1. These power point presentations accompany the readings in the text
These power point presentations accompany the readings in the text. In some cases additional material will expand on the text. In other cases, the power points will emphasize what is most important in the text.

2. Comments on “The Earth as a Habitable Planet” p. 2-3 in text
Comments on “The Earth as a Habitable Planet” p. 2-3 in text. Be familiar with the terms in bold lettering. Also remember this number: 71% of the Earth’s surface is covered by oceans.

3. A few comments on Fig. 1.1 in the text:
Countless geological, physical, chemical, biological, and atmospheric interactions are taking place on and within the Earth.
The following figure divides the Earth into five systems or spheres. The arrows represent the interactions among the spheres.

4. p. 3

5. The interactions can be illustrated with a few examples.
In the geosphere, the Earth’s internal heat causes volcanoes and hydrothermal vents which release lava, steam, and carbon dioxide.
The steam adds water to the ocean and atmosphere.
The carbon dioxide dissolves into the ocean or enters the atmosphere.
The internal heat causes the mantle to convect thereby producing seafloor spreading and continental drift.

6. Chemical interactions between the lava and seawater change the chemistry of both the lava and seawater.
Through photosynthesis, plants use the energy of sunlight to extract carbon from carbon dioxide and incorporate it into the biosphere.
Through respiration and bacterial decay of dead plants and animals, the carbon dioxide and water are cycled back into the oceans and atmosphere.
The energy of sunlight evaporates water and adds water vapor to the atmosphere.

7. Water vapor condenses into rain and snow which fall on the land to chemically weather the soil and rocks, physically erode the land, and take the dissolved chemicals and sediment to the ocean via rivers.
Chemical and detrital sediments deposited on the ocean floor and the water soaking the sediments are carried down subduction zones to be incorporated into the interior of the Earth, heated by the Earth’s internal heat, and released back into the hydrosphere and atmosphere via volcanic and hydrothermal activity.

8. Growing glaciers extract water from the atmosphere and hydrosphere and add mass to the crust causing it to subside.
Melting glaciers add water to the atmosphere, hydrosphere and biosphere, and their disappearance unloads the crust and causes it to isostatically rebound.

9. Here are two examples of heat engines
Here are two examples of heat engines. Heat energy is being converted into mechanical energy.

10. The interactions among the spheres are being driven by two heat engines.
One heat engine is driven by the Earth’s internal heat that has been produced by the radioactive decay of isotopes and by the original accretion and density stratification of the Earth.
The heat is exiting the interior by conduction (the transfer of heat from atom to atom) and convection (the mass currents in the mantle and core).
The external heat engine is driven by the radiation from the sun.

11. Comments on “History of the Earth” p42-43
Comments on “History of the Earth” p These are some of the basic things about the early history of the Earth, I want you to know: *The Sun, Earth and other planets of the solar system formed as the gases, dust, ice and rocky material in space accumulated because of the force of gravity. This is called accretion. *This happened about 4.56 billion years ago (a good number to know).

12. *The Earth heated up because the accretion of material under gravity produces heat and because of the heat of naturally radioactive isotopes that was included in all that accreted material. *The Earth became molten and density stratified. That’s a fancy term meaning the heaviest materials sank to the center of the Earth and the lightest, like the steam and gases erupted from many volcanoes, formed the early atmosphere. *The early atmosphere was mostly N2, H2O, CO2, and HCl – the common volcanic gases.

13. *The oceans formed when the Earth cooled enough that steam could condense into water. *The water was acidic because of the CO2 and HCl dissolved in it. *This caused chemical weathering of crustal rocks which released many ions into seawater. *In addition the volcanoes released excess volatiles into seawater. *Ions from chemical weathering and volcanic eruptions dissolved in seawater made it salty.

14. Some comments on Fig This is a complicated diagram, but these are the things I want you to know (see next page).

15. The Earth formed about 4. 6 million years ago
*The Earth formed about 4.6 million years ago. *The early environment was oxygen-free (called anoxic). *The first life, anaerobic bacteria, evolved before 3.5 billion years ago. *The roughly 3.5 billion years the first photosynthetic bacteria (cyanobacteria) evolved. They were the first to produce free oxygen. *These first organisms were marine, not terrestrial.

