How do the oceans contribute to the Earth's oxygen supply? They absorb all oxygen from the atmosphere. They only contribute through coral reef systems They have no effect on oxygen levels. They contribute through photosynthesis by marine plants and algae

## Step 1<br />The question asks about the role of oceans in contributing to the Earth's oxygen supply. The options provided are:<br />- They absorb all oxygen from the atmosphere.<br />- They only contribute through coral reef systems.<br />- They have no effect on oxygen levels.<br />- They contribute through photosynthesis by marine plants and algae.<br /><br />## Step 2<br />The first option, "They absorb all oxygen from the atmosphere," is incorrect. While oceans do absorb oxygen, they do not absorb all of it. There is still a significant amount of oxygen left in the atmosphere.<br /><br />## Step 3<br />The second option, "They only contribute through coral reef systems," is also incorrect. While coral reefs do contribute to oxygen production, they are not the only source of oxygen in the oceans.<br /><br />## Step 4<br />The third option, "They have no effect on oxygen levels," is incorrect. Oceans play a significant role in oxygen production through photosynthesis by marine plants and algae.<br /><br />## Step 5<br />The fourth option, "They contribute through photosynthesis by marine plants and algae," is correct. Marine plants and algae, such as phytoplankton, are primary producers in the ocean. They use sunlight to convert carbon dioxide and water into glucose and oxygen through photosynthesis. This process contributes significantly to the Earth's oxygen supply.