mostly classic movies: what good is sitting/alone in your room come! hear the music play!?

Questions

before the 1800's there were no separately designed ---------- for right and left feet?

czar ---------- banished soldiers to siberia for marching out of step?

czar paul i banished soldiers to ---------- for marching out of step?

during the ---------- period, about 500 million years ago, a day was only 20.6 hours long?

during the cambrian period, about ---------- years ago, a day was only 20.6 hours long?