Which major gas in today’s atmosphere was introduced by living organisms about 2.7 billion years ago?

Oxygen

Explanation:

Oxygen is the major gas in today’s atmosphere that was introduced by living organisms about 2.7 billion years ago.

answer: 45

explanationyou have to add as well to be it could be

answer:

the water molecules are transferred from the roots to the stem or top parts of the tall tree because of important properties of water which are adhesion, cohesion and capillary action. cohesion is the property of water molecules keeps water molecules in a combined state by sharing of bonds between them at the atomic level. adhesion allows the interaction of water molecules with other substances or substrate. adhesion will cause the attachment of water molecules to the wall of the vessel (xylem) of the plant. capillary action occurs when the adhesive force to the vessel wall is stronger than the cohesive force between water molecules. capillary action mimics the transfer of water from a tube or pipe. in this way water utilizes its property to transfer water from down to top level of the plant.