You've already started back peddling, admitting that you're not really up to speed on the finer points of logical reasoning. You would have been better off to admitting the fact and brushing yourself up perhaps. Or maybe it's a lost cause for you at this point. Your understanding is so rudimentary and unsophisticated I could get better results from a couple weeks of tutorship with a middle school student.
I'm not going to go through and contribute to your babbling, so I'll just hit the main points.
1.
Burden of Proof
I should start off by saying that this is probably a much too complex issue for you to apparently wrap your mind around. However, this ought to suffice for your silly request.
The person making a negative claim cannot logically prove nonexistence. And here's why: to know that a X does not exist would require a perfect knowledge of all things (omniscience). To attain this knowledge would require simultaneous access to all parts of the world and beyond (omnipresence). Therefore, to be certain of the claim that X does not exist one would have to possess abilities that are non-existent. Obviously, mankind's limited nature precludes these special abilities. The claim that X does not exist is therefore unjustifiable. As logician Mortimer Adler has pointed out, the attempt to prove a universal negative is a self- defeating proposition.
The Burden of Proof
A common example of correctly applying the burden of proof regarding a negative claim is the distinction between positive and negative atheism. Positive atheists fallaciously assert that the non-existence of God is possible. Meanwhile negative atheists logically assert that absent evidence to demonstrate the existence of God, they will not believe.
Ad Populum
An ad populum argument has NOTHING to do with "the general public" as opposed to a more selective class of individuals. There is no fundamental difference between "everyone agrees it so it must be true," and "most scientists agree so it must be true." In either case, you're appealing to popularity to imply truth value. The fact that you're referring to a group of scientists does not make the ad populum acceptable, nor does it cease to be an ad populum argument. Appeal to authority and ad populum arguments are
not mutually exclusive.
One final note:
It is Argument FROM Authority not Argument TO Authority. I took Latin all through junior high numbnuts

Man, I even throw you a bone and you can't get it right.

If you're such an intelligent Latin scholar you should have correctly corrected me for referring ot argumentum
ad verecundiam. Better luck next time.