EARTH

1. Internally, the Earth is DIFFERENTIATED, i.e. segregated into layers according to density

Internal Structure of the terrestrial planets compared
Seismology P-waves (Pressure waves), S waves (Shear or transverse waves)

Inner core: Solid Nicel-Iron
Outer core: Liquid nickel iron
Mantle: semisolid (plastic) rock
Crust: Granites, basalts. Under the ocean, the crust is made of dense basalt, and is about 7 km thick; under the continents, the crust is made of lower density granite and is up to 30 km thick.

The Earth is layered because it underwent differentiation when it was young and molton.

2. The Earth is geologically active.

Today, radioactive decay of heavy elements results in heat which keeps the inner Earth warm and the geology of the Earth active.
Radioactive decay of Potassium (K), Uranium (U) and Thorium (Th)

The molten layers are constantly bubbling (convection), and the crust or lithosphere is broken into tectonic plates.

Convection in mantle

Plate Tectonics: Lithosphere currently is 7 large pieces, or plates

3. The modern continents were once connected, but have "drifted".
Motion of the tectonic plates causes earthquakes, shapes mountain ranges, etc.

Contenental Drift Animation of last 750 million years

Formation of the Hawaiian Islands
East Africa Rift Valleys
Sinai Penninsula Rift

San Andreas Fault
1906 Earthquake

4. Components of Modern Day Earth:

Atmosphere
Hydrosphere (water cycles in oceans, atmosphere)
Biosphere (plants and animals)

The Atmosphere of the Earth

Current Day Composition: 78% N₂, 21% O₂, 1% Argon

Trace: CO₂   (Carbon Dioxide)
        H₂O (Water)
O₃     (ozone)

c.f. Venus and Mars: 95% CO₂

The composition of the current-day atmosphere is the result of the biosphere on Earth.

Originally, the atmosphere was almost entirely CO₂ and water vapor, no O₂.
The modern atmosphere developed when

1. Limestone formed in the Oceans, tying up CO₂

Early marine creatures had shells of calcium carbonate, when they died,
the shells fell to the bottom of the ocean and made limestone

2. Plants appeared and converted CO₂ --> O₂ through photosynthesis,
beginning about one billion years ago.

The Hydrosphere

Water covers 71% of the surface of Earth
98% of the water is in oceans
If the Earth was a smooth, perfect sphere, a global ocean would cover the Earth to a depth of 2.25 km.

The Biosphere: Plants, Animals, Bacteria, Viruses, etc.

There are about 1.5 million described species; an estimated 3 million species exist on Earth today, but have not yet been described
Only 4000 species are mammals, or 0.025% of all species.
From the fossil record, it is estimated that living species today represent less than 10% of the number of species that have ever existed.
Coal, oil and natural gas are formed by the biosphere.

Impact Craters on Earth

Craters are very quickly (in geological terms) eroded away by water and wind.
Mass extinctions evident in the fossil record were probably caused by large impacts of asteroids/meteors.

Cratering on Earth

Global Warming

We can measure the CO2 concentration in the atmosphere as a function of time, using bubbles trapped in ice layers in Antartica. (Last 50 years, direct measure).

An steady increase in CO2 began in the mid-1800's, the result of increased burning of fossil fuels, associated with the growth of industry and urban populations.

The increased CO2 causes an enhanced "greenhouse effect" and hence warming of the average temperature on Earth.

Greenhouse Effect; Global warming from increased "greenhouse gas" production, particularly in the U.S.
Greenhouse Gas: CO₂, methane (from burning of coal, natural gas, and oil; livestock); nitrous oxide; hydroflurocarbons.

EPA Website:
"Global mean surface temperatures have increased 0.5-1.0°F since the late 19th century. The 20th century's 10 warmest years all occurred in the last 15 years of the century. Of these, 1998 was the warmest year on record. The snow cover in the Northern Hemisphere and floating ice in the Arctic Ocean have decreased. Globally, sea level has risen 4-8 inches over the past century. Worldwide precipitation over land has increased by about one percent. The frequency of extreme rainfall events has increased throughout much of the United States."

Depletion of the Ozone Layer

CFC's (chloroflurohydrocarbons) destroy ozone, which absorbs UV radiation.

The total ozone in the Earth's atmosphere is declining.

The Ozone Layer (O3)

The Earth's Magnetosphere & aurorae

The Earth has a magnetic field, which makes a cavity called the magnetosphere,
protects us from the solar wind (fast moving stream of protons and electrons from Sun).

Aurorae occur when solar wind electrons spiral into the upper atmosphere along
magnetic field lines and crash into atmospheric molecules and atoms.

Geological Dating

Radioactive dating of rocks shows that the oldest rocks are about 4.5 billion years old.

Radioactive Dating:

Parent nucleus decays to a daughter nucleus + energy + electrons and/or other particles

The decay rate can be characterized by a half-life, the time it takes half of a sample to decay.

      So if the half-life of a decay process is 10 days, and you start with 100 atoms,
   after 10 days, 50 atoms have decayed, 50 remain undecayed
   after another 10 days, 25 more atoms have decayed, 25 remain undecayed
   after another 10 days, 12-13 more atoms have decayed, 13-12 parent atoms remain,
                   and so on...

Different radioactive elements have different half-lives.
      U238 -> Lead-206                    4.5 billion years
       Th 232 --> Lead 208                 14 billion years
      Potassium-40 --> Argon-40       1.25 billion years
       Carbon-14 --> Nitrogen 14       5730 years
(The number is the number of protons + neutrons in the nucleus)

Important Clock: Potassium-Argon   (K --> Ar)

     Argon is a nobel gas, and doesn't interact with other elements.

   K40 on Earth was produced in stars which blew up before the solar system formed and polluted the solar nebula.

     Magma (molten rock) crystalizes, and cools, and contains some number of K40 atoms.

    The K40 atoms then decay into Ar40, with half-life 1.25 billion years.

    The Ar gas formed gets trapped in the rock.

    Careful measurement of the number of K40 atoms and number of Ar40 atoms tells you the time since the magma cooled.

Important Clock: Carbon-14

C14 is produced in upper atmosphere when cosmic rays (energetic protons and electrons) collide with Nitrogen molecules.
Nitrogen-14 decays to Carbon-14.
Normal (non-radioactive) carbon is Carbon-12.

So in the atmosphere, there's a fairly constant ratio of 14CO2 to 12CO2

Plants absorb CO2
Animals eat plants

When plants and animals are alive they have a constant ratio of 14CO2/12CO2 in their bodies, equal to the atmospheric ratio.

When they die, no more 14CO2 is being absorbed, and the 14C decays.

By measuring 14C/12C, you can measure the time since death.

Measures time back to about 50,000 years ago.

OTHER CLOCKS

1. Tree Rings

See Tree Ring Lab, founded by A.E. Douglas at the University of Arizona.

2. Ice Layers

Drill cores in Greenland and Antartic ice sheets --> record of past 65,000 years
Seasonal snow melt --> layers
Layers contain volcanic ash, heavy elements associated with the industrial revolution, CO2 levels

Iceberg in Antartica:

3. Varves

Thin layers of clay accumulate in still waters of some glacial lakes.
Frozen layer allows sediment deposited by that year's meltwater to settle.
Each layer --> 1 year

See layers of Varves in sedimentary rocks -- e.g. Green River shale: