I’m a man and wear a tasteful hoop earring on one ear. Is it appropriate for me to wear this on my first interview?

What you are wearing and your overall grooming are part of your “package” and can contribute to your making a favorable or unfavorable impression.  Keep in mind that there is no such thing as neutral clothing – everything you wear says something about you.
When choosing your interview wardrobe, it is better to over dress than under dress.  When in doubt, error on the side of conservatism.  A smart business suit is appropriate in almost any interview situation.  Many interviewers indicate they think a person dressed in a business suit is more serious about the position than someone who is dressed more casually.  At a minimum, you should appear clean and neat.  Your shoes should be polished and your clothes should be pressed and unwrinkled.   When buying new clothing for your interview wardrobe, concentrate on quality versus quantity.  One well-made suit will last longer and give you a better image than several cheaper versions.  Don’t neglect tailoring.  Make sure that your interview clothes fit you well and are neither too large nor too small. Also, with the exception of conservative single ear piercing for women, no other body piercing should be visible during an interview.