1.5 Building Blocks and Dating

Question 1

what materials are present in interstellar clouds shortly after supernovas

Answer 1

products of nucleosynthesis, silicate minerals, organic molecules

Question 2

what is a mineral

Answer 2

molecules (two or more atoms held together by a chemical bond) that follows this definition

• a naturally occurring, inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form and physical properties

Question 3

is halite (rock salt) a mineral

Answer 3

yes, it is naturally inorganic (forms via evaporation of sea water)
yes, it has an orderly internal structure (repeating pattern of atoms)
yes, it has a characteristic chemical composition (NaCl)
yes, it has a characteristic crystal form (forms cubic crystals)
yes it has physical properties (hardness and density)

Question 4

what are the most common minerals

Answer 4

silicate minerals

Question 5

what are silicate minerals

Answer 5

atom of silica, four oxygen surrounding (overall charge -4)

Question 6

what is the most common mineral in the crust

Answer 6

feldspar

Question 7

what is the most common mineral on earths surface

Answer 7

quartz

Question 8

what are some non silicate minerals

Answer 8

calcite, halite, pyrite and hematite

Question 9

what are some metals that are non silicate minerals

Answer 9

gold silver and copper

Question 10

how do minerals form

Answer 10

1) random atoms
2) initial nucleation (combination of atoms)
3) additional molecules add in regular order

Question 11

how do minerals form

Answer 11

1) molten rock (minerals form from cooling magma)

2) precipitation from aqueous solution

3) metamorphism

4) weathering

5) biological precipitation

Question 12

how does speed of magma cooling effect size

Answer 12

rapid - small
slow - large

Question 13

what is metamorphism

Answer 13

rock and minerals changing under increasing temperature and pressure, new minerals can form from elements within existing minerals

Question 14

example of biological precipitation

Answer 14

shells, bones, teeth

Question 15

what are rocks

Answer 15

aggregates of minerals

Question 16

explain rock cycle

Question 17

how do we date rocks

Answer 17

radioactive decay

Question 18

isotopes vs atomic mass

Answer 18

same atomic number (Z) , different neutrons

Question 19

what is alpha decay

Answer 19

ejects two protons and 2 neutrons (atomic mass decreased by 4, atomic number decreased by 2)

changes element

Question 20

what is beta decay

Answer 20

1 N converted to 1 P, one electron released

atomic mass unchanged, atomic number increased by 1

Question 21

gamma decay

Answer 21

no particles ejected, high energy photon released

nothing changes

Question 22

decay process

Answer 22

start with unstable parent form and stop when stable daughter is reached

Question 23

what is a closed system

Answer 23

no parent or daughter can be introduced or escape from the crystal

Question 24

what is outgrowth

Answer 24

reduction of parent atom

Question 25

ingrowth

Answer 25

increase of daughter atoms

Question 26

decay equation

Answer 26

quantity that remains = initial quantity of substance that will decay x Euler number ^ - decay constant * time elapsed since system closure

Question 27

what is the most common mineral for uranium lead systems

Answer 27

zircon

Question 28

why is zircon good

Answer 28

• found in most igneous rocks
• hard and resistant to weathering
• resistant to hugh temperatures and metamorphism
• excludes lead during formation
• three dating systems (lead/lead age)

Question 28

radiometric dating limitations

Answer 28

1) not possible to date sediments
- dating original sediments
2) weathering
- leach out isotopes compromising closed system
3) metamorphism
- temperature above which mineral becomes leaky and open system is called closure
- if some daughter products escape, mineral appears younger than it is
- zircon closure is 900c

Question 29

dating with volcanic ash

Answer 29

rapidly cooing and ejected from volcano like bottle of coke after shakes

ash layers contain zircon to date