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14 Cards in this Set

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  • Back

How old is Earth?

4.6 or 4.7 billion years old. (Universe is 14 billion)

__ is the studying of counting tree rings. We can count backwards from present. How back? Trees in ___ zones (& in some tropical zones) grow __ visible ring per calendrical year. This is because of seasons and periods of ___ contrasted with periods of non-growth. Not all tree species work for ring analyses. Some are better than others. Width of rings, color changes, etc. generally reflect ) ___ affecting growth.

Dendrochronology; 11,000 years*


temperate; one; growth;


climatic conditions;



Large number of measurements using a lot of trees over an area develops regional ring ____ & where the patterns statistically correlate we can extend the chronology spatially and temporally.* Dendrochronology labs are beginning to use chemical analyses of individual rings for correlation and interpretation of ___ variability.

patterns; climatic

How do we count tree rings? It uses a lot of __ matching and statistics to “link” overlaps of different generations of trees and extend the time further back. ____ by Comparing Tree Ring Patterns. We use a LOT of trees and cross correlate across large areas.* HEAVY with statistical analyses.

Using small cutting cores; pattern;


Cross-Dating;


Ice Cores from ___ are ____. Studied with microscopes.Chronologies back ____. Can find Micro samples of gas in bubbles, dust, pollen. Samples of volcanic ash –great regional markers! Samples of nuclear materials (from nuke tests in the 1950’s).

Glaciers; Mother Nature's Ice Box*;


700,000 years*;



___ aka Numerical/Radiometric Ages. Related to radiometric or isotopic dating. Concept of dating is simple, but the terms will make you think it is difficult. Technique is important as are statistical checks and cross checks (both internal and external). It’s fairly complex, precise and uses a lot of ____.___ used to measure the mass of the samples.

Absolute ages; statistics;


Mass Spectrometry;

How Can We Determine Age More Accurately? Thank the ____! ____ are unstable and their nuclei will ___ particles or energy to stabilize. Each radioactive element has a ___–the time it takes for one half of the atoms in a sample to disintegrate forming a ____ product. Neutrons exit nucleus. Some half-lives are fractions of a second while some are as much as 4.5 billion years.

Physicist; radioactive elements;


release; half-life; daughter;



After 1 half-life has passed, half the atoms have changed or emitted energy.After a 2nd half-life has passed half of the remaining atoms have also changed. You can't tell which atom is going to decay. Also, I am a cochina.
Suppose a rock sample has 1/64th of the expected amount of radioactive material.1 -> 1/2 ->1/4 -> 1/8 -> 1/16 -> 1/32 -> 1/64. This means that the sample has been through 6 half-lives. If each half-life is 100,000 years then the rock layer is 600,000 years old. Geologists actually look at __ of parent to daughter product.*

ratios;

__ratios are common for volcanic rocks. ___ has a natural radioactive isotope that has a ½ life of 1.25 billion years. __ is a “noble” gas (boils @ -185.6 C) that escapes (flies away) lava (a liquid). ___ gets stuck in the rock. Curie Point gives us a bonus. Seals the system. “fixes” the magnetic iron. Sample volcanic rock and measure the ratios of each element. When ___ solidifies, that's when the time starts.

K/Ar (potassium/Argon); potassium (solid);


Argon (gas); Potassium; potassium;



REMEMBER Noble gases DO NOT BOND. (aren't party animals)

___ and the quest for the age of the earth. Uranium/Lead relationships. Discovered Earth is ____! Banned leaded gasoline and contributed to the push for the clean air act. Used ___ & concluded the earth is approximately __ to __ billion years old. Why Meteorites?

Claire Patterson*; contaminated with lead*!; Meteorites; 4.4 to 4.7 billion*;


Because operated under the assumption that meteorites are left-over materials from the formation of the solar system, and thus measuring the age of one of these rocks would reveal the age of the Earth.

Uranium/Lead. Check in ___. ___ have a crystalline structure that does not readily accommodate lead. The zircon crystals dislike ___.* Clock starts when the ___ cool below the crystalline “__ point”. “Daughter” products are a bunch of angry lead atoms stuck living with their “parent” atoms. NOT happy. Check seepage through fission-track analyses. Use RATIOS of: Uranium –235 to Lead 207 half-life = 704,000,000 years. Uranium –238 to lead 206 half-life = 4.47 billion years. Check radiogenic decay products against Lead-204 levels in the rock because it is stable. This becomes an internal check. Use LOTS of samples and run LOTS of statistics to check for errors. Develop concordance/discordance isochron charts and plot the calculated ages.

Zircons; zircons; lead;


zircon's; freezing;



When looking at rock layers, strategy is to age-date ___ to bracket non-volcanic rocks and their fossils.

volcanic rocks;