Fossils & Stratigraphy 5.4

Question 1

Uniformitarianism?

Answer 1

The self evident truth that all natural processes & scientific laws are the same throughout time & the universe.

Question 2

Superposition?

Answer 2

The older layers are always beneath the new/younger layers

Question 3

Stratigraphy?

Answer 3

Study of strata in rocks

Question 4

Relative Dating?

Answer 4

Determining the age of a layer by comparing it with the above layer and below layer.

Question 5

Fossils and how they form? (4 types)

Answer 5

Casts & Moulds

• hard shells, bones preserved in sediments but slowly dissolve leaving a mould
• if cavity fills it becomes cast

Carbonisation

• Tissues of organism chemically changed to carbon-rich material like coal
• Common for plants

Mineralisation

• Minerals precipitate into hollow parts of fossil > hardening it e.g. petrified wood
• Mineralisation can occur in tiny spaces (hollow cells) like plant veins > detailed fossil

Replacement
-Hard parts of organism dissolved by water chemicals & replaced by minerals

Question 6

Index Fossils?

Answer 6

-Fossils or organism which lived in many places throughout Earth but flourished for short time
-Many are microscopic plankton with silica skeletons
-remains are widespread in sediments from a particular time & instantly recognisable
-presence of index fossils tells us where in history we’re looking at:
above it = younger
below it = older

Question 7

What can we conclude from Index Fossils?

Answer 7

Using stratigraphy & absolute dating we find:

• end of snowball earth =(same time) first Ediacaran fossils
• Oxidation of sediments increased 15% - 20% FAST = perfect amount for larger animals to function well
• Maybe global warming > more algae photosynthesis > releasing more Oxygen
• at some point evolution of larger, oxygen dependant animals became possible: Ediacarans arise!
• End of snowball earth = tectonic rifting and volcanic activity > releasing C02 and causing global warming
• Rifting at MOR = concentrations of Calcium ions in oceans to rise > calcium ions essential for skeleton & shells to evolve

Question 8

Extinction?

Answer 8

• When 30% or more species world-wide become extinct within 2 my or less
• Detected by counting number of types of living things found as fossils in rocks from each period in history
• info needed from all global fossil sites
• When types are graphed against time > mass extinctions shown as sudden large dips in graph

Question 9

Mass Extinctions & The Geological Time Scale

Answer 9

• 2 mass extinctions correspond to division on Phanerozoic Eon
• Major mass extinctions are the divide between periods
• mass extinction divided Ordovician & Silurian periods of the Palaeozoic Era

Question 10

The End-Permian Extinction?

Answer 10

Marks division between Palaeozoic & Mesozoic Eras (95% earth species became extinct)

Question 11

Evidence of End-Permian Extinction?

Answer 11

• Fossil studies > 95% extinct over 2-3 phases over 1-2 mys
• Sedimentary layers show big drop in sea levels followed by big rise
• Volcanic lava structures in Siberia date from this time > total amount of lava could bury earth 10m deep

Question 12

Hypothesis of End-Permian Extinction?

Answer 12

• resulted from climate changes induced by huge volcanoes over 60 thousand years
  1. dust/ash caused cooling > ice caps > lea levels drop > Marine life in shallow seas died out

2. so much C02 in atmosphere > greenhouse global warming occurred > ice melted, sea levels rise > oceans made anoxic by rotting of dead materials > made acidic by dissolved C02 & volcanic gases