Do I have to attack players gathering in rare earth field to get a chance to gather?

No, you can just go into s vacant spot and start gathering. There is a rare earth symbol with a magnifying glass that will find an open spot for you, but if all the spots are taken, then there is a cool down period before you can try again. The cool down is possibly 5 minutes....I don't know, but thought that was mentioned in something else I read about it.