CHAPTER 9 Flashcards
sediments
sedimentary rocks form from small organic or inorganic particles called sediments that accumulate and are cemented together.
Principle of Superposition
The tendency for rock layers to be chronologically stacked is called the Principle of Superposition.
where do igneous rocks form from?
Igneous rocks that form from volcanic activity may vertically cut through horizontally arranged layers of rocks, and mountain building events may tilt, fold, and even flip rock layers.
Stratigraphy
Stratigraphy is 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 (such as mineral composition and average sediment grain size) and that all formed under similar conditions is termed a formation
When a sequence of rock changes from one formation to another, what does it indicate?
it indicates that a large scale change occurred in the environment where the rocks were being deposited.
The Principle of Superposition allows a stratigrapher to
to infer the relative age of rock layers (that is, how old one layer is relative to another), but it does not determine the absolute age (that is, how old in years the layers are).
To age rocks in absolute terms, a technique called _______ _____ is used.
radiometric dating
isotope
a variant of a chemical element that has an unusual number of neutrons
decay products
Some isotopes are unstable and will undergo radioactive decay, whereby energy is released and a new atom (or atoms) with a different composition of particles results. These resulting atoms with different particle compositions are called the decay products.
When a new rock forms, it has a …
ratio of isotopes and decay products that matches that of the environment.
As the rock ages…
the isotopes decay and the ratio of isotopes to decay products decreases.
mass spectrometer
Using a special machine called a mass spectrometer, it is possible to measure the isotope ratio of a rock, and this ratio can tell you how long ago the rock formed.
why can sedimentary rock usually not be radiometrically dated
Because they are made of sediments that had already formed and that were already potentially undergoing radioactive decay
why can igneous rocks can be radiometrically dated
igneous rocks are formed anew and can usually be radiometrically dated.
if fossils are usually found in sedimentary rocks and not in igneous rocks, how can we ever tell how old a fossil and its rock layer is?
By combining radiometric dating and the principle of superposition. If sedimentary rocks that contain fossils are found between two horizontally deposited layers of igneous rocks, then dating the igneous rocks above the sedimentary layer will tell us what age the fossils must be older than, and dating the igneous rocks below the sedimentary layer will tell us what age the fossils must be younger than. So, we can confidently bracket the age of the fossils.
___________ are a key tool in fossil dating.
Volcanic ash deposits
how are volcanic ash deposits used for dating fossils.
we can be certain that particular particles of igneous rocks that compose the sedimentary rocks that the fossils are buried in were incorporated into the sediment at nearly the same time that they were formed. For instance, fossils may be buried by, or be buried near, deposits of volcanic ash. Volcanic ash forms at the moment of an eruption, and the time between when an eruption occurs and when its ash falls to the surface is inconsequently short.
________ and ________ dating are combined to piece together the history of the earth and to create the geologic time scale.
Stratigraphy and radiometric
The largest units in the time scale are
Eons - Eras - Periods - Epochs
THE HADEAN EON – 4.6 TO 4 BILLION YEARS AGO
- by the beginning of this eon, the rest of the universe was already over nine billion years old
- surface of the earth partially molten and with volcanic activity widespread
- By the end of the Hadean, the earth had cooled and large oceans covered much of its surface. Complex organic molecules are thought to have formed in these early oceans and possibly the earliest true life forms.
how and when was the moon created
in the Hadean Eon and was formed when the earth was at roughly 4.5 billion years ago, the young earth collided with a smaller planetoid. This collision ejected a large mass of debris, which was held in orbit by the earth’s gravity and eventually formed the moon.
THE ARCHEAN EON – 4 TO 2.5 BILLION YEARS AGO
- The oldest known fossils come from the Archean Eon. These fossils are of simple single- celled organisms
- More advanced forms later evolved in the Archean, including cyanobacteria
cyanobacteria
The cyanobacteria were photosynthetic and eventually produced large amounts of oxygen gas, which became concentrated in the earth’s atmosphere. Some cyanobacteria formed structures called stromatolites
stromatolites
some of the best records of early life. Stromatolites look like lumpy stones, but when you cut them in half you can see the layers that were created as the cyanobacteria secreted sticky films that trapped particles of sediment.
