15) “The physical, chemical, and biological laws that operate today have also operated in the geologic past” is a statement of the doctrine of ________________________________.

16) The doctrine of __________________ implies that Earth’s landscape has been developed by worldwide disasters over a short time span.

17) The doctrine of _______________ was put forth by James Hutton in his monumental work Theory of the Earth.

Atoms with the same atomic number but different atomic mass number are called_________.

A(n) ______________ in the rock record represents a long period during which deposition ceased, erosion removed previously formed rocks, and then deposition resumed.

Earth is about _________________ years old.

Which eon of the geologic time scale means “visible life”?

“Most layers of sediments are deposited in a horizontal position” is a statement of the principle of ______.

23) A (n) __________ consists of tilted rocks that are overlain by younger, more flat-lying strata.

A date that pinpoints the time in history when something took place is known as a (n) _______date.