A scientist is observing the decay of a radioactive substance. The amount of the substance remaining is given by the function $A(t)=500(0.95{)}^t$, where $A(t)$ is the amount in grams after $t$ hours, and $t=0$ represents the start of the observation. The model is applicable for $t\ge 0$. If the graph of $y=A(t)$ is drawn in the $ty$-plane, which of the following is the best interpretation of the $y$-intercept of the graph in this context?