THE PROTEROZOIC EON – 2.5 BILLION TO 541 MILLION YEARS AGO
- 1.7 billion years ago, the first multicellular organisms evolved.
- Within the Proterozoic, the time span from 630 to 542 million years ago is known as the Ediacaran Period.
why is the record for early life poor?
Because single-celled and early multicellular life had no bones or other hard parts and was usually microscopic
Ediacaran Period
During the Ediacaran, large forms of life with some harder parts evolved, including the first animal life.
THE PHANEROZOIC EON – 541 TO 0 MILLION YEARS AGO
- The Phanerozoic Eon is subdivided into three eras, which are themselves subdivided into numerous periods
- It is during the Phanerozoic that animal life rapidly evolved into a multitude of diverse forms, including dinosaurs.
The Paleozoic Era – 541 to 252 million years ago
At the start of the Paleozoic, animal life was restricted to primitive invertebrates living in the oceans, but, by its close, great forests covered the land and teamed with reptiles, amphibians, and insects.
The Cambrian Period – 541 to 485 million years ago
- The beginning of the Cambrian marks such a dramatic diversification of aquatic animal life that it is often referred to as The Cambrian Explosion
- A close early relative of the vertebrates, called Pikaia.
Pikaia
didn’t have vertebrae, but had several other features found in vertebrates.
The Ordovician Period – 485 to 443 million years ago
- Global sea levels were high.
- Life in the oceans continued to diversify, with fish increasingly becoming the dominant large aquatic animals.
The Silurian Period – 443 to 419 million years ago
- Until this point, fish had not yet evolved jaws. With the evolution of jaws came the evolution of large predatory fish.
- Primitive plant life began to flourish on land.
The Devonian Period – 419 to 359 million years ago
- The first forests appeared on land.
- Huge jawed fishes, like Dunkleosteus, evolved in the seas, and the first true sharks appeared. Lobe-finned ‘fishapods’, like Tiktaalik, ventured onto land, and give rise to the tetrapods.
The Carboniferous Period – 359 to 299 million years ago
Amphibians were widespread in the abundant swamps, and reptiles, the first amniotes, evolved. Much of the coal that is mined today formed from the rotting plants of Carboniferous swamps.
The Permian Period – 299 to 252
The continents collided together and formed a single super continent called Pangaea. Reptiles evolved into three main lineages:
- Anapsids
- Synapsids
- Diapsids
- The single greatest mass extinction in our planet’s history occurred at end of the Permian, with one of the most notable losses being the trilobites.
Anapsids
which would go on to evolve into turtles
Synapsids
which go on to evolve into mammals
Diapsids
which would go on to evolve into lizards, snakes, crocodilians, and dinosaurs
The Mesozoic Era – 252 to 66 million years ago
- dinosaurs evolved and became the dominant form of large terrestrial animal life.
- Many kinds of marine reptiles evolve, including the ichthyosaurs, plesiosaurs, and mosasaurs.
- The first true turtles, crocodilians, lizards, snakes, mammals, and birds evolved at this time as well.
- The first flowering plants evolved towards the end of the Mesozoic.
The Cenozoic Era – 66 to 0 million years ago
- The Cenozoic is often referred to as the Age of Mammals.
- Although mammals had been around since the Triassic, the extinction of the dinosaurs (except for birds) allowed mammals to evolve larger forms and to fill many new ecological roles.
- Grasses only become abundant at this time!
The Paleogene Period – 66 to 23 million years ago
- Global temperatures began to cool.
- Mammals diversified into a variety of new forms, including primates, bats, and whales. Birds also diversified.
The Neogene Period – 23 to 2.6 million years ago
Global temperatures continued to cool. The first hominids evolved in Africa.
The Quaternary Period – 2.6 to 0 million years ago
- The earth experienced several large glaciation events, or “ice ages”.
- The first anatomically modern humans evolved. Human civilization spread.
how long ago did non-avian Dinos exist
The non-avian dinosaurs existed for 135 million years.
The Triassic Period – 252 to 201 million years ago
- First ten million years of the Triassic, life gradually recovered from the mass extinction that occurred at the end of the Permian.
- The first mammals and dinosaurs evolved during the later portion of the Triassic, and so did the first pterosaurs
- The supercontinent Pangaea began to break apart.
