1907 - Bertram Boltwood proposes that the amount of lead in uranium and thorium ores might be used to determine the Earth's age and crudely dates some rocks to have ages between 410--2200 million years
1911 - Arthur Holmes uses radioactivity to date rocks, the oldest being 1.6 billion years old
1960 - Harry Hess proposes that new sea floor might be created at mid-ocean rifts and destroyed at deep sea trenches
1963 - F.J. Vine and D.H. Matthews explain the stripes of magnetized rocks with alternating magnetic polarities running parallel to mid- ocean ridges as due to sea floor spreading and the periodic geomagnetic field reversals
Geology (from Greek γη- (ge-, "the earth") and λογος (logos, "word", "reason")) is the science and study of the Earth, its composition, structure, physical properties, history, and the processes that shape it.
The word "geology" was first used by Jean-André Deluc in the year 1778 and introduced as a fixed term by Horace-Bénédict de Saussure in the year 1779.
In geology, when an igneous intrusion cuts across a formation of sedimentary rock, it can be determined that the igneous intrusion is younger than the sedimentary rock.
Geology (from Greek γη- (ge-, "the earth") and λογος (logos, "science")) is the science and study of the earth, its history, and the processes that shape it.
Geology is also sometimes used about similar studies of other bodies of the solar system.
Subdisciplines within geology proper include structural geology, sedimentology and stratigraphy, mineralogy (study of minerals), petrology (study of rocks), geomorphology (study of landforms), seismology (also a field in geophysics) and volcanology (the study of volcanic activity).
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