Evolutionary Timeline

n = 100;
bil = 10^9; years =
 Reverse[Map[Reverse,
   Table[n ( i - 1) + j, {i, 3.8 n}, {j, n}]*100000]];
cols = Table[ColorData["DarkBands"][i/11], {i, 11}];
(* each point is x years ago *)(* What colour, given y years ago? *)
colouring1[y_] := If[y <= 200000, Red (* humans*),
   If[y <= 2.5 * 10^6, Blue(* Homos*),
    If[y <= 65*10^6, cols[[3]] (* dinosaurs dead*),
     If[y <= 200 *10^6, cols[[4]] (* mammals*),
      If[y <= 300*10^6, cols[[5]] (* reptiles*),
       If[y <= 550 *10^6, cols[[6]] (* complex animals*),
        If[y <= 600*10^6, cols[[7]] (* simple animals *),
         If[y <= 10^9, cols[[8]] (* multicellular life *),
          If[y <= 2 *10^9, cols[[9]] (* complex cells*),
           If[y <= 3*10^9, cols[[10]] (* photosynthesis*),
            cols[[11]] (* simple cells*)
            ]
           ]
          ]
         ]
        ]
       ]
      ]
     ]
    ]
   ];
colouring[y_] := Module[{c = colouring1[y]}, {c[[1]], c[[2]], c[[3]]}];
image = Map[colouring, years, {2}];
Image[image]