What is the most rare element in periodic table
Well, the first question to answer would be: where?  The rarest element in the universe? the sun? in meteorites? on earth? in the ocean? in humans?  We can tap in to the curated datasets provided by Mathematica to get the answer:

Elements up to atomic number 98 have been found in trace quantities; however, the dataset does not contain any information about the trans uranium elements which were once thought to be synthetic.
Here's a plot of abundance as a function of atomic number:

We can see that the elements beyond about Z = 82 (lead) have a marked decrease in abundance, and this is consistent with all of the elements with atomic number above 82 being radioactive.
Where do we come from?
We can compare the elemental abundance of these individual &quot;spaces&quot; to speculate on where humans come from.  Below are plots showing the correlation of the elemental abundances.  The plot labels give the best fit equation:

The best slope is observed when comparing our abundance to that of the Earth's crust; however it does appear as if the scatter is smallest for the Us vs. the Ocean plot.