Geologic Time

GEL 130 QR- Reading Guide

Complete and use this guide as reference for Lecture Quiz 6

Geologic Time (Chapter 18)

· Section 18.1

1. What is the difference between numerical and relative age?

2. Relative Dating use basic logic principles that help to place events in chronological order from oldest (what happened first?) to youngest (what is the youngest event or rock?).

Complete the flow chart below with the principles of relative dating:

Relative dating: Which is older? Which is younger?	Uniformitarianism	“The present is the key to the past” (see chapter 1)
	Superposition	“ In a sequence of sedimentary rocks (layers): the layers at the bottom are older , the one on top are younger” Fig. 18.2	( OLDER YOUNGER )
	Original Horizontality
	Lateral continuity
	Cross cutting Relationships
	Inclusions

Unconformities: Are you missing something? Unconformities are surfaces that represent gaps in the geologic record, they form wherever rocks were not deposited for a time or else layers were removed by erosion.

Watch video: Unconformities: finding missing time

· Why are unconformities surfaces important?

3. There are three kinds of unconformities, Carefully read how each type of unconformity forms and identify them in textbook figs 18.8-12. Summarize how each unconformity forms:

· Disconformity:

· Angular Unconformity

· Nonconformity

· Fossils:

4. What are some of the most common forms of fossil preservation?

5. What is an index fossil?

Absolute dating: how to determine numerical ages of rocks and geologic events? (read section 18.4)

· Watch video: Numerical Time Numerical time:

6. Review of atom structure ( check chapter 3):

· Atoms of the same element have the same number of protons (a.k.a atomic number).

· For example the element Carbon has 12 protons:12C;

· The element Oxygen has 8 protons: 8O

However within atoms of the same element there are atoms with different atomic mass or different number of protons:

 

These atoms are called: isotopes: atoms of the same element, with the same number of protons but different number of neutrons.

Some isotopes are unstable atoms (like Maria), what means that over time these atoms will transform into something else: the process is called radioactive decay.

7. Define: parent isotope , daughter isotope and half life :

There are three different types of radioactive decay, in general:

( New element (daughter) (parent) ) ( Radiation (energy) ) ( Unstable Isotope (parent) )

( + )

8. What is radiometric dating ? How is radioactive decay used to determine the age of a rock?

For each isotope there is a particular rate of decay, in other words: each isotope disintegrates a different speed. Another way of expressing the rate of radioactive decay is_____________________.

9. Check Fig. 18.21 from textbook and answer:

· When 1 half life has elapsed since the formation of a rock, there will be 505 of the parent isotope remaining and ____ % of the new daughter isotope

· After 3 half lives there is ______ % of parent isotope and ____% of new daughter isotope.

Also watch: how does radiocarbon dating work?

Note: In class we will go with more depth into this concept, bring your notes.