The correct answers to this open question are the following.
My speculation about the purposes of the South American Nasca drawings and the Serpent Mounds of North America are the following.
The Nazca drawings are located in a desertic area in Peru. They are a series of lines and animal figures that only can be devised by air. These long lines look like landing tracks such as the ones that are built in airports. So one of the theories that Nazca was a landing place for ET's starships. The animal figures meaning are still a mystery.
On the other hand, the Great Serpent Mound is located in southwest Ohio, United States. It is a long mound with the form of a large serpent. People give it mystical meanings due to the fact that the head of the mount or"serpent" aligns with the sunset in the summer solstice. Archeologists debate about the meaning of the mount: some say it was a kind of celestial compass. Others think there were totems over the mound.
The force of gravity acting on an object due to its mass. An object's weight is directed down, toward the center of the gravitating body; like the Earth or moon, for example.
