Lesson 9) Statigraphy and Geologic Time Flashcards
Statisgraphic concepts and the scale of Earth History
Principle of Superposition
Tendency or rock layers to be chronologically stacked.
- Sediments deposited -> gradual build up
- How things normally work, but can be exceptions:.
Unconformity
Flat surface caused by partially melted igneous intrusions that are uplifted and eroded
Statigraphy
Science of using arrangement and composition of rock layers to interpret geological history
Formation
Large uninterrupted sequence of rock that is made of multiple layers that all share similar properties (eg- composition + grain size) all formed under similar conditions
What is indicated when a rock changes formations?
Large scale change occurred in the environment where the rocks were deposited.
Principle of Superposition
Allows stratigraphies to infer relative age of rock layers (layer age vs other layer age)
- DOES NOT determine absolute age
Radiometric dating
Technique to determine rocks age.
As rock ages, isotopes decay and ratio of isotopes : decay product decreases.
Mass spectrometers can measure the isotope ratio of rock, which can tell how old it is.
Isotope
Variant of a chemicalelement that has unusual number of neutrons.
- some are unstable and undergo radioactive decay: energy release, resulting in atoms w/ different compositions (decay products)
What rock can’t be radiometrically dated?
Sedimentary
They are not new: they are made of sediments that have already formed and are undergoing radioactive decay already probably.
However: can use volvanic ash layers (within sedimentaries to estimate nearby fossil ages)
What can usually be radiometrically dated?
Igneous
Formed anew
- When igneous rock solidifies, it starts out w/ isotope ratio equal to that found in its environment
How can we measure fossils age, if they’re usually found in sedimentary rocks?
Radiometric dating + principle of superstition
IF found between two horizontally deposited igneous rock layers— can bracket age
Geologic Time Scale
Standardized series of chronological divisions that parses Earth’s history into discrete named units.
Eons > Eras > Periods > Epochs
Hadean eon
4.4-4 billions yrs ago
Formation and earl Earth years.
- Surface partially molten and hella volcanoes
- Planet collision which formed moon
By then end, Earth had cooled and hella oceans
- organic molecules form
Archean Eon
2-2.5 billion yrs ago
- Oldest fossils (single-celled organisms)
- Cynanobacteria made oxygen and stromatolites
Stromatolites
Structures formed by cyanobacteria from the Archean Eon
- Lump stones that when cut in half, show layers of secreted sticky limbs trapping sediment particles.
Proterozoic Eon
2.5 billion-541 million years ago
- FIrst multicellular organisms
- very poor fossil record as life at this point was BONELESS
Ediacarian period: Large forms of life (like animals) finally got here bruh
Phanerozoic Eon
540-0 millions years ago
Subdivided into 3 eras
- Rapid animal evolution
Paleozoic Era
541-252mil years ago
- Primitive ocean-dwelling invertebrates (me fr)
- Big ass forests w/ reptiles, amphibians, insects
Cambrian Period
541-485 mil years ago
- Aquatic life diversification (Cambrian explosion)
- Anomacolaris, arthropods, SpongeBob worms etc
Ordovician Period
485-443 mil years ago
- OCEAN ANIMALS RULE!!!!
Silurian Period
443-419mil years ago
- predator fish get jaws #looksmaxing
- land plants start flourishing
- millipede anthropods start crawling on ocean floor
Devonian Period
419-359 mil years ago
- FIrst forests EVOR!!!
- sharks
- the fishies start venturing onto land
Carboniferous Period
359-299 mil years ago
- ambhipians swamps and reptiles
Permian Period
299-252 mil years ago
- PANGAEA FORMS!!!
- Reptiles evolve into 3 linages which make up every major animal
Mesozoic Era
252 - 66 mil years ago
“Age of Dinosaurs”
- Marine reptiles evolve (first true reptiles, mammals, birds)
- First flowering plants
Cenozoic Era and its 3 periods
66-0 mil years ago
“Age of Mammals”
- Grass reveal
Periodt!!!
1. Paleocene: 66-23 mil
- Cooling temperatures, mammals + birds diversifying
2. Neogene: 23-2.6mil
- HOMINIDS IN AFRICA
3. Quaternary: 2.6-0 mil
- Ice age
- First anatomically modern humans and civilization
Triassic Period
252-201 mil years ago
- Life slowly recovers from mass extinction of Permian era
- first mammals and Dino’s evolve
- Pangaea breaks apart
- Ichthyosaurs + Plesiosaurs = Pterosaurs
Dinosaurs of the Triassic Period?
First Ornithischians:
- Pisanosaurus
First Theropods:
- Herrerasaurus
- Eoraptor
First sauropodomporphs:
- Panphagia
Prosaurupods:
- Plateosaurus
Ichthyosaurs
“Fish Lizard” but aren’t lizards (nor fish)
Group of reptiles that took on a fish-like lifestyle and evolved a very fish body form (and returning to sea)
- Ancestors: Terrestrial reptiles
- Paddle-like front + hind limbs, fin tail, dorsal fin
- Long snout w/ conical teeth (piscovore)
- BUT: never evolved gills so they still needed to breath air
Plesiosaurs
Group of reptiles that a loved secondarily aquatic lifestyle
- Large chests + torsos
- Broad, paddle iambs
- Short tails
- Vary in front
eg) elasmosaurus (keep in mind it lived in Cretaceous period)
Pterosaurs
Close relatives of dinosaurs who branched off reptilian family tree at roughly the same time dinosaurs did
- FIRST FLYERS
- Membranous wings supported by elongated
Jurassic Period
201-145mil years ago
Dino diversification
- Sauropods were dominant terrestrial herbivores
- small ornithopods
- theropods were dominant terrestrial carnivores
- rhamphorhynchoids and pterodactyloids
- first birds
- first ankylosaurs and ceratopsians (but not diverse yet)
Rhamphorhynchoids
Early pterosaurs
eg) stegosaurus
Pterodactyloids
Came from ramphorhynchoids, differing in morphology
- short tails
- elongated carpels which made wings longer
- large head crests as display
- ranged in size
eg) pteranodon
Early Cretaceous Period
146-100 mil years ago
- first flowers
- spinosaurids and charcharodontosaurids
- coelurosaurian theropods diversify
- iguanodonts get big and many – sauropods decline
- Mosasaurs
- stegosaurs get replaced by ankylosaurs
- primitive birds abundant (better than archaeopteryx)
Mosasaurs
Relatives of modern monitor lizards and snakes
- reptiles
- tail finds and paddle limbs
- BUT bodies were longer than ichthyosaurs and plesiosaurs
- most were predatory and big
Late Cretaceous Period
100-65 mil years ago
- all the famous celebrity Dino’s
- coelurosaurian theropods abundant and diverse
- ankylosaurs diverge into two: ankylosaurids and clubless nodosaurids
- Ceratopsians and hadrosaurs are dominant herbivores (northern)
- titanosaurid sauropods are dominant herbivores (southern)
- pachycephalosaurs!!!
- flower plants evolve <3
- THEN THEY ALL DIE!!!! MASS EXTINCTION!!!!!
What were some coelurosaurian theropods that lived
Tyrannosaurs, oviraptorosaurs, dromaeosaurids, oviraptosaurs, therizinosaurs, troodontids
How long ago was the Earth formed?
4.6 billion years ago
