What causes the youngest layers to be on top

When the sediment move and they are being settled somewhere, it means they are being deposited.

After a long period of time, there is a formation of layers of sediments on the top of each other. The weight of the top layer of sediment presses the lower layer and settle down it to the bottom layer, which results in the formation of sedimentary rock.

The oldest layer is on the bottom of the layer and the youngest one would be on the top layer because sediments include living organism, which often contains a fossil fuel.

the answer is trees if i'm not mistaken

1. efficient use of space

2. elimination of groundwater contamination

3. energy generation

4. lower carbon footprint