Stratigraphy & Geologic Time

Question 1

Principle of Superposition

Answer 1

Tendency for rock layers to be chronologically stacked.

Oldest rocks from oldest deposited sediments at the BOTTOM.
Layers become increasingly younger towards the top.

Question 2

Exceptions to the Principle of Superposition

Answer 2

Igneous rock may cut vertically through the horizontal layers.

Mountain building events may tilt, fold & flip rock layers.

Question 3

Stratigraphy

Answer 3

Science of using the arrangement & composition of rock layers to interpret geological history.

Question 4

Formation

Answer 4

Large uninterrupted sequence of rock that is made up of multiple layers that all share similar properties & that all formed under similar conditions.

Question 5

How do we determine absolute age of rock layers?

Answer 5

Radiometric dating - as isotopes decay & ratio of isotopes to decay products deacreases, use mass spectrometer to measure ratio & tell how long ago it formed.

Question 6

Isotopes

Answer 6

variant of a chemical elements that has an unusual number of neutrons.

Question 7

Which rocks cannot be accurately dated with radiometrics?

Answer 7

Sedimentary rocks - formed of pre-existing sediments

Question 8

Which rocks are perfect for radiometric dating?

Answer 8

Igneous rocks - formed new.

Also, volcanic ash!

Question 9

How can we use Igneous rocks to get date range for sedimentary rocks?

Answer 9

Dating igneous above and below the sediments tells us the range

Question 10

Geological Time Scale

Answer 10

Standardized series of chronological divisions that parses the Earth’s history into discrete named units.

Largest <—————-> Smallest

Eons Eras Periods Epochs

Question 11

Hadeon Eon

Answer 11

4.6 - 4 billion years ago

Moon ~4.5 bil yrs ago

Large oceans covered surface

Complex organic molecules formed in oceans & were prob earliest true life forms.

Oldest dated ROCKS from here @ ~4.4 bil yrs ago.

Question 12

Archean Eon

Answer 12

4 - 2.5 bil yrs ago

oldest known FOSSILS from here of single celled organisms

Cyanobacteria: Photosynthetic & produced large amounts of oxygen gas that became concentrated in Earth’s atmosphere.

Stromatolites: Cyanobacteria formed these structures. Best early records of life. Look like lumpy stones & when cut in half cans ee layers created as cyano secreted sticky films that trapped sediment.

Question 13

Proterozoic Eon

Answer 13

2.5b - 541 million yrs ago

~1.7 nillion yrs ago, first multicellular organisms evolved. No bones / hard structures & were generally microscopic, so poor fossil record.

Edicarian Period: ~630 - 541 mil yrs ago, large forms of life w/ some harder parts evolved, including first animal life!

Question 14

Phanerozoic Eon

Answer 14

541 - 0 million years ago.

3 Eras, each w/ many Periods.

Animal life rapidly evolved into a multitude of diverse forms, including dinos.

Includes Paleozoic Era (primitive invertebrates & forests w/ reptiles and whatnot), Mesozoic Era (‘Age of Dinos’) and Cenozoic Era (post-dinos to us, ‘age of mammals’).

Question 15

Paleozoic Era

Answer 15

541 - 252 million years ago

primitive invertebrates in oceans, great forests w/ insects, amphibians and reptiles.

Includes Cambrian period, Ordovician Period, Silurian Period, Devonian Period, Carboniferous Period & Permian Period.

Question 16

Cambrian Period

Answer 16

541 - 485 million years ago

Cambrian Explosion - Dramatic diversification of aquatic life @ beginning of Cambrian. Sponges, molluscs, worms, arthopods (trilos) evolved.

Pikaia - early relative of vertebrates. No vertebrae but many other features.

Question 17

Ordovician Period

Answer 17

485 - 443 million yrs ago

High sea levels

Oceans continued to diversify, fish increasingly becoming dominant large aquatic animals.

Question 18

Silurian Period

Answer 18

443 - 419 million years ago

Fish evolve jaws & large predatory fish evolve.

Primitive plant life began to flourish on land.

Question 19

Devonian Period

Answer 19

419 - 359 million years ago

First forests on land

Huge jawed fishes like Dunkleosteus (second strongest bite ever, behind T.Rex) & first true sharks.

Lobe finned ‘fishapods’ like Tiktalik ventured onto land & gave rise to tetrapods.

Question 20

Carboniferous Period

Answer 20

359 - 299 million yrs ago

Amphibians abundant in swamps

Reptiles (first amniotes!) evolved

Todays coal is from Carboniferous rotting swamps

Question 21

Permian Period

Answer 21

299 - 252 million yrs ago

Continents collide & form PANGAEA

Reptiles evolve 3 main lineages: Anapsids (turtles), Synapsids (mammals), & Diapsids (crocs, lizards, snakes & DINOS).

