Re: The moon-earth barycenter at sea level would cause what change?

There is no relationship between the location of the center of gravity of two bodies (called the barycenter when they orbit each other) and the tides that either experience. The tidal force across an object is high when that body is fairly large compared to the distance between it and the other body. For example, the Moon is only 30 Earth diameters away. The Sun is 11,740 Earth diameters away, and this larger value explains why solar tides are smaller than lunar tides, despite the much greater mass of the Sun.

Looking at the Earth-Moon system, consider two ways we could bring the barycenter to the Earth's surface (it is currently about 75% of the way between the center and the surface).

First, we could increase the distance between the two bodies. As the Moon moves farther out, the barycenter gets closer to sea level. Eventually the barycenter is in space between the Earth and Moon. The farther away the Moon, the smaller the tides on Earth. The tides decrease smoothly as the lunar distance increases, and are proportional to the inverse cube of distance. When the lunar distance is increased about 40%, the barycenter will be at the surface of the Earth and tides from the Moon will be reduced to about 30% of their present level.

Second, we could increase the mass of the Moon. As the mass increases, the barycenter moves outward, and will eventually be at sea level. Continuing to increase the lunar mass will move the barycenter into space. As the mass increases, the tidal forces at the Earth will increase linearly. When the mass of the Moon is increased about 40%, the barycenter will be at the surface of the Earth and tides from the Moon will be increased about 40% from their present level.

In both of these cases the tides either increase or decrease smoothly, with no sudden change when the barycenter coincides with the surface of the Earth. If you are interested in exploring the math behind tides, start with the Wikipedia article at en.wikipedia.org/wiki/Tidal_force.

It has been speculated that our massive, close moon helped make life on Earth possible by creating large intertidal zones with a dynamic environment. I can't think of any reason that life wouldn't be possible on a planet that experienced much higher tides, regardless of the location of the barycenter.