What was robert brown looking at through a microscope when he found evidence of the 1827 scientific concept named in his honor?

Robert Brown was looking at a CELL NUCLEUS through a microscope.

Robert Brown (1773-1858) was a Scottish botanist. Studying the cells of plants, he called the ovals inside those cells the "nucleus" as he watched the interaction of pollen with the cell nucleus. The small, random oscillations of particles in the fluid of the cell are given the name "Brownian motion" based on the sort of fluctuating movement that Brown observed.

i'd say that the moon rock is about 2.2 billion years old.