How old is it

1
How old is it?
2
Working out dates

• Dendrochronology
• Magnetic Dating
• Carbon 14
• Thermoluminescence
• Fission Track Dating
• Potassium / Argon Dating

3
Dendrochronology

• Tree Ring Dating

4

• Trees show annual growth rings that can be easily
  counted.
• This technique can give dates to around 10,000
  years ago.

5
Bristle Cone Pines

• The oldest Bristle Cone discovered so far was
  4,900 years old
• Many are 4,000 years old.
• These trees were already 2000 years old during
  the time of the Cesars.

6
Magnetic Dating

• The direction and strength of the Earths
  magnetic field is constantly changing.
• Field fixed in molten stone or fired clay.

7
Paleomagnetism

• Correspondence between the locked magnetic
  polarities of different layers of lava flows and
  the magnetic-reveral time scale

8
Radioactivity
9
The structure of an Atom

• All atoms are built from the same basic
  components.
• Protons and neutrons are found in the nucleus.
• Electrons are found in orbits around the nucleus.

10
Carbon 14 in the Atmosphere

• Carbon 14 undergoes constant decay.
• C14 ratios remain relatively stable in the
  atmosphere.
• C14 is constantly formed in the upper atmosphere.

11
Carbon 14 Decay to Nitrogen 14

• Carbon 14, and unstable isotope of Carbon, loses
  an electron and decays into Nitrogen.

12
Carbon 14 and Living Things

• Organisms are constantly replenishing their
  carbon and so while living maintain the same C14
  ratios as found in the atmosphere.

13
Exponential Decay of Carbon 14

• ½ of the Carbon 14 decays every 5730 years

14
Practical use of Carbon 14

• Bison from Ornee Caves in Niaux, France
• Dated by Carbon 14 technique to be 13,000 years
  old
• Objects can be dated as old as 70,000 years old

15
Thermoluminescence

• Materials are exposed to a constant flux of
  ionising radiation.
• When crystalline materials are exposed to
  ionising radiation, a redistribution of
  electrical charge takes place within the crystal.
  
• A small fraction of it can become trapped for
  long periods in higher energy states.
• The extra energy that the crystal contains as a
  result of the radiation exposure can be released
  by heating the material.
• If the crystal is then cooled and re-heated it
  does not re-emit light, because the energy excess
  which produced the first emission has now been
  released from the crystal.

16
Thermoluminescence

• Natural materials which may be dated by TL are
  flint (or stone), stalagmitic calcite, and
  sediments.
• Ceramics are also datable by TL.
• Objects can be dated up to around 70,000 years
  old.

17
Thermoluminescence test

• A pair of early Tang small seated pottery
  musicians.Tang dynasty (AD 618-906)

18
Fission Track Dating
19
Fission Track Dating

• fission track analysis is widely used as a means
  of dating minerals
• Observing the tracks made in objects by the
  fission fragments of the uranium nuclei that they
  contain.
• Objects are irradiated with neutrons to induce
  fission then the density and number of the tracks
  before and after irradiation is noted to estimate
  the time that has elapsed since the object
  solidified.
• Objects can be dated to 10,000,000 years old

20
Potassium-Argon Dating

• Potassium-Argon dating is the only viable
  technique for dating very old archaeological
  materials. Geologists have used this method to
  date rocks as much as 4 billion years old.

21
Potassium-Argon Dating

• One out of every 100 Potassium atoms is
  radioactive Potassium-40 (K-40). For every 100
  K-40 atoms that decay, 11 become gaseous Ar-40.
• When rocks are heated to the melting point, any
  Ar-40 contained in them is released into the
  atmosphere. When the rock recrystallizes it
  becomes impermeable to gasses again. As the K-40
  in the rock decays into Ar-40, the gas is trapped
  in the rock.

22
Potassium-Argon Dating

• Dating is indirect and based on finding
  non-volcanic material between igneous strata

23
Radioactive Decay

• A powerful tool to discern age of certain
  objects.
• The usefulness of any given isotope depends on
  its half-life.

24
Cited Figures

• Magnetic dating and spreading plates
  http//www.kie.berkeley.edu/ned/data/E01-971212-00
  8/E01-971212-008.html
• Bristle Cone Pine http//web.utk.edu/grissino/i
  mages/bcp.jpg
• Growth Rings http//emuseum.mnsu.edu/archaeology/
  dating/images/tree_ring.gif
• Magnetic dating by period http//geomag.gly.fsu.e
  du/parker/1000/seis/1000seis.htm
• Exponential Decay of C14 http//carbon14.univ-lyo
  n1.fr/courb2.gif
• C14 in the atmosphere http//www.cnde.iastate.edu
  /ncce/RT_CC/Sec.2.4/c-14b.gif
• Carbon 14 Decay to Nitrogen 14
  http//sol.sci.uop.edu/jfalward/nuclearphysics/ca
  rbon14decay.JPG
• Bison from Ornee Caves in Niaux, France
  http//www.laradioactivite.com/pages/05_laboratoir
  e/01_methodes_d.htm
• Thermoluminescence test http//www.yang-guifei.co
  m/Welcome.html
• Fission Track Dating http//bullard.esc.cam.ac.uk
  /hobro/fission_image_hires.gif
• Potassium-Argon Dating http//anthro.palomar.edu/
  time/images/potassium_argon_dating.gif
• Radioactivity http//www.wps.com/archives/FilmStr
  ips/Effects-of-Fallout/atoms-are-unstable.GIF
• The structure of an Atom http//info.fuw.edu.pl/f
  estiwal/2001/struny/czastki/atom.gif
• Radioactive decay http//earth.leeds.ac.uk/dynami
  cearth/dating/decay.gif
• Carbon 14 and Living Things http//jan.ucc.nau.ed
  u/wittke/GLG100/Carbon14.jpg