Integrating Chemistry into SCI 210 The Dynamic Earth

Andrea Koziol, Dept. of Geology

Chemistry in Earth science

• Chemical concepts actually quite pervasive

• Touched on in lecture in a number of instances

Emphasized in these areas

• Minerals• Energy and mineral resources• Greenhouse effect (action of CO2

molecule)• Chemical weathering• H2O changes of state, latent heat (clouds

and weather)• Ozone in the stratosphere• Numerical dating with radioactive isotopes

Crystalline nature

• Orderly internal arrangement of atoms in a lattice

• A specific pattern that repeats at regular intervals

minerals

Oil and gas

• Oil and gas are hydrocarbons: chains or rings of C and H

• React with O2 to form gas and heat energy

• For example:

• 2 C8H18 + 25 O2 = 16 CO2 + 18 H2O + heat energy

Natural resources

This is the Greenhouse Effect

• Water and CO2

molecules absorb this heat energy

• The atmosphere is heated from the ground up

• This heat stays in the atmosphere

Infrared

H2O CO2

Greenhouse effect I

Chemical Weathering

• Chemical weathering: destruction or altering of minerals when rock comes in contact with water solutions or air.

• Examples:

• Dissolution by water or carbonic acid, oxidation, reaction to new minerals

weathering

Chemical weathering examples

• Dissolution by carbonic acid: CO2 dissolves in H2O (rain) to form weak carbonic acid (H2CO3) which attacks limestone, marble

weathering

Moisture and Clouds

• It’s about H2O and changes in state:

• Ice --- liquid --- water vapor

Atmosphere II

Latent heat (hidden heat)

• Latent heat: heat added that is not associated with temperature changes. It is energy absorbed or released during a change in state.

• Storing this latent heat, moving it around, is important!

Atmosphere II

Global: CO2, Greenhouse Effect, Global Warming

• Today: CO2 concentration in our atmosphere is >0.036 % or 360 PPM

• If less CO2: cooler temperatures and cooler climate

• If more CO2: warmer temperatures and warmer climate

Global climate change

Most up-to-date infoGlobal climate change

What is ozone?

• Oxygen molecule: O2

• Ozone molecule: O3

• Very little ozone in troposphere

– What is there is a pollutant

• 90% of ozone is in the stratosphere

Ozone

How this works, cont’d.

• O3 + UV light energy = O2 + O (UV light totally absorbed)

• O2 + O recombine rather

quickly

• Reaction repeats

• UV light from Sun almost totally absorbed

Ozone

Parents and daughters

• Starting radioactive isotope: parent

• After decay, it’s different: daughter

• The number of protons, neutrons have changed by radioactive decay

• Example: carbon-14 (6 protons, 8 neutrons) decays to nitrogen-14 (7 protons, 7 neutrons)

Numerical dating

Rate of decay• How a parent atom decays, and rate of

decay is fixed.• Rate of decay doesn’t vary, no matter

what physical or chemical conditions the isotope is in.

• Every parent atom produces one kind of daughter

• So: look at amount of parent left, amount of daughter present.

Numerical dating

Now: radioactivity

• Radioactive decay is not linear.

• It is exponential. (see fig.10.14, decrease in # of parent isotopes as time passes)

Numerical dating

Radioactive decay example• Start with 160 parent atoms in our sample. How

much time has passed?• T = 0 half-l. 160 parents 0 dau.• T = 1 half-l.80 parents 80 dau.• T = 2 half-l. 40 parents 120 dau.• T = 3 half-l. 20 parents 140 dau.

• Look at ratio of parents to daughters to tell time.

Numerical dating