fossils

Our daughter Caroline is six years old, a fact that is less important to her than the much more exciting fact that she is about to turn seven. The other day Caroline and I were discussing plans for her birthday celebration when she asked, out of nowhere, “If I’m going to be seven, how old is the earth going to be?” “Four and a half billion,” I replied. After being reassured that billion was not, like zillion or cajillion, a made-up word, Caroline wanted to know “how anybody ever figured out such a big birthday number.” “It all started with seashells on mountaintops,” I told her.