• human history time scale

• earth history time scale
• example: earth's first atmosphere

A.   Human Records

1. meteorological records: NCDC and NASA
   • thermometer history?
   • only extreme events recorded?
   • How long? How many thermometers?
2. plant/agricultural records
   • crop yields
   • harvest dates; blossoming date
3. human histories
   • journals, gov records
   • paired photographs (before/after)
     • USGS "Repeat Photography Project"
   • sea ice or canal/river dates of freezing / thawing
     • Thames "Frost Fairs": 1683-84; 1814
     • Venice, Italy - 1709
4. archaeological evidence

1. tree rings / taking a core sample
2. Bristlecone Pines ... reconstructing a climate record / example of results
3. tree rings: problems

1. surface layers / drill bit / ice cores / another core / ice core layers
2. data from ice core
3. contamination? 1 , 2 , 3 , 4 , 5 (note the surgical mask), 6 (microbiological sample!)

E.   Pollen (palynology) and Pack Rat Middens

1. pollen studies: assumptions in interpretation
   • type(s) of vegetation present originally?
   • natural interference? wildfire? windy storms?
   • succession in progress?
2. radiocarbon dating used (see below)
3. middens found up to 40,000 years old
   • crystallized urine (slows decay of material)
   • arid climate = desiccates material
   • middens in caves = protect from weathering

1. what is a model?
2. global circulation models (GCMs)
   • predictions
   • mapped

II.   MECHANISMS, PROCESSES, THEORIES

A.   Dating Methods

1. carbon dating
   • atoms: protons & neutrons surrounded by electrons
     • atomic weight = protrons + neutrons
   • carbon = 6+6 = ¹²C
     • ¹²C ≈ 99% of all carbon on Earth (¹³C ≈ 1% of all carbon)
   • the value of a proton: 6 protons = carbon; 7 protons = nitrogen
   • ¹²C vs. ¹⁴C vs. ¹⁴N
   • ¹⁴N = 7 protons, 7 neutrons
     • electron collision (via solar radiation) can change proton to neutron
     • = 6 protons, 8 neutrons = ¹⁴C
   • method only works on biological material
     • once dead, ¹⁴C will lose neutron = ¹⁴N
     • half-life: ¹⁴C = 5700 years
     • video explanation ... or this video
   • assumptions:
     • solar radiant energy constant
     • decay rate constant
     • amount of C and N constant (since time of death)
     • calibration using tree ring data
       • i.e. carbon dating did not match tree rings
         • tree rings = 4K yrs vs. ¹⁴C = 600-700 years off
       • assumption: tree rings more accurate than ¹⁴C
       • assumption: that tree rings = one per year
     • etc.
     • Purdue-Stanford Research finding: half-life NOT constant
   • accuracy? error margin... 50,000 year limit
     • glacier = 25K yrs vs. peat under glacier = 11,400 yrs
     • burning of fossil fuels? = increases ¹²C = ¹⁴C ratio diluted
     • nuclear tests and explosions? = ¹⁴C increased
2. potassium/argon dating
   • no Ar in new minerals (lava/magma); ⁴⁰K decays to ⁴⁰Ar
     • i.e. fresh lava / magma should = 0 Ar
   • assumptions:
     • proportions of K-Ar same as today
     • no Ar to begin with in sample
     • *problem: some lava today shows presence of Ar
3. rubidium-strontium dating and other methods