InstructorsStudentsReviewersAuthorsBooksellers Contact Us
image
  DisciplineHome
 
 
 
 
 
 
 
 ResourcesHome
 Bookstore
Student Resource Center
GeologyLink
Glossary
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

U


unconformity
A boundary separating two or more rocks of markedly different ages, marking a gap in the geologic record.
uniformitarianism
The hypothesis that current geologic processes, such as the slow erosion of a coast under the impact of waves, have been occurring in a similar manner throughout the Earth's history and that these processes can account for past geologic events. See also catastrophism.
upwarped mountain
A mountain consisting of a broad area of the Earth's crust that has moved gently upward without much apparent deformation, and usually containing sedimentary, igneous, and metamorphic rocks.
uranium-thorium-lead dating
A form of isotope dating that relies on the extremely long half-life of radioactive isotopes of uranium, which decay into isotopes of lead, to determine the age of rocks in which uranium and lead are present.

Credits


BORDER=0
Site Map I Partners I Press Releases I Company Home I Contact Us
Copyright Houghton Mifflin Company. All Rights Reserved.
Terms and Conditions of Use, Privacy Statement, and Trademark Information
BORDER="0"