Lesson 9: Stratigraphy and Geologic Time

Question 1

The tendency for rock layers to be chronologically stacked is called the ___ ___ ___.

Answer 1

Principle of Superposition.

Question 2

What is stratigraphy?

Answer 2

Stratigraphy is the science of using the arrangement and composition of rock layers to interpret geological history.

Question 3

What is a formation?

Answer 3

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.

Question 4

The Principle of Superposition allows a stratigrapher 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 radiometric dating is used. Describe radiometric dating.

Answer 4

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. 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.

Question 5

What is the geological timescale?

Answer 5

The geologic time scale is a standardized series of chronological divisions that parses the Earth’s history into discrete named units. The largest units in the time scale are Eons, followed by Eras, Periods, and Epochs.

Question 6

Describe THE HADEAN EON – 4.6 TO 4 BILLION YEARS AGO.

Answer 6

• The surface of the earth partially molten and with volcanic activity widespread.
• At roughly 4.5 billion years ago, the young earth collided with a smaller planetoid. Eventually formed the moon.
• 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.
• The oldest rocks on earth have been dated at only about 4.4 billion years old, though rocks discovered on the moon are older.

Question 7

Describe THE ARCHEAN EON – 4 TO 2.5 BILLION YEARS AGO.

Answer 7

• 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. 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, which are some of the best records of early life.

Question 8

Describe THE PROTEROZOIC EON – 2.5 BILLION TO 541 MILLION YEARS AGO.

Answer 8

• At approximately 1.7 billion years ago, the first multicellular organisms evolved. Because single-celled and early multicellular life had no bones or other hard parts and was usually microscopic, the fossil record of this early life is poor.
• Within the Proterozoic, the time span from 630 to 542 million years ago is known as the Ediacaran Period. During the Ediacaran, large forms of life with some harder parts evolved, including the first animal life.

Question 9

Describe THE PHANEROZOIC EON – 541 TO 0 MILLION YEARS AGO.

Answer 9

• 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.

Question 10

Describe The Paleozoic Era – 541 to 252 million years ago.

Answer 10

-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.

Question 11

Describe The Cambrian Period – 541 to 485 million years ago.

Answer 11

• The beginning of the Cambrian marks such a dramatic diversification of aquatic animal life that it is often referred to as The Cambrian Explosion.
• Sponges, molluscs, worms, and many kinds of arthropods (including trilobites) evolved.
• A close early relative of the vertebrates, called Pikaia, didn’t have vertebrae, but had several other features found in vertebrates.

Question 12

Refer to pg 4-5 of study guide for examples and pics of creatures from Cambrian explosion.

Answer 12

Refer to pg 4-5 of study guide for examples and pics of creatures from Cambrian explosion.

Question 13

Describe The Ordovician Period – 485 to 443 million years ago.

Answer 13

• Global sea levels were high.

- Life in the oceans continued to diversify, with fish increasingly becoming the dominant large aquatic animals.

Question 14

Describe The Silurian Period – 443 to 419 million years ago.

Answer 14

• 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.

Question 15

Describe The Devonian Period – 419 to 359 million years ago.

Answer 15

• 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.

Question 16

The Carboniferous Period – 359 to 299 million years ago.

Answer 16

• 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.

Question 17

Describe The Permian Period – 299 to 252 million years ago.

Answer 17

• The continents collided together and formed a single super continent called Pangaea.
• Reptiles evolved into three main lineages: the anapsids (which would go on to evolve into turtles), the synapsids (which go on to evolve into mammals), and the diapsids (which would go on to evolve into lizards, snakes, crocodilians, and dinosaurs).
• Many of the terrestrial rocks from this period of time represent dry, desert environments.
• 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.

Question 18

Describe The Mesozoic Era – 252 to 66 million years ago.

Answer 18

• The Mesozoic is often referred to as the Age of Dinosaurs. It is during this time that 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.

Question 19

Describe The Cenozoic Era – 66 to 0 million years ago.

Answer 19

• 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!

Question 20

Describe The Paleogene Period – 66 to 23 million years ago.

Answer 20

• Global temperatures began to cool.
• Mammals diversified into a variety of new forms, including primates, bats, and whales.
• Birds also diversified.

Question 21

Describe The Neogene Period – 23 to 2.6 million years ago.

Answer 21

• Global temperatures continued to cool.

- The first hominids evolved in Africa.

Question 22

Describe The Quaternary Period – 2.6 to 0 million years ago.

Answer 22

• The earth experienced several large glaciation events, or “ice ages”.
• The first anatomically modern humans evolved. Human civilization spread.

Question 23

The earliest primates evolved shortly after the end of the age of dinosaurs, butapes did not evolve until about ___ million years ago.From there, it’s just a short amount of time to the earliest humans whichevolved from apes about ___ million years ago.Our genius and species homosapiens have existed for about ___ years. All of recorded human history has occurred in the last ___ years.

Answer 23

12 mya.
7 mya.
200,000 yrs.
10,000 yrs.

Question 24

The non-avian dinosaurs existed for ___ million years. There is less time separating the first humans from the last dinosaurs than there is separating the last dinosaurs from the first dinosaurs.

