What must be true about the age of rock layers in which leaves appear?

If leaves appear in certain rock layers, those layers must be younger than the age of the leaves themselves, as the leaves must have existed before they were buried in sediment. Additionally, the presence of leaves suggests that the environment at that time was conducive to plant life, indicating that the rock layers formed during a period when terrestrial vegetation was present. Thus, the age of the rock layers containing the leaves reflects a time when the conditions for leaf formation were met.