Together, the 48 contiguous states are comprised of 2,959,064 square miles (which excludes bodies of water).
There are 640 acres in a mile. There are about 4,840 square yards per acre.
To calculate the number of square yards in the United States, we multiply 640 * 4,840 * 2,959,064, which yields 9.17 trillion square yards in the United States.
There are also about 300 million citizens living in the United States. If you had everyone in the U.S. stand next to each other -- let's say they each have their own square yard to stand in -- how much of the contiguous land would be filled?
Answer: about 96 square miles or the size of Plymouth, Massachusetts.
This estimate ignores, of course, the immense land mass known as Alaska as well as Hawaii. Humans would be even less consequential if we took those areas into account.
Each time you fly over the United States, remember how inconsequential humans really are.
Humans represent the metaphorical gnat on an elephant's posterior. And human activities have about as much to do with carbon dioxide, photosynthesis and the rest of the earth's organic processes as Al Gore had to do with the invention of the Internet. Which is to say: none.