Indentifiyng species is the answer
[ Equilibrium / Diffusion ] is the simplest type of passive transport. 7. The diffusion of water through a selectively permeable membrane is called [ osmosis / diffusion ].
Half-life = time in which half of material is lost
1/4 = 1/2 x 1/2 so 2 half lives have gone by if only 1/4 of it is left.
age of rock = 2 x half life = 2x1.3 = 2.6 billion years.