Lecture 8 Flashcards
Who recognized the immensity of Earth history in the late 1700s?
James Hutton.
What did Sir Charles Lyell demonstrate in the 1800s?
Earth had been through many mountain building episodes.
What was unknown to early scientists about Earth’s age?
They had no way of knowing exactly how old Earth was.
What do rocks record?
Geologic events and changing life forms of the past.
What is a prime goal of geology?
Interpreting Earth’s history based on clues found in rocks.
What discovery was made about Earth’s history?
Earth’s history was discovered to be exceedingly long.
What is the meaning of relative dating in geology?
Rocks are placed in their proper sequence of formation, but it does not provide the age of the rocks, only their order.
What does the Law of Superposition state?
In an undeformed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below it.
Who developed the Law of Superposition?
Priest/geologist Nicolaus Steno in the 17th century.
To what does the Law of Superposition apply?
All surface-deposited materials such as lava flows and ash beds.
What does the Principle of Original Horizontality state?
Layers of sediment are generally deposited in a horizontal position, and flat layers indicate no disturbance.
What does the Principle of Cross-Cutting Relations state?
Younger features (dykes, faults) cut across older features (pre-existing rocks).
What are inclusions in geology?
Fragments of one rock unit enclosed within another. The rock containing the inclusion is younger than the inclusion itself.
What is an unconformity?
A break or gap in the rock record caused by erosion and/or non-deposition of rock units.
When are rocks considered conformable?
When there is no break in the rock record.
What do unconformities represent?
Significant geologic events in Earth’s history.
What is an angular unconformity?
Tilted rocks are overlain by younger, flat-lying rocks.
What is a disconformity?
Strata on either side of the unconformity are parallel.
What is a nonconformity?
Separates older metamorphic or igneous rocks from younger sedimentary strata.
