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all about geology
The first thing you should know about rocks is that the people who study them are known as geologists. Geologists don't study just rocks, they study the Earth—our home. And, just like doctors, geologists have specialties…
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time codes
  1. Physical Geology 1:02:39
    1. Dating 1:03:29
      1. Relative dating 1:03:45
      2. Absolute dating 1:04:10
    2. Time 1:04:15
      1. Eons, eras, periods, epochs 1:04:50
      2. Pre-Archean Eon, Archean Eon, Proterozoic Eon 1:05:36
  2. Fundamental Principles of Geology 1:05:36
    1. Geologic Record 1:06:12
      1. Sedimentary rocks 1:07:01
      1. Lithification 1:07:04
    2. Principle of Original Horizontality 1:09:19
    3. Principle of Superposition 1:10:53
    4. Principle of Lateral Continuity 1:11:22
    5. Law of Cross-Cutting Relationships 1:11:47
    6. Fossil Succession 1:12:42
    7. Principle of Uniformitarianism 1:13:54
  3. What Are Rocks Made of? 1:14:51
    1. Minerals 1:14:51
    2. Physical Properties 1:15:05
    1. Hardness 1:15:10
      1. Mohs hardness scale 1:15:17
    2. Cleavage 1:15:54
    3. Fracture 1:16:10
    4. Luster 1:16:53
    1. Metallic 1:17:05
    2. Nonmetallic 1:17:16
  4. Magma and Lava 1:18:14
    1. Igneous Rocks 1:18:42
      1. Extrusive 1:18:54
      2. Intrusive 1:19:21
    2. Lava Flow 1:19:53
      1. Pahoehoe flow 1:20:09
      2. Aa flow 1:20:35
    3. Pyroclastic materials 1:20:58
      1. Ash 1:21:07
      2. Pumic 1:21:25
      3. Tuff 1:21:42
    4. Volcanic Edifices 1:22:17
      1. Shield Volcanoes 1:22:31
      2. Composite Volcanoes 1:22:31
      3. Cinder Cones 1:22:47
      4. Fissure Eruptions 1:23:11
        1. Basalt plateaus 1:23:11
        2. Nuèe ardente 1:23:27
1. What stereotypes do you think people have about geologists? Even if geology isn't your favorite subject, what aspects of geology do you think attracts people to the field?

2. How is a volcano eruption similar to a snowfall? How is it different?

3. Which other field of discipline do you think geology has most in common with? Biology? Chemistry? Ecology? Or something else entirely?

4. What's the difference between magma and lava?

5. Scientists can predict fairly accurately how often a section of a country will flood over a 10-year period. If scientists knew that there is a 90% that an area would have a major flood every ten years, do you think people should be allowed to live there? Why or why not? Also, do you think home insurance companies should be required to insure homes in that area?

So You Want To Be a Rock Star

Have you ever wanted to make "rock" music? Here's your chance.

You can make several types of musical instruments with rocks you might find in a park or gravel path. After you make these instruments (and any others that you can think of) grab a few friends and start jamming.

1. Pebble Maraca
Gather a few handfuls of pebbles and drop them inside an empty coffee can or small milk container. Then put on the lid and start shaking! Try hitting different parts of the container to get more sounds. Also, you can fill the container with a little water to get a softer sound.

2. Drums
Find a medium rock and one large rock. Use the two rocks on a hard surface to make a beat. (Note: Make sure you own the surface you are hitting the rocks on. The rocks might bang it up a bit).

3. The "Bouip" Machine
Find a handful of palm-sized rocks. Then get three to four long, plastic cups and fill them with different amounts of water. Drop the rocks in different glasses. See how they sound? You can make different "bouip" sounds by playing with the amount of water, the size of the rocks, and how high you drop them.

4. The Clapper
Find two rocks that are very close together in size. Hold one in each hand and lightly tap them together. Not only will you avoid breaking the rocks by tapping them instead of hitting them, but the sound will be more pleasant to the ears.

Music Hints

• Start off with just one instrument, and play it for 30-45 seconds. Then slowly introduce the other instruments, one by one. This will help the dramatic tension in your music build. The drum is a good instrument to start off with because you can establish a steady rhythm with it and base the rest of the music off the beat.

• Rocks tend to make sounds that are harsh to the ear. Try playing your instruments gently to make then sound better.

• Midway through your song, when three or more instruments are playing at the same time, stop playing all of the instruments except one. Then slowly introduce the other instruments back in.

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coming soon!

Scientists believe Earth was formed 4,600 million years ago. That's a big number — not quite as big as the number of burgers sold by some burger chains, but still pretty big.
aa — A type of lava flow characterized by its lumpiness and viscosity. When it cools, the rock it forms may be sharp.

absolute dating — A technique that geologists use to assign specific dates to rock formations and geologic events.

ash — A substance that shoots out of a volcano that's two millimeters or smaller in diameter.

cleavage — The way crystalline minerals split or break along an even plane (planar surfaces).

cross cutting relationships — A fundamental principle of geology, which states that rocks that cut through other rocks are younger than the rocks being cut.

faunal & floral
— A fundamental principle of geology, which states that unless disturbed, the oldest fossils in a rock bed should be at the bottom.

fracture — In rocks, a break along an uneven (non-planar) surface.

geologists — Cool guys and gals who study rocks and the Earth.

hardness — A rock or mineral's ability to resist abrasion.

igneous rock — A rock that forms when molten rock cools down and crystallizes.

lateral continuity — A fundamental principle of geology, which states that sediments are deposited initially in a layer that extends horizontally in all directions.

lava — Hot, melted rocks that reach the Earth's surface.

lithification — The process that turns sediment into sedimentary rock.

luster — The way that minerals reflect light. There are two types of luster: metallic and nonmetallic.

magma — Hot, melted rock that's below the Earth's surface.

Mohs hardness scale — A scale that measures and compares the hardness of minerals.

original horizontality — A fundamental principle of geology, which states that sediments settle and accumulate horizontally on the sea floor.

pahoehoe — Congealed surface lava is dragged along over hot-moving lava. The congealed part rolls over the hot part, forming folds that look like ropes.

pumice — A form of volcanic glass that's filled with holes. These holes form when gases escape from lava.

relative dating — A technique geologists use to assign a sequential order to the age of rocks and geologic events. The oldest comes first, and subsequent events follow on a relative dating line.

— Rocks formed from things like little pieces of gravel, sand, silt, and clay, as well as the remains of animals and plants.

A fundamental principle of geology, which states that if a rock bed hasn't been disturbed since it was formed, it is younger than the layer of rock below it.

tuff — A type of igneous rock formed by the consolidation of ash.

— A fundamental principle of geology, which states that we can understand geologic events of the past by looking at geologic events of the present. According to uniformitarianism, a volcano eruption that happens today is pretty much like a volcano eruption that happened million years ago.

Check out this cool resource from the U.S. Geological Survey!

Like volcanoes? You'll love this site—Volcano World!

How about earthquakes? Learn all about them here!

Don't forget about us minerals!

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