What two processes led to the reduction of carbon dioxide in the atmosphere before life on Earth?

The correct answer highlights two significant processes that contributed to the reduction of carbon dioxide in the atmosphere prior to the emergence of life on Earth.

Firstly, carbon dioxide dissolving in oceans plays a crucial role. When carbon dioxide enters the oceans, it can react with water to form carbonic acid, which subsequently leads to the formation of bicarbonate and carbonate ions. These compounds can then precipitate out of the water under certain conditions, forming sedimentary rocks such as limestone. This geological process effectively removes carbon dioxide from the atmosphere, as carbon is locked away in solid mineral formations for long periods.

In addition, as carbonates precipitate, they sequester carbon in a solid state in ocean sediments. This process not only decreases the concentration of carbon dioxide in the atmosphere but also contributes to the long-term carbon cycle on Earth, influencing climate and atmospheric composition through geological timescales.

While other choices involve mechanisms related to carbon dioxide, such as plant absorption or icy formations, they are either not applicable to the pre-life conditions on Earth or do not accurately reflect the significant geological processes that reduced atmospheric carbon dioxide during that time.