10.1 Earth and Space

Mr. H

Principle of uniformitarianism

The idea that the same natural process we see today have always happened

Law of Superposition

In rock layers, the oldest rocks are at the bottom, and the youngest are at the top

Law of cross- cutting relationships

If a rock or fault cuts through another, it is younger than the rock it cuts

Relative age

The age of something compared to other things (not the exact number of years)

Absolute age

The exact age of a rock or fossil in years

Index fossil

Fossils of organisms that lived during a short, specific time and are found widely; used to date rocks

Trace fossil

Evidence of an organism’s activity (like footprints or burrows), not the organism itself

Imprint fossil

Fossils that form from an organism leaving a mark or impression in rock

Unconformity

A gap in the Rock record caused by erosion or lack of deposition

Half- life

Time it takes for half of a radioactive substance to decay

Angular conformity

Rock layers are tilted and then eroded before more layers are added on top

Nonconformity

When sedimentary rocks lie on top of older eroded igneous or metamorphic rocks

Disconformity

A gap in time between two sedimentary Rock layers

Principal of faunal succession

Fossil organisms follow one another in a predictable order through rock layers

Petrification

The process of turning organic material into stone by mineral replacement

Nitrogen- 14

What does carbon - 14 decay into

sedimentary rock

What type of Rock are fossils primarily found in

a. lived for a short time

b. found in many places

c. easily recognizable

d. abundant (found in large numbers)

e. only found in specific Rock layers

What is the criteria to be considered an index fossil

helps determine the absolute age of rocks and fossils

Why is radioactive decay so useful

lead- 206

What does uranium- 238 decay into

a. by measuring the ration of parent to daughter isotopes and knowing the half- life.

How is radiometric dating used to find the age of rock layers

comparing fossils in rock layers to index fossils of known ages

how are fossils used to find the age of rock layers

how does a mold fossil form

when an organism’s body leaves an impression in the sediment, which hardens into rock

two half- lives have passed (25% left means 2 half- lives), so it is 20 years old

You found a sample that is 25% uranium (parent) and 75% lead (daughter). How old is the sample? half- life = 100 years

If a sample were to go through 6 half-lives, what percentage of the parent would be left?

a. Isotopes have different numbers of neutrons but the same number of protons

b. Ions have different numbers of electrons, which gives them a charge

What is the difference between isotopes and ions