Describe the motion of the blocks before and after they are knocked down. Also describe the interactions of the blocks with other objects as they are knocked down and fall.

The motion is described by the Newton's third law.

According to  the first statement, it states that there is equal and opposite reaction. That is the cause and its effect.When the blocks are knocked down which means there is transfer of energy and momentum in the two bodyThese are described as the conservation of the energy and momentum before and after it remain same.In the second statement, there is fall of blocks which shows that here the conservation of momentum does not take place.Because the first block has more energy than the second block.

Because the dept in the ocean

Not what goes around on earth but the universe too.