On planet zorba, a solar blast has melted the ice caps on its equator. 8 years…

On planet zorba, a solar blast has melted the ice caps on its equator. 8 years after the ice melts, tiny plantoids called. echina start growing on the rocks. echina grows in the form of a circle and the relationship between the diameter of this circle and the age of echina is given by the formula d = 2 x root of t - 8 for t >= 8 where d represents the diameter in mm and t the number of years since the solar blast. Jagan recorded the radius of some echina at a particular spot as 4 mm. How many years back did the solar blast occur?