read pages 9-11, (skim the rest of CH. 1) recommended that you look over pages 370-371, 374-377

Earth is 4.6 billion year old. Evidence from radioactive decay: (unstable atoms lose or gain particles and form new element at a known rate).

Example of half lives

If your parents had $1000 when you were born and gave you half of their money every 5 years:

• After 5 years (1 half life) ---  parents: $500, you: $500
• After 10 years (2 half lives) ---parents: $250, you: $750
• After 15 years (3 half lives) ---parents: $125, you: $875

As rocks form, radioactive elements are trapped inside.
Parent elements decays to daughter elements.
By counting up the number of parent and daughter elements, the age of the rock can be determined.

Using radiometric dating, oldest Earth rock has been dated as 4.3 billion years old
But, meteorites have been founded that are 4.6 billion years old.
Can infer that Earth is 4.6 billion years old if meteorites were formed at same time as the Earth was formed.

Formation of the solar system 4.6 billion years ago:

•  rotating, cloud of gas
• gravity causes the cloud to condense,
• Sun formed at center.
• Other material condenses to form planetesimals, which grew into planets

Heating led to melting and differentiation (making layers)

• denser elements sunk
• less dense elements  rose
• gases escaped to form atmosphere

In the mantle, rock is weak, and heat moves by convection (warm rock rises and cold rock sinks).
In the lithosphere, the rock is too strong to flow, so it transmits heat by conduction (the heat moves upward, but the rock doesn’t)

Earth's layers ( review Figure 1.8 in your text)
Crust.Two types:
 oceanic -- 5 to 10 km, more dense
 continental: 20 to 90 km, less dense
Mantle: more dense than crust, less dense than core Within the mantle: the asthenosphere is a weak, partially melted layer.
Crust and uppermost mantle form the lithosphere, which is strong and brittle.
 

Core of  iron, nickel    inner core: solid    outer core: liquid

Note: It might be surprising to you that the inner core is solide while the outer core is liquid.  Because heat increases towards the center of the Earth, you might expect that the inner core would be melted. However, pressure increases towards the earth's center also (from the weight of the overlying material). That high pressure raises the melting point of the iron/nickel core and keeps the inner core from melting.

How do we know about Earth’s interior?
• can calculate density from gravity.
• meteorites
• earthquake waves--  move faster through denser material, also, some types can’t pass through liquids.

If you're interested in meteorites: http://www.meteorite.ch
If you're interested in a tour of the solar system: http://seds.lpl.arizona.edu/nineplanets/nineplanets/