Question | Answer |
measured by man directly | Time |
heart beats | Time |
pendulum swings | Time |
atomic cyclic vibrations | Time |
redefined in 1967 | Time |
9,192,631,770 vibration cycles of a cesium atom | second |
rotation of the Earth | day |
lengthening 1 sec/year | variable |
1.5 Ga day | 11 hours |
20 hours - based on daily growth rings | 400 Ma day |
moon around the Earth | month |
Earth around the Sun | year |
changes in growth cycles | seasons |
because the Earth is inclined on its axis | seasons |
produces growth rings in plants | seasons |
bristle cone pines in the southwest U.S. | example of growth rings |
oldest known trees | >5000 yrs. |
used to calibrate 14C dates | trees |
produces growth rings in animals | seasons |
tidal control | claims |
fish scales | growth rings |
scallop growth bump | growth rings |
high erosion, low erosion cycles | varves |
back to ~15,000 years b.p. | glacial |
more cycles in the past indicates shorter days in the past | growth rings |
salt in the ocean | major argument on Earth age |
1899,Irish physicist estimated - Earth age ~99.4 million years old | Joly |
ocean thought initially salty | refuted |
cooling rate of the Earth | major argument on Earth age |
middle 1860s -a physicist | Lord Kelvin |
time necessary to cool from a liquid | Lord Kelvin |
Earth age 10-20 million | Lord Kelvin |
radioactive heating discovered 1896 | Becquerel |
sediment deposition rate since fossils appeared | major argument on Earth age |
total thickness versus rate of accumulation137,195 0.305m/1000 years | sediment deposition rate |
>450 million years old | fossil bearing rocks |
age estimates based on radioactive decay estimates | major argument on Earth age |
spontaneous breakup of the atomic nuclei of certain unstable substances | radioactivity |
discovered in 1896 by Becquerel - French physicist | radioactivity |
isolated energy producers from Uranium | Curies |
1898 - Curies discovered Radium, atomic number 88 | Radium |
radioactive disintegration | decay |
nuclei of helium atoms | alpha particles |
2 protons | helium |
2 neutrons | helium |
electrons | beta particles |
electromagnetic radiation | (gamma) rays |
- like light but with a very short wavelength | gamma rays |
unstable elements | radioactive isotopes |
spontaneous decay of individual particles is unpredictable | radioactive isotopes |
decay of half of the atoms is statistically predictable | radioactive isotopes |
(t1/2) - time it takes for half of the atoms of an isotope to disintegrate | half-life |
(ln 2)/l; where l = decay constant | t1/2 |
varies from fractions of a second to billions of years | t1/2 |
a constant relating the instant rate of radioactive decay of a radioactive species to the | decay constant |
naturally -in our atmosphere (14C) | cosmic radiation |
in the laboratory | cosmic radiation |
absolute dates | Isotopic Dating |
based on Parent/Daughter ratio when the decay is known | Isotopic Dating |
requires a closed system | Isotopic Dating |
no parent or daughter product can leave the system | closed system |
changes based on particle emissions/capture | Isotopic Dating |
parent nucleus loses an alpha particle | alpha particle emission (nucleus of helium atom) |
daughter atomic number is 2 lower | alpha particle emission (nucleus of helium atom) |
daughter atomic weight is 4 lower | alpha particle emission (nucleus of helium atom) |
parent nucleus loses a beta particle | beta particle emission (electron) |
neutron changes to a proton in the nucleus | beta particle emission (electron) |
daughter atomic number is 1 higher | beta particle emission (electron) |
daughter atomic weight is the same | beta particle emission (electron) |
parent nucleus gains a beta particle | electron capture |
proton changes to a neutron in the nucleus | electron capture |
daughter atomic number is 1 lower | electron capture |
daughter atomic weight is the same | electron capture |
14C dating - Carbon - Nitrogen - 1/2 life 5,730 years | Carbon dating |
in atmosphere 14N + e --> 14C + H | Carbon dating |
14C + O2 --> 14CO2 into plants and animals | Carbon dating |
dates 14C/12C after death | Carbon dating |
normal methods good to ~40,000 years | Carbon dating |
accelerator dates to ~100,000 years | Carbon dating |
tree rings used to calibrate dates | Carbon dating |
14C production assumed constant through time | Carbon dating |
14C disappears at the 1/2 life rate- 14 14 6 C --> 7 N - " decay | Carbon dating |
Earth age = 4.6 billion | Uranium-Lead dating |
1/2 life = 713 million to 4.5 billion years | Uranium-Lead dating |
dated oldest rocks on Earth | Uranium-Lead dating |
Zircon U/Pb age - 4.06 Ga | oldest rocks |
Northwest Territories of Canada | oldest rocks |
gneissic rock type (Acasta Gneiss) | oldest rocks |
1/2 life 48.8 b.y. | Rubidium-Strontium dating |
discovered 1948 | Potassium-Argon dating |
1/2 life = 1.3 b.y. | Potassium-Argon dating |
40Ar/39Ar method | Potassium-Argon dating |
argon loss at 50-200o C | Potassium-Argon dating |
metamorphism resets the atomic clock | Potassium-Argon dating |
usually igneous rocks dated- biotite, others | Potassium-Argon dating |
1/2 life 106 b.y. | Samarium-Neodymium dating |
1/2 life = 13.9 b.y. | Thorium-Lead dating |
global | MAGNITUDE |
Cenozoic; specific events in time | TIME |
CaCO3; water in ice cores; mineral specific | MINERALOGY |
ice volume and climate | CAUSE |
evaporation and precipitation fractionation | INTERPRETATION |
diagenetic problems; organism specific, | ANALYTICAL |
good | PRECISION |
cycles - Cenozoic; event specific | UTILITY |
measured using mass spectrometers | oxygen isotopes |
rare isotopes | 180 |
common isotope | 160 |
lighter 16O more readily | during evaporation |
heavier 18O is left behind and concentrated | during evaporation |
ice is light-isotope enriched | during glaciation |
oceans become heavier | during glaciation |
in general, marine organisms concentrate 18O | during glaciation |
some organisms fractionate isotopes | problems with fractionating |
salinity causes local isotope anomalies | problems with fractionating |
temperature decreases and organisms concentrate 18O | problems with fractionating |
first identified by Urey in 1947 | fractionation |
method established by Emiliani beginning in 1954 | fractionation |
(1967) estimated paleotemperatures | Shackleton |
(1973) established $18O to 120 Ka | Shackleton and Opdyke |
record pushed back beyond 2 Ma | Shackelton |
(1984) | Imbrie and others |
established a well dated $18O composite to 780 Ka | Imbrie and others |
back to 500 k still used today as established in 1984 | Imbrie and others |
based on 5 marine cores | Imbrie and others |
showed Milankovitch periods | Imbrie and others |
precession at ~20 kyr | orbital |
obliquity at ~40 kyr | orbital |
at ~100 kyr | eccentricity |
the state of the atmosphere at a place and time as regards heat, cloudiness, dryness, sunshine wind, rain, etc., | weather |
the weather conditions prevailing in an area in general over a long period - classically defined as 30 yrs | climate |
of/or relating to the entire Earth as a planet | global |
as used by geologists represents the temperature, rainfall and wind over thousands of years | Global Climate |