The Great Detective Science

Question 1

Why is reconstructing the Earth’s History called ‘the Great Detective Science’

Answer 1

Little of the evidnece is straightforward to interpret, because it is old, squashed, altered, and in code

Question 2

What two methods are coming together to help piece together the Earth’s history

Answer 2

The field has mature (geology, fossils) and immature (DNA, biomarkers) methods, increasingly forming a powerful combination

Question 3

Where is Sandstone predominatly found

Answer 3

Desert, Coastal Dunes, Growing delta, River channels

Question 4

Describe Sandstone

Answer 4

Grains mostly quartz, various cements
Metamorphoses to quartzite if pure
Usually few fossils (moderate to high energy)
Few chemical forensic clues

Question 5

Where is Limestone predominatly found

Answer 5

Nearshore, lagoon, reef
Deep sea

Question 6

Describe Limestone

Answer 6

Grains and cement mostly CaCO₃ (Mg⁺)
Metamorphoses to marble if pure
Few to many to all fossils
Many chemical forensic clues

Question 7

Where are Siltstone, mudsone and shale predominatly found

Answer 7

Quiet, gentle environments
Lakes, Lagoons
Far continetal shelf, slope, deep margin
Deep sea

Question 8

Describe Siltstone, mudstone and shale

Answer 8

Grains mostly quartz, various fines and cements
Metamorphoses to slate then schist then gneiss
Few to many fossils
Many chemical forensic clues

Question 9

Where is Ooze (and Red Clay) predominatly found

Answer 9

Deep sea
Where fossils are rare, mostly windblown dust; red clay

Question 10

Describe Ooze

Answer 10

Brains mostly microfossils: CaCO₃ or silica
Rarely found metamorphosed (subducted)
Mostly microfossils
Many chemcial foresic clues

Question 11

Why is fossil evidence not found on high ground

Answer 11

Because it will experience high erosion and weathering

Question 12

Why is fossil evidence found in low ground and marine (low basins, contiental margins etc)

Answer 12

Good chances of deposition and long-term survival with physical and chemical integrity

Question 13

Why is fossil evidence found on oceanic crust

Answer 13

It has a good chance of deposition
However there is issues with its long term survival

Question 14

Where hence are the best places to find fossils

Answer 14

Deep sea
Continental margins
Subsiding basin
Delta (moderate to good)
Lake, Swap and channel (moderate to good)
Palaeosol (=fossil soil) (moderate)
Desert (moderate)

Question 15

Tradiditonal environmental reconstruction is from

Answer 15

Grain characterisitcs, rock structures and fossils

Question 16

How can the K-Ar ratio be used to give the age of volcanic rock

Answer 16

When a volcanic rock solidifies, it contains K with no appreciable Ar
K decay to Ar at a rate known to physicits (~1.2 By)
This is unaffected by heat or pressure
Ar can escape and contamination can be a good problem, so care and good sample selection needed

Question 17

What are characterisitc of good ‘marker’ fossil

Answer 17

• Abundant
• Good preservation potential) organisms with hard parts
• Widespread (global)
• Lives/winds up depsotied in different environments - planktonic graptolites idea
• Appears and become abundant and widespread quickly
• Extinct everywhere at once quickly, preferably not at a mass extinction boundary
• Short duration

Question 18

Didymograptus leintwardinensis once existed in the sea, floating passively near the surface
Very abundant and widespread, so found in many types of marine rock nearly everywhere
Died out, cause unknown, everywhere at the same time
How can this be used in relative dating

Answer 18

Rocks containing D.leintwardinensis everywhere are all the same age; lower rocks are older and higher rocks are yonger

Question 18

Rubisco can be used as a biomarker
What is it main biological use

Answer 18

All photosynthesisers use rubisco to make carbon compounds
It is the most abundant enzyme on earth, which in involved in the first major step of carbon fixation, through catalysing a reaction between carbon dioxide and RuBP

Question 19

If something is an inorganic carbon compound
What it it’s basic formula going to be

Answer 19

CH₂O

Question 20

What is an inorganic carbon compound

Answer 20

Something that can be precipitated by some living things in the form of, for example, shells
e.g. CaCO₃

Question 21

If a record said “Δ ¹³C of -20%”
What does this mean

Answer 21

Deficient in ¹³C to the tune of 20%
Relative to typical carbonate carbon ratio

Question 22

If the carbon compounds in a rock have a Δ ¹³C of -20%, what has caused this?

Answer 22

The most likely explanation is that the compound was made using rubisco, which means photosynthesis and life

Question 23

Why do we predominatly look at isotopes in rocks when analysing early life

Answer 23

Because early life was soft bodied and hence would not fossilise well

Question 24

The Carbon + Rubisco signature is one example of fractionation:
What is this?

Answer 24

Some process that distorts the ratios of elements or chemicals away from their otherwise expected values
Many elements have isotopes that are fractionated away from their expected values by one process or set of conditions or another

Question 25

How can iron be used as a chemical indicator or the environment and early life

Answer 25

Much Iron is in rocks and its oxidation state gives us clues about the oxidation state if the environment of deposition (if oxygen was around or not)

Question 26

Why are biomarkers a useful way to learn about early life

Answer 26

Biomarkers have great potential to tell us things we want to know. Different groups of lifeforms produce different organic compounds as end or intermediate products
We can now measure organic compounds present in rocks in minuscule amounts - using gas chromatography mass spec

Question 27

What is the problem with biomarkers however

Answer 27

Other scientists have pointed out that compounds could have migrated into the focal rock from younger ones

Question 28

How can comparision of genes be used to look at evolutionary relationships

Answer 28

The more similar the genetic code between current living organisms and ones previously lived
Differences between codes can be converted to estimates of times of divergence: so-called ‘molecular clock’ estimates
Molecular clock analyses must be ‘tied down’ by fossil evdience to be worth much

Question 29

What is the Signor-Lipps effect

Answer 29

since the fossil record of organisms is never complete, neither the first nor the last organisms in a given taxon will be recorded as a fossil
The Signor-Lipps effect is often applied specifically to cases of the youngest-known fossils of a taxon failing to represent the last appearance of an organsism
But overall its hard to know the full life-time of a species because of this