this age.
• Nearly 2 billion years ago, life had advance enough for photosynthesis to take place, gradually consuming the vast reservoirs of carbon dioxide in the atmosphere and dissolved in the oceans, while releasing oxygen to accumulate in the atmosphere (discussed in Chapter 2).