- The first representatives of the ornithischians (like Pisanosaurus), theropods (like Eoraptor and Herrerasaurus), and sauropodomorphs (like Panphagia) were all mostly small and bipedal.
- amniote groups were evolving to fill them in the sea and air
what were the first vertebrates to fly ?
pterosaurs
during the triassic what were the first large herbivores
“Prosauropods” like Plateosaurus were some of the first large herbivorous dinosaurs.
what time was it that the first ichthyosaurs evolved. evolved.
Triassic
what were ancient ancestors of ichthyosaurs
terrestrial
ichthyosaurs
- To adapt to an aquatic life, ichthyosaurs evolved paddle-like front and hind limbs, a finned tail, and even a shark-like dorsal fin.
- The long snouts of most ichthyosaurs resemble those of dolphins, and are filled with conical teeth – piscivorous diet.
- ichthyosaurs never evolved gills and needed to come to the surface in order to breathe air.
when did insects evolve
as far back as the carboniferous
Pterosaurs
- commonly called, “pterodactyls”
- close relatives of dinosaurs who branched off from the reptilian family tree at roughly the same time in the Triassic that dinosaurs did.
wings of a pterosaur
pterosaurs have membranous wings supported by a single extremely elongated finger.
rhamphorhynchoids
were common in the Late Triassic and throughout the Jurassic.
what group did pterosaurs belong to
Early pterosaurs belong to a group called rhamphorhynchoids
The Jurassic Period – 201 to 145 million years ago
- Dinosaurs diversified.
- This was the peak of sauropod diversity, and they were the dominant terrestrial herbivores. Small and medium sized Ornithopods were common.
- Non-Coelurosaurian theropods, like Allosaurus, were the dominant terrestrial carnivores.
- The stegosaurs are almost completely restricted to the Jurassic, and the first ankylosaurs, Ornithopods, and ceratopsians appear at this time
- The first birds, including Archaeopteryx, evolved during the Jurassic
Pterodactyloids
Pterodactyloids differed from rhamphorhynchoids in the morphology of their tails, which were short, and the carpels in their wrists, which were elongated and made a greater contribution to the length of the wing.
where did pterodactyloids come from?
rhamphorhynchoid pterosaurs gave rise to the pterodactyloids
did rhamphorhynchoid have crests?
NO
The Early Cretaceous Period – 146 to 100 million years ago
- Dinosaurs continue to diversify
- The first flowering plants evolved. In the Early Cretaceous new theropods, like spinosaurids and carcharodontosaurids evolve, coelurosaurian theropods become more diverse, and iguanodonts become larger and more abundant.
- A third major reptilian group began patrolling the Mesozoic waters
what were the very important Early Cretaceous fossil-rich rock units.
The
- Yixian Formation of China - Wealden Supergroup of England - Cedar Mountain Formation of Utah
Mosasaurs
- Mosasaurs were relatives of modern monitor lizards and snakes.
- mosasaurs had tail fins and limbs modified into paddles, but the bodies and tails of mosasaurs were more elongate.
Varied in sized but some were true sea monsters with huge jaws and bodies. These aquatic giants seem adapted for deep-sea big-game hunting.
The Late Cretaceous Period - 100 to 65 million years ago
- Often considered the apex of non-avian dinosaur diversity, many of the most famous dinosaurs come from this period of time.
- The first flowering plants evolved.
- At the end of the Cretaceous, a large meteor collided with the earth, and this event along with its catastrophic consequences is thought to have brought about a mass extinction, which killed all non-avian dinosaurs.
what did the diversification in the late cretaceous period included
- The coelurosaurian theropods are abundant and diverse in the northern hemisphere, and include the tyrannosaurs, ornithomimids, therizinosaurs, oviraptorosaurs, dromaeosaurids, troodontids, and many more interesting clades.
- The ankylosaurs have diverged into two groups, the tail-clubbed ankylosaurids and the clubless nodosaurids.
- Ceratopsians and hadrosaurs are the dominant large herbivores in the northern hemisphere.
- Only a single lineage of sauropods remains, but the titanosaurid sauropods are the dominant herbivores in the southern hemisphere.
- Pachycephalosaurs are only known from the Late Cretaceous.
