When I was a grad student (and cars were called horses, and planes were used to shape wood…), I had a chemistry student housemate. He said that when students wrote papers in his department, the professor got first authorship even if he had no direct input into actually doing the work. I didn’t believe him. In every (geology) institution that I’ve worked in, the first author is the person who actually writes the words, and is usually also the person who performs the experiments (especially if they are a student). Supervisors who had significant input into drawing conclusions from the results got last authorship; professors who didn’t care were lucky to make the acknowledgements, usually as a funding source.