Planet Surfaces

Question 1

impact velocity equation

Answer 1

v² = v꜀² + vₑ²
vₑ: escape velocity
v꜀: velocity of smaller body relative to larger body#
v: impact velocity

Question 2

what happens to the kinetic energy of an impactor

Answer 2

1. converted to heat on impact
2. vaporises the impactor
3. excavates a crater 20-30 times the impactor’s size

Question 3

crater morphology (micro - large)

Answer 3

micro crater: from high-speed dust particles

simple crater: <18km diameter. paraboloidal shape. (size for moon)
(small)

complex crater: flat-bottomed with a central peak
(large)

Question 4

crater morphology (rings)

Answer 4

peak-ring crater: >100km diameter. has peak rings up to half the total diameter

Multi-ring basin: >300km diameter. has 2 or more concentric ridges facing the centre

Question 5

whats the approximate size difference for different crater morphologies on the moon and earth

Answer 5

on earth they would be 5x smaller

Question 6

what’s crater counting

Answer 6

by counting the number of impact craters in a given area you can determine the relative age of other areas of the same size. the more craters the older the area.

Question 7

decay constant equation

Answer 7

λ= ln(2) / t₀.₅
t₀.₅: half-life

Question 8

number of daughter nuclei equation

Answer 8

given that Nₐ = Nₐ,₀ * e^(-λt)

N꜀ -N꜀,₀ = (e^(λt) - 1)Nₐ

Nₐ,₀ is the initial number of radioactive nuclei
N꜀ is the current number of daughter nuclei

Question 9

different types of isotope clocks

Answer 9

decay clock:
when the initial number of radioactive nuclei is known.
uses Nₐ = Nₐ,₀ * e^(-λt)

accumulation clock:
when the initial number of daughter nuclei is 0
N꜀ = (e^(λt) - 1)Nₐ is used (N꜀ : current number of daughter nuclei, Nₐ current number of parent nuclei)

Isochron clock:
when the initial number of both the daughter and parent nuclei is unknown. Requires multiple Nₐ and N꜀ measurements from rocks of the same age

Question 10

how long is C-14 dating good for

Answer 10

about 50 kyrs

Question 11

how does C-14 dating work

Answer 11

decay clock

1. cosmic rays hit atoms in the upper atmosphere, producing neutrons that interact with nitrogen to form C-14
2. living organisms maintain a constant C-13 / C-14 ratio as carbon is taken in. when they die the stop taking carbon in so it can change through decay

Question 12

How does K-Ar dating work

Answer 12

Accumulation clock
used for dating igneous rock.

1. K-40 decays into Ar-40. Gaseous Ar-40 is assumed to have an initial value of 0 since it could escape the molten rock
2. when the rock solidifies K-40 starts to decay and the Ar-40 can’t escape.

Question 13

How does Rb-Sr dating work

Answer 13

Isochron clock

1. N꜀ -N꜀,₀ = (e^(λt) - 1)Nₐ is used. The number of the chemically stable isotope of the daughter nuclei N(sub c) (N꜀ should be sub b).
2. Compare to y = mx+c. y = N꜀/N(sub c) and x = Nₐ/N(sub c)
3. multiple measurements of Nₐ and N꜀ are taken in the same area (so t is approximately constant) and an x-y graph is plotted. The gradient is used to find t