Which of these changes Earth’s climate mainly over time spans of millions of years?(1 point)
• plate tectonics
• human interactions
• ocean currents
• volcanic eruption

Which of the following is true of the surface water and deep water of the ocean? (1 point)
• There is little vertical mixing between layers because currents only flow sideways.
• There is constant vertical mixing between layers because the warm water is atop the colder water.
• There is constant vertical mixing as freshwater evaporates and the salty surface water that remains sinks.
• There is little vertical mixing between layers because the warm water is atop the colder water.