Or commercial fish farming, is one way in which new species enter freshwater and marine ecosystems.
a. aquaculture,
b. biodiversity,
c. conservation,
d. pollution,

which

what is a measurement of the earth’s history divided into time periods?

> fossil record <

sedimentary rock

> geologic time scale <

radioactive elements

the law of original horizontality explains:   why rocks appear in layers. correct answer: b the law suggests that all rock layers are originally laid down (deposited) horizontally and can later be deformed.   the principle is used by geologists to make assumptions about the relative ages of sedimentary rocks.