16. Over time the free oxygen increased in the ocean and atmosphere
*Over time the free oxygen increased in the ocean and atmosphere. *The first multicellular organisms evolved. *The “Cambrian explosion” occurred around 543 million years ago. This was a rapid, significant increase in the number of organisms with shells, possibly related to the increase of oxygen in the environment. *Based on the fossil record, the first land organisms appeared shortly after this. *Life didn’t always keep advancing steadily. At times there were mass extinction events.

17. *We will be covering ocean biology later in the session, at which time we will cover the other biological terms mentioned in this section

18. Now to discuss Fig. 2. 10 in your text
Now to discuss Fig in your text. The following slides describe what I would like you to take away from this figure. The underlined terms are important to remember.

19. The Earth is internally layered and density stratified.
*Density stratified means that the layers (strata is the Latin term for layer) are arranged according to density with the lightest material on top and the heaviest material at the center of the Earth.
*The atmosphere is the lightest and is above everything else. The oceans which are the next lightest, form an incomplete layer below the atmosphere.

20. The lithosphere is the rigid shell of the Earth
*The lithosphere is the rigid shell of the Earth. The upper part of the lithosphere, the part we walk on, is called the crust. The boundary between the crust and the rest of the mantle is called the Moho.

21. *The lithosphere is not one piece, but it is broken into plates that move relative to each other. The continents are parts of these plates and so they move around also; this is called continental drift.

22. * These plates are moved, to a first approximation, by convection currents in the mantle.

23. *The mantle is immediately
below the lithosphere and
is not completely rigid, but
over geologic time can flow
slowly in giant convection
currents somewhat like the
convection currents in this beaker of molten wax.
The mantle is heated on the bottom by the very hot core. The temperature difference between the hot bottom of the mantle and the cooler top of the mantle drives the convection.

24. *The core is at the Earth’s center; it is the densest and hottest part of the Earth. It is divided into a liquid outer core and a solid inner core.
*In general temperature, density and pressure increase from the Earth’s surface to its center.

25. Now to say a little about the chemistry of these layers:
*The crust consists of the continents and ocean basins. While we can see many kinds of rocks on the continents, the average composition of the continents is granitic. Granite is a silicate igneous rock comparatively rich in the elements aluminum, potassium and sodium. Under the sediments the ocean basins are mostly made of the silicate volcanic rock called basalt. Basalt is comparatively rich in iron, magnesium, and calcium. Basalt is darker and denser than granite.
*The mantle is consists of other types of silicate materials, not granite or basalt.
*The core is much different. It is mostly iron with essentially no oxygen or silicon. It is the densest part of the Earth.

26. Now to say a little about the chemistry of these layers:
*The lithosphere with its crust, and the mantle are made of silicate materials for the most part. Most (but not all) of the rocks you see walking around on the Earth’s surface are silicate materials.
*Silicate materials are made up mostly of two elements: oxygen (O) and silicon (Si). All the other elements make up smaller proportions of natural silicate materials. Since most of the rocks you see are silicates, the adjective “rocky” roughly means silicate for us.

27. *The crust consists of the
continents and ocean basins.
While we can see many kinds
of rocks on the continents,
the average composition of
the continents is granitic.
Granite is a silicate igneous
rock comparatively rich in
the elements aluminum,
potassium and sodium. Under the sediments the ocean basins are mostly made of the silicate volcanic rock called basalt. Basalt is comparatively rich in iron, magnesium, and calcium. Basalt is darker and denser than granite.

28. Here are some pictures of granite: and basalt:

29. Now don’t get overwhelmed by all the density and depth numbers mentioned in Fig. 2.10, you don’t have to learn them.
One thing to note is that below the crust the rest of the lithosphere has a chemical composition more like the mantle, so that in chemical terms the lower lithosphere is lumped in with the mantle. Whereas when considering physical properties, such as rigid vs. soft and flowing, the lithosphere is separated from the mantle. A little confusing, but the following two figures in color better illustrate this than the gray-shaded Fig
Please note that the lower mantle (mesosphere) is labeled rigid. That is not really true, it can still flow though not as quickly as the upper mantle (asthenosphere).

30. Layering of the Earth

31. Upper Layers of the Earth (note that the flowing ashenosphere is just below the lithosphere).