Video Transcript
The image below shows a section of
sedimentary rock. Which label corresponds to the
oldest layer of the rock?
Sedimentary rocks are rocks formed
from the deposition, accumulation, and solidification of small mineral or organic
particles. During the formation of sedimentary
rocks, small bits of rock, sediment, or sand are deposited into a layer. Over time, more and more layers of
sediment or sand are deposited on one another. As the layers increase, the
pressure on the bottom layer increases. The increased pressure forces the
sediment in the bottom layer to compact together. The increased pressure also removes
water from the bottom layer. This cements the sediment together,
forming the first layer of sedimentary rock.
Compaction and cementation can
occur with each successive layer, building up the layers of sedimentary rock from
the bottom up. As the bottommost layer solidifies
first, this layer represents the oldest layer of rock. As the layers of sedimentary rock
solidify from the bottom up, the top most layers will be newer than the bottom.
In this question, we want to know
which label in the diagram corresponds to the oldest layer of rock. The bottommost layer, labeled E,
will have solidified before the layers above it. Therefore, the label that
corresponds to the oldest layer of the rock is E.
