In which of these rock diagrams is layer a the oldest

OK it looks like the first diagram is the correct one

Explanation:

Because if you look at it the oldest is always and bottom and the only one with latter a on bottom is the first diagram

In the first diagram

Explanation:

    When talking about the age of a rock, one can speak of absolute age or relative age. Let's see this difference. Relative age does not tell us how many millions of years the rock is. It informs us that this rock is older or younger than another or if it formed before or after a particular geological event.

    By the principle of original horizontality sedimentary formations are originally deposited in the horizontal position. Any dive they present is the result of later bending or tilting. That is, the oldest layer is the one that is underneath all the others.

    No matter how irregular the surface where sediment begins to settle, it will give rise to horizontal or almost horizontal formations. Further efforts of compression or distension may change this situation. There are some exceptions, such as mountain slope deposits and material deposited on large dune flanks; In such cases, careful examination is required to define the original position of the layer.