Heat Sources for Melting of Primitive Earth

1
Heat Sources for Melting of Primitive Earth

• Unstable Nuclides and Gravitational Compression

2
Belt of Stability
Stable nuclides have N/Z ratios from 1 to 1.52.
All nuclides that lie outside this belt are
unstable and undergo nuclear reactions until they
become a stable nuclide.
3
Radioactivity

• Process in which an unstable nucleus is
  ultimately converted to a stable nucleus by means
  of nuclear reactions
• All nuclei having Z gt 83 and a few having Z lt 83
  are unstable
• The emission of energetic particles during a
  nuclear change is called radiation

4
Types of Radiation
Buell/Girard, "Chemistry", Prentice Hall,
NJ,1994, 152
5
Natural Radiation
Tro, 185
6
Penetrating Power
http//www.princeton.edu/ehs/radtrain/Modules/bas
ics.html
7
Equations for Natural Radioactivity
Alpha Radiation
Beta Radiation
Gamma Radiation
8
Half-Life

• Half-life is the time required for half of the
  radioactive nuclei in a sample to decay
• After n-half-lives, the fraction of the original
  radioactive nuclei still remaining is 1/2n

9
Half-life
Joesten et al, Chemistry Impact on Society,
Saunders, NY, 1988, 68.
10
Joesten/Wood, "World of Chemistry,2nd,
Saunders,PA, 1996,122
11
Estimating the Age of Rocks Based on U to Pb Decay
Oldest rocks found on surface of Earth contain
50U and 50 Pb. Estimate the age of planet Earth
Tro, 202
12
Estimating Ages of Materials that Contain Carbon
Half-life 5730 yr
13
Carbon Dating
Object
Tro, 200
14
Radioactive Decay and Heating of Primitive Earth

• The shorter the half-life, the faster a nuclide
  decays
• Radiation is accompanied by a release of heat
  energy
• Unstable nuclides formed during a supernova
  decayed at a rapid rate, released much heat which
  contributed to the melting of planet earth

15
Heating of Earth Due to Gravitational Compression
Miller, F.M., Chemistry, Structure and Dynamics,
McGraw-Hill, NY, 1984, 715