Greetings.
Recently I have been working on a project for a class. Within the project I am attempting to display multiple circles constantly increasing in size as a For loop progresses. I have no problem increasing the size of the circles, nor displaying the circles, but the circles are constantly being over written by the next circle. I have been attempting to find a way to combine all of the circles into one graph, and also combine each circle into it's own graph (for individual use). This is the code I have written so far (there will also be an attatched copy).
xSt[] = 0; (* x starting position *)
ySt[] = 0; (*y starting position *)
years = 0; (* The years that pass *)
endTime = 100; (* Amount of years until the end of time *)
probLife = 0; (* The probability that life will sprout up *)
nLife = 0; (* Amount of Circles of Life; and designation number *)
circleLife[] = 0; (* Circle of Life *)
rMulti = 0 ; (* Growth multiplier *)
rBase = 0; (* Base growth rate *)
rGrowth[] = 0; (* Rate of Growth for each CoL *)
orgGrowth[] =
 0; (* Used to keep track of original growth rate assigned to \
specific life form *)
ContourPlot[x y, {x, -1, 1}, {y, -1, 1},
PlotRange -> {{-100, 100}, {-100, 100}},
PlotLabel -> Dynamic["Year = " <> ToString[years]],
Epilog -> Dynamic[plot[[1]]]]
For[years = 1, years < endTime,
 probLife = RandomInteger[{1, 10}];
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 (* The following If function checks if there are any circles of \
life and if there is, begins updating them,
 as if the life form is expanding radially *)
 If[nLife > 0,
  For[n = 1, n <= nLife,
   n++,
   rGrowth[n] = rGrowth[n] + orgGrowth[n];
   plot =
    ContourPlot[((a - xSt[n])^2 + (b - ySt[n])^2 ==
       rGrowth[n]^2), {a, -100 \[Pi], 100 \[Pi]}, {b, -100 \[Pi],
      100 \[Pi]},
     PlotRange -> {{-100, 100}, {-100, 100}}];
   (* Pause[0.1] *)](* End For n *)
  ]; (* End If nLife *)
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 (* The following If function checks if the probability of life \
forming is true and if so creates a new form of life at a random \
point on the plot and the size and growth rate of that life form *)
 If[probLife == 1,
  {nLife = nLife + 1;
    xSt[nLife] = RandomReal[{-100, 100}];
    ySt[nLife] = RandomReal[{-100, 100}];
    rMulti = RandomReal[{.01, .1}];
    rBase = RandomReal[{1, 10}];
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    rGrowth[nLife] = (rMulti rBase);
    orgGrowth[nLife] = (rMulti rBase);
    plot =
     ContourPlot[((a - xSt[nLife])^2 + (b - ySt[nLife])^2 ==
        rGrowth[nLife]^2), {a, -100 \[Pi],
       100 \[Pi]}, {b, -100 \[Pi], 100 \[Pi]},
      PlotRange -> {{-100, 100}, {-100, 100}}]};
  ]; probLife = 0;(* End If probLife *)
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 (* Pause[0.1]; *)
 years++;
 ] ;(* End For years*)
Also, while attempting a variety of different methods and approaches, I receive this error message
"An improperly formatted option head (Graphics) was encountered while reading a Graphics. The head of the option must be Rule or RuleDelayed."
But I do not know exactly what it means, and my searches for an answer to this online has been fruitless.
Please help me Mathematica Community, you're my ony hope.
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