Consider the following activities: 1. Spreading finely ground basalt rock on farmlands extensively 2. Increasing the alkalinity of oceans by adding lime 3. Capturing carbon dioxide released by various industries and pumping it into abandoned subterranean mines in the form of carbonated waters How many of the above activities are often considered and discussed for carbon capture and sequestration?

1. Activity 1: Spreading finely ground basalt rock on farmlands is a method known as enhanced weathering. Basalt reacts with atmospheric carbon dioxide dissolved in rainwater, converting it into stable carbonate minerals in the soil, thus achieving carbon capture and sequestration. This is an actively discussed approach. 2. Activity 2: Increasing the alkalinity of oceans, for instance by adding lime (calcium hydroxide) or other alkaline substances, enhances the ocean's capacity to absorb and store atmospheric carbon dioxide. This is a form of ocean-based carbon capture and is considered and discussed. 3. Activity 3: Capturing carbon dioxide released by various industries and injecting it into deep geological formations like abandoned subterranean mines or saline aquifers is a well-established method of Carbon Capture and Storage (CCS). Injecting it as carbonated waters is one possible technique for geological sequestration. This is widely considered and discussed. 4. Therefore, all three activities are often considered and discussed for carbon capture and sequestration.