Rocks from this Period are arid, dry desert environments.

End Permian Extinction Event - single greatest mass extinction in history. All trilos dead :(

Question 22

Mesozoic Era

Answer 22

252 - 66 million years ago

Age of Dinos - dinos evolve & become dominant form of terrestrial life.

Marine reptiles, like Ichtyosaurs, Plesiosaurs & Mosasaurs evolve.

First true crocs, turtles, lizards, snakes, mammals & birds evolve.

First flowering plants evolve by end Mesozoic.

Includes Triassic, Jurassic & Cretaceous Periods.

Question 23

Cenozoic Era

Answer 23

66 - 0 million years ago

Age of mammals - extinction of dinos allowed mammals to evolve larger forms & fill those ecological roles.

Grasses abundant.

Includes Palogene period, Neogene period, Quaternary period.

Question 24

Palogene Period

Answer 24

66 - 23 mil yrs ago

global temps began to cool

mammals diversify (primates, bats, whales, etc.)

Birds Diversify.

Question 25

Neogene Period

Answer 25

23 - 2.6 million years ago Global temps continue to cool First hominids evolve in Africa.

Question 26

Quaternary Period

Answer 26

2.6 - 0 million years ago Earth experiences many 'ice ages' Humans evolve & civilization spreads

Question 27

How long did non-avian dinos exist?

Answer 27

For 135 million years. Less time separating first humans to last dinos than the last dinos to the first dinos.

Question 28

Triassic Period

Answer 28

252 - 201 million years ago Pangaea beings to break apart. First ornithiscians (Psianosaurus), Theropods (Eoraptor & Herrerasaurus), & sauropodomorphs (Panphagia) were all SMALL & BIPEDAL. Prosauropods (i.e. Plateosaurus) were first large herbivorous dinos. First Ichthyosaurs ('fish lizard' but not lizards nor fish). Reptiles whose ancestors were fully terrestrial & they found success by making evolutionary return to water. Evolved paddle-like front & hindlimbs, finned tail & shark-like dorsal fin. Long snouts w/ conical teeth - psicivores. Never evolved gills. Plesiosaurs - Large chests & torsos, broad paddle-shaped limbs & relatively short tails. Above shoulders varied tremendously. Pterosaurs - close relatives of dinosaurs, branched off of reptiles @ roughly same time as dinos. First vertebrates to fly. Have membranous wings supported by single extremely elongated finger. Early ones belonged to rhamporhynchoids.

Question 29

Jurassic Period

Answer 29

201 - 145 million yrs ago Dinos diversified, peak sauropod diversity. small & medium ornithopods were common non-coelurosaurian theropods like Allosaurus were dominant terrestrial carnivores. Stegosaurs almost completely restricted to jurassic. first ankylosaurs, ornithopods & ceratopsians appear and first birds evolve (Archaeopteryx). Morrision Formation USA & Solnhofen Germany best fossil records of Jurassic. Pterodactyloids evolve from Rhamphorahynchoid pterosaurs. Have shorter tails & elongated carpals in their wrists (longer wings). Large head crests (display structures). Could be small (robin size) or over 10m wingspans (largest ever flying creatures).

Question 30

Early Cretaceous

Answer 30

146 - 100 million years ago. First flowering plants New theropods (i.e. Spinosaurids & Carcharodontsaurids) evolve & coelurosaurian theropods become more diverse. Iguanodonts become larger & more abundant. Yixian Formation China, Wealden Supergroup England & Cedar Mountain Formation Utah were important early creataceous fossil units. Mosasaurs - Relatives of modern lizards and snakes. Tail fins & limbs modified into paddles, bodies & tails elongate. Some over 18m long. Seem adapted to deep-sea & big-game hunting.

Question 31

Late Cretaceous

Answer 31

100 - 65 million years ago Apex of non-Avian dino diversity (most famous dinos from here). Coelurosaurians theropods (tyrannosaurids, ornithomimids, therizinosaurs, oviraptorosaurs, dromaeosaurs, troodontids) diverse in NORTHERN hemisphere. Snkylosaurs diverge into ankylosaurids (tail-clubbed) & nodosaurids (non-tail clubbed). Ceratopsians & Hadrosaurs are dominant large herbivores in norther hemisphere. Only single sauropod lineage remaining are titanosaurids, dominant herbivores in southern hemisphere. Pachycephalosaurs ONLY known from late cretaceous. End cretaceous - big meteor collides w/ earth leading to extinction of all non-avian Dinos.