You are right
As you mentioned, science is ever dynamic and ever changing. What was considered fundamental today may be proven to be horribly mistaken tomorrow. That is the beauty of Science, its ability to not just accept things as a given, but challenge why, how and what they are, moving closer and closer to a better, but never perfect understanding of our world.
As for no unquestioned authorities in science, you have again hit the nail on the head. There are professionals and experts which we generally look up to as leading figures who mostly get it right, but they do not control scientific thought. Anyone can challenge them on what they say, and if they are right then they are celebrated for helping to prove understanding.
On the other hand, no one is discouraged from entering science. On the contrary, we need more people! However, much as free thought is promoted among scientists, a rigorous proofing of material is needed to make sure complete nonsense doesn't get through. Luckily, science ha that, with its peer-review system. Although not perfect, it ensures that only material that is logical and has evidence for its claims can come through to mainstream science. This means that even if you write an article about the sun being made if ice-cream, if you can prove what you say, it will be accepted.
That is my comment on science, and I hope it helped!