There is no scientific experiment in the canonical sense that could confirm it due to ethical concerns. Once it was accepted that aerosol transmission occurs, since it is a much easier form of transmission it's very easy to tag all infections as having occurred through aerosol.
Do all actually occur through aerosol? Some most likely happened like that, others may have been bigger droplets released talking or coughing, others may have been fomites from the droplets...
In my humble opinion, all of those forms occur. Viruses are passive things, they travel in respiratory secretions of any size big enough to contain them. They will lay there doing nothing until they get in contact with a target they can couple to and start replicating. It's better to think of contamination as a probabilistic event modulated by some factors, likely-hood of the event, resiliency of the virus outside of the body under the conditions that lead to the event, etc...
I highly doubt that the virus becomes incapable of infecting in a fomite in a doorknob, elevator button or keyboard. It may be unable to infect after a few hours but that should be plenty of time for an infection to occur.
