how sure are scientists that life came from bacteria, how do they test it and can they say it's Is pretty much fact?
I know that all life forms have evolved, and natural selection is a theory of how organisms evolved, but does the science community think natural selection is fact? And do you think it will ever be disproved?


There's plenty of evidence for natural selection so it's unlikely in the forseeable future that it'll be disproved.

This article is a good place to start your research:

http://en.wikipedia.org/wiki/Evolution# … ry_of_life

No, it isn't true that we evolved from bacteria.

The term "bacteria" is quite specific, just like "animal". While the current thinking is that all life evolved from a single-celled ancestor which may be superficially similar to bacteria, what we call bacteria today is the product of ~4 billion years of evolution from that single celled ancestor. So, we certainly did not evolve "from bacteria". Instead, bacteria (which is actually more accurately divided into two completely separate groups; archeobacteria and eubacteria) and us have a common ancestor which was probably single-celled. We can expect that the common ancestor is as different from us humans as it is from any given bacterium alive today.

Common decent is heavily implied by the common biological chemicals we use, namely DNA, RNA, lipids, sugars and amino acids. Also, we have conserved genes in common, in particular those around protein production and other basic molecular biology (e.g. the ribosome). This basic machinery is so much the same that human genes can be utilised by bacteria under the right circumstances, and the other way around can work too.

Having said all that, we don't know 100% that this view is the correct one, but all of the evidence points in that direction and at this point it would be very surprising to say the least if it were shown to be false.