2. The great detective science Flashcards
What is sandstone useful/not useful for teaching us?
Useful: indicator of depositional environment
Not useful: Usually few fossils and chemical clues.
Why is limestone useful for teaching us about the past?
Many chemical clues (created from remains of shelly creatures), can often have high levels of fossils (but varies vastly)
What makes siltstone, mudstone, and shale useful in teaching us about the past?
Varying amounts of fossils, but generally very fossiliferous.
Chemically diverse, lots of chemical clues.
Forms in gentle water environments - so indicators of depositional environment.
Why is ooze useful for learning about the past in theory - but in practice doesn’t help us much?
Mostly composed of microfossils so has many chemical forensic clues - and is an indicator of deep sea deposition.
- But most old ocean crust is lost to subduction so hard to find ooze to study.
Where is the most useful evidence about the past found? Where is it not?
- Depositional sediment areas; low ground, marine, subsiding basins, continental margins.
- NOT high ground or glaciated regions because of poor survivorship of sedimentary rocks due to erosion.
- NOT deep sea because it has poor survivorship due to subduction.
What are the two types of date obtained when studying deep time?
Relative dates - from fossils/palaeomagnetism
Absolute dates - from radioactive dating e.g. potassium -> argon dating (potassium decaying to argon)
What makes a good indicator fossil? What is one example?
Abundant, easily preserved, widespread, independent of depositional environment, short duration, extinct everywhere at once.
e.g. graptolites
What is rubisco?
The most abundant enzyme on Earth, used by all photo-synthesisers
How is rubisco used to evidence life through rocks?
Rubisco latches onto carbon, and favours carbon 12.
Therefore, a deficiency in carbon 13 within a rock, relevant to the expected ratio with carbon 12, suggests the rock was formed in the presence of rubisco (and hence life).
Why do we need to rely on compounds like rubisco to tell us about early life?
Most early life was soft so can’t really be seen in a fossil record.
What is the significance of studying whether iron is of the form Fe2 or Fe3?
Fe3 iron is oxidised and provides evidence (usually) of an oxygen present atmosphere
What is the Signor-Lips effect?
True duration of a species is longer than fossil duration due to first and last fossils unlikely to be found.
Why is studying DNA useful?
DNA in dated rocks can evidence existence of a species 1000s of years past the last dated fossil.
Why can DNA in sediment be unreliable?
Suggested possibility of DNA leaching through sediment levels to give unreliable results.
How is DNA used with fossils?
DNA can be studied in combination with fossils to estimate population decline rates.
