9: Stratigraphy and Geologic Flashcards
Principle of Superposition
tendency for rock layers to be chronologically stacked
Stratigraphy
the science of using the arrangement and composition of rock layers to interpret geological history
formation
a large uninterrupted sequence of rock that is made of multiple layers that all share similar properties (ex. mineral composition) and that all formed under similar conditions
radiometric dating
to age rocks in absolute terms
use mass spectrometer
measure isotop: decay product ratio
can’t use sedimentary rocks, use igneous rocks instead and volcanic ash deposits
Isotopes
a variant of a chemical element that has an unusual number of neutrons
some are unstable and will undergo radioactive decay, whereby energy is released and a new atom with a different composition of particles results (decay products)
a large collection of isotopes will radioactively decay at a mathematically predictable rate
The Geologic time scale
a standardized series of chronological divisions that parses the Earth’s history into discrete named units
Largest units to smallest are: Eons, Eras, Periods, Epochs
Hadean eon
4.6-4 BYA
earth surface partially molten and widespread volcanic activity
4.5 bya earth collided with smaller planetoid, which led to the formation of the moon
by the end of the eon, the earth had cooled, large oceans covered the surface
Complex organic molecules are said to have formed in these early oceans
Archean Eon
4-2.5 BYA
oldest known fossils (single-celled organisms)
Cyanobacteria > led to oxygen production which became concentrated in earth’s atmosphere
Stromatolites (records of early life)
Proterozoic Eon
- 5 BYA - 541 MYA
- 7 BYA = first multicellular organism (no bones)
Ediacaran Period: 630-542 MYA large forms of life with hard parts > first animal life
Phanerozoic Eon
541-0 MYA
3 eras (Paleozoic, Mesozoic, cenozoic)
animal life evolved rapidly, including dinosaurs
Paleozoic Era
541-252 MYA
primitive invertebrates living in oceans > forests covering land and land teamed with reptiles, amphibians, and insects
Periods: Cambrian, ordovician, silurian, devonian, carboniferous, permian
Cambrian period
541-485 MYA
dramatic diversification of aquatic life
Cambrian explosion
sponges, molluscs, worms, anthropods (trilobites)
Ordovician Period
485-443 MYA
global sea levels were high
life in oceans diversify
fish increasingly become dominant large aquatic animals
Silurian period
443-419 MYA
evolution of jaws in fish
primitive plant life began to flourish
Devonian period
419-359 MYA first forests appeared on land hige jawed fish first true sharks appeared lobe finned fishapods ventured onto land > tetrapods
Carboniferous period
359-299 MYA Amphibians widespread in the abundant swamps insects evolve flight reptiles (the first amniotes) evolved coal mined today is from these swamps
Permian Periods
299-252 MYA
continents collided = Pangea
reptiles evolved into 3 lineages: anapsids, synapsids, diapsids.
dry desert environment
single greatest mass extinction in planet’s history took place at the end of this period, one of the major losses was the trilobites
Mesozoic Era
252-66 MYA
Age of dinosaurs
dinosaurs evolved and became dominant form of large terrestrial life
many marine replies evolve (ichthyosaurs, plesiosaurs, mosasaurs)
first true turtles, crocodilians, lizards, snakes,, mammals, and birds evolved at this time
Angiosperms
periods: triassic, jurassic, cretaceous
Cenozoic era
66-0 MYA
Age of Mammals
the extinction of dinosaurs allowed mammals to evolve and thrive
Grasses become abundant
periods: paleogene, neogene, quartenary gene
Paleogene period
66-23 MYA
global temperatures cool
mammals diversified into a variety of new forms (primates, bats, whales)
birds diversified
Neogene period
23-2.6 MYA
global temperatures cool
first Hominids evolved in africa
Quarternary period
2.6-0 MYA
several ice age events
first anatomically modern humans evolved
human civilization spread
Triassic Period
252-201 MYA
life recovered from Permian mass extinction
first mammals and dinosaurs and pterosaurs evolved near the end of this period
Pangea begins to fall apart
Ornithichians, theropods, sauropodomorphs: small and bipedal
Ichtyosaurs evolved
Pleiosaurs evolved
Ichtyosaurs
group of lizards that look like fish triassic period found evolutionary success by returning to water piscivores no gills
Pleiosaurs
Triassic
reptiles that returned to aquatic lifestyle
large chests, paddle shaped limbs
short tails
Pterosaurs
Triassic
close relatives of dinosaurs, branched off from the reptilian family tree at around the same time as the dinosaurs did
first vertebrates to fly
membranous wings supported by a single extremely elongated finger
Rhamphorhynchoids
group where early pterosaurs belong
Jurassic period
201-145 MYA
dinosaurs diversified
peak sauropod diversity, dominant terrestrial herbivores
small/medium ornithopods
non-coelurosaurian theropods were dominant terrestrial carnivores
stegosaurs restricted to jurassic
first ankylosaurs/ornithppods/ceratopsians appear (but are not diverse or abundant yet)
First birds evolved
Rhamphorhynchoids pterosaurs gave rise to new pterosaur group > pterodactyloids
pterodactyloids
group of pterosaurs jurassic differ from Rhamphorhynchoids in morphology of their tails (which were short) and their carpels (which were elongated, leading to greater wing length). had large head crests largest animals to ever fly
Early Cretaceous period
146-100 MYA
First flowing plants evolved
dinosaurs continue to diversify
new theropods evolve
coelurosaurian theropods become more diverse
iguanodonts become larger and more abundant
Mosasaurs
Mosasours
Cretaceous period
third major reptilian group began patrolling waters
relatives of modern monitor lizards and snakes
tail fins
limbs modified into paddles
elongate bodies and tails
preyed on fish and other marine reptiles
Late cretaceous period
100-65 MYA
apex of non-avian dinosaur diversity
coelurosaurian theropods abundant/diverse in northern hemisphere (tyrannosaurs, ornithomimids…)
ankylosaurs have diverged into two groups: tail-club ankylosaurids and the clueless nodosaurids
ceratopsians and hadrosaurs: dominant large herbivores in large hemisphere
only single sauropod lineage remains, dominant herbivores in southern hemisphere
pachycephalosaurs only known here
cretaceous mass extinction
