inferring: brain barrel & earth's interior

without x-ray vision it is impossible to KNOW what is inside the brain barrel. However, by making observations ( including "ear witness evidence," ) taking measurements, gathering data the investigator can make a strong inference about its contents and workings.

many of the great "facts" of science are inferences. Let's examine one such piece of accepted knowledge: the composition and dimensions of earth's interior.

earth is 8,000 miles thick ( 12,880 km ), but the deepest sample of rock has been cored from only about 6 mi ( 10 km ). What is the composition of the remaining 4,994 miles "stuff" -- and how can they infer that ?

quaking earth and mind to a geologist collecting data for her dissertation in seismology ( size- mology ) an earthquake is a constructive force not a destructive one. When rock layers break and the planet quakes, many types of vibrations ( waves ) are emitted. By analyzing the speed and direction in which they travel ( and the directions they do not travel ) much can be inferred earth's innards.
First - let's examine features of sound waves and light waves & transfer this information to EQ waves.

analogy: compare sound waves to EQ waves

Kids can't experience EQ waves, but they can hear the sound of a . . .

tuning fork
clothes hanger

to compare sound waves when they travel thru -

air
body tissue
bone

and infer that the difference in the intensity is due to the material ( conductor ) thru which it traveled.

some EQ waves are like sound waves { Primary ( P ) Waves }.

Students assume that P-waves intensity is also influenced by its conductors.

analogy: compare light waves to EQ waves

Kids can't experience EQ waves, but they can see light passing thru . . .

air
water
cooking oil

and infer that the differences seen in the direction is due to the material thru which it traveled.

some EQ waves are like light waves { Secondary ( S ) Waves }

Students assume that an S-wave direction is also influenced by its conductors.

in a nutshell: to make a long, long story "fit on two pages"

By studying sound and light waves, scientists transfer their findings to interpret the behavior of EQ waves and construct a "map" of the probable structure of earth's interior.

observe: lab tests: EQ waves speed varies with the rock type
wave theory: a change in speed causes bending ( refraction )
infer: since speed / direction of EQ waves varies - earth's composition varies
observe: some areas on earth surface do not receive any EQ waves
infer: at great depth the rock ( "liquid" ) absorbs EQ waves

all of this data is interpreted to mean that earth has these zones:
- inner core: 3100 to 4000 mi --- 5000-12,880 km

Note: EQ damage is done by Longitudinal ( L ) Waves moving along the earth's surface. They are not use in determining earth's deep [ interior composition. ]

4 / 5w / 94
11 / 27m / 95