Answer 24

135 million years.

Question 25

Describe The Triassic Period – 252 to 201 million years ago.

Answer 25

• During the 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 first vertebrates to fly.
• The supercontinent Pangaea began to break apart.

Question 26

Many of the dinosaurs from this period of time (Triassic) look fairly similar to each other. Describe some.

Answer 26

The first representatives of the ornithischians (like Pisanosaurus), theropods (like Eoraptor and Herrerasaurus), and sauropodomorphs (like Panphagia) were all mostly small and bipedal. “Prosauropods” like Plateosaurus were some of the first large herbivorous dinosaurs.

Question 27

Describe the ichthyosaurs, an amniote group that evolved to fill ecological roles in the sea during the Triassic.

Answer 27

The first ichthyosaurs evolved. The name means “fish lizard,” but ichthyosaurs are not lizards or fish. Even so, the name ‘ichthyosaur’ still seems fitting, because they are a group of reptiles that took on a fish-like lifestyle and evolved a very fishy body form. The ancestors of ichthyosaurs were fully terrestrial reptiles, but, just like the ancestors of modern whales, dolphins, seals, and sea turtles, the group found success by making an evolutionary return to the water. 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 – good equipment for a piscivorous diet. Despite their many fishlike adaptations, ichthyosaurs never evolved gills and needed to come to the surface in order to breathe air.

Question 28

Describe the plesiosaurs, another amniote group that evolved to fill ecological roles in the sea during the Triassic.

Answer 28

Most plesiosaurs had large chests and torsos, broad paddle-shaped limbs, and relatively short tails. In front of their shoulders, plesiosaurs varied tremendously. Some had short necks and huge jaws, other had elongated serpentine necks with small heads.

Question 29

Describe the Pterosaurs, an amniote group that evolved to fill ecological roles in the sky during the Triassic.

Answer 29

Pterosaurs, or as they are commonly called, “pterodactyls”, are close relatives of dinosaurs who branched off from the reptilian family tree at roughly the same time in the Triassic that dinosaurs did. Pterosaurs were the first vertebrates to fly. Unlike birds, which have arms that support wings made of feathers, and bats, which have wings made from skin stretched between multiple fingers, pterosaurs have membranous wings supported by a single extremely elongated finger. Early pterosaurs belong to a group called rhamphorhynchoids, which were common in the Late Triassic and throughout the Jurassic.

Question 30

Describe The Jurassic Period – 201 to 145 million years ago.

Answer 30

• Dinosaurs diversified.
• This was the peak of sauropod diversity, and they were the dominant terrestrial herbivores.
• Small and medium sized ornithopods were common. Noncoelurosaurian 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, although they are not particularly abundant or diverse.
• The first birds, including Archaeopteryx, evolved during the Jurassic.
• The Morrison Formation of the western USA, and the Solnhofen limestone of Germany, are some of the best and most famous records of dinosaurs from this time.

Question 31

In the Jurassic, rhamphorhynchoid pterosaurs gave rise to a new pterosaur group: the pterodactyloids. Describe them.

Answer 31

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. Unlike rhamphorhynchoids, many pterodactyloids had large head crests, which were presumably display structures. There were many species of small pterodactyloids, some smaller than a robin, but some species had wingspans of over ten meters, making them the largest animals to ever fly.

Question 32

Extra, sauropods: slender-necked Diplodocus is ___ and Brachiosaurus is ___. Heaviest?

Answer 32

Long.

Tall.

Question 33

Describe The Early Cretaceous Period – 146 to 100 million years ago.

Answer 33

• Dinosaurs continue to diversify and the first flowering plants evolved.
• In the Early Cretaceous new theropods, like spinosaurids and carcharodontosaurids evolve, coelurosaurian theropods (feathery integument?) become more diverse, and iguanodonts become larger and more abundant.
• The Yixian Formation of China, the Wealden Supergroup of England, and the Cedar Mountain Formation of Utah are important Early Cretaceous fossil-rich rock units.

Question 34

Sometime in the Cretaceous Period, a third major reptilian group began patrolling the Mesozoic waters. Describe them.

Answer 34

Mosasaurs were relatives of modern monitor lizards and snakes. Like ichthyosaurs and plesiosaurs, mosasaurs had tail fins and limbs modified into paddles, but the bodies and tails of mosasaurs were more elongate. Many mosasaurs are the right size to have preyed on small and medium sized fish, but some were true sea monsters with huge jaws and bodies over eighteen meters long. These aquatic giants seem adapted for deep-sea big-game hunting, and they likely ate large fish and other marine reptiles.

Question 35

Describe The Late Cretaceous Period - 100 to 65 million years ago.

Answer 35

• Often considered the apex of non-avian dinosaur diversity, many of the most famous dinosaurs come from this period of time.
• 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.
• The first flowering plants evolved.
• At the end of the Cretaceous, a large meteor collided with the earth and is thought to have brought about a mass extinction, which killed all non-avian dinosaurs.

Question 36

___ time separates us from Tyrannosaurus than separated Tyrannosaurus from Stegosaurus.

Answer 36

Less.