Transcript Chapter 3

Geologic Time
Methods of Dating Rocks
1. Relative dating - Using fundamental principles
of geology (Steno's Laws, Fossil Succession,
etc.) to determine the relative ages of rocks
(which rocks are older and which are younger).
2. Absolute dating - Quantifying the date of the
rock in years. This is done primarily by
radiometric dating (or analysis of the
breakdown of radioactive elements in the rocks
over time).
Geologic Time Scale
• The geologic time scale has been
determined bit-by-bit over the years
through relative dating, correlation,
examination of fossils, and radiometric
dating.
• Boundaries on the time scale are drawn
where important changes occur in the
fossil record, such as extinction events.
Geochronologic Units
The geologic time scale is divided into a number
of types of units of differing size. From the
largest units to the smaller units, they are:
• Eons
• Eras
• Periods
• Epochs
These units are geochronologic units.
Geochronologic units are time units.
Eons
Eons are the largest division of geologic
time.
• Precambrian - oldest rocks on Earth
• (2.5 billion to 542 million years ago) Beginning of
life.
• Phanerozoic Eon - "visible life" (542 million
years ago to present)
The Precambrian
The Hadean, Archean and Proterozoic eons
are together referred to as the
Precambrian, meaning “before the
Cambrian Period”.
The Precambrian covers 87% of geologic
history.
Precambrian
divisions
Hadean Eon, informal division of Precambrian time occurring between about
4600 million (4.6 billion) and about 3800 million years ago. The Hadean Eon is
characterized by Earth’s initial formation—from the accretion of dust and gases
and the frequent collisions of larger planetesimals. Throughout part of the eon,
impacts from extraterrestrial bodies released enormous amounts of heat that
likely prevented much of the rock from solidifying at the surface. As such, the
name of the interval is a reference to Hades, a Greek translation of the Hebrew
word for hell.
www.brittanica.com Written by John P. Rafferty
Last Updated 4-12-2012
During this time the moon was formed by a collision between Earth and a
planetoid. The first atmosphere escapes, and the second atmosphere is
formed.
Precambrian
divisions
The Archean Eon began about 3800 million years ago with the formation of the
Earth’s crust and extended to about 2500 million years ago. Surface of the Earth
cools from molten to solid rock. Water starts to condense and atmosphere consists
of nitrogen and carbon dioxide. First evidence of the earliest primitive life-forms—
bacteria and blue-green algae—appears in rocks about 3.5 billion (3500 million)
years old. Archean greenstone-granite belts contain many economic mineral
deposits, including gold and silver. Oldest record of Earth’s magnetic field.
www.Britannica.com
Written by Brian Frederick Windley
Precambrian
divisions
Proterozoic Eon - starting about 2500 million years ago to about 544 million
years ago. First stable continents appear, first free oxygen in atmosphere.
Creation of banded iron formations. As anaerobic organisms are poisoned by
oxygen, single celled photosynthetic organisms proliferate. Formation of the
ozone layer blocks radiation from the sun. First Eukaryotic cells appear.
Supercontinents form and break up. Soft bodied organisms and shelled
invertebrates appear.
650 million years ago, mass extinction of 70% of dominant sea plants is caused
by global glaciation.
Eras
There are three eras in the Phanerozoic
Eon. Eras are divided into geologic
periods. In order from oldest to youngest,
the three eras are:
• Paleozoic Era - "ancient life" (such as
trilobites)
• Mesozoic Era - "middle life" (such as
dinosaurs)
• Cenozoic Era - "recent life" (such as
mammals)
Periods
Eras are divided into periods.
Paleozoic Era
•
•
•
•
•
•
•
Permian Period
Pennsylvanian Period
Mississippian Period
Devonian Period
Silurian Period
Ordovician Period
Cambrian Period (oldest)
Cambrian Period (542 to 488.3 mya)
- Abundance of multicellular life.
- Most of the major groups of animals
first appear
- 510 mya: Vertebrates appeared in
the ocean.
- first trilobites
The Ordovician Period (490 to 443 mya.
- Best known for diverse marine invertebrates, including trilobites,
brachiopods, primitive fish, cephalopods, corals, criniods, gastropods.
gastropod
crinoid
brachiopod
cephalopod
Silurian Period
- Melting of large glacial formations
contributed to a rise in sea levels
- Coral reefs appear
- First freshwater fish
- First fish with jaws
- First evidence of life on land
- Proliferation of Ordovician species
Devonian Period
- First vascular plants
- First seed plants
- First tetrapods (reptile)
- First terrestrial arthropods
- Sea life abundant
- Soils before this time were
predominantly red, after soils
were dark due to organic
accumulation.
- Glaciation and lowering of
the sea level triggered a
mass extinction at the
end of the Devonian.
Devonian Period Life
The Mississippian and Pennsylvanian
Periods are known as the
Carboniferous Periods
- Rich deposits of coal found in beds
from this time due to vast amounts
of tropical plant material
- First amniotic eggs allow tetrapods
to lay eggs without fear of
desiccation
- Trilobites become scarce, heavily
armored Devonian fish become
extinct, more modern looking fish
appear.
Mississippian Period – environment was heavily marine, with seas covering
part of the continent.
Pennsylvanian Period – environment is alternating marine and terrestrial, with
transgression and progression of seas caused by glaciation.
Mississippian/Pennsylvanian Period
Permian Period (the Great Dying)
- Biggest mass extinction recorded in
the history of life on Earth (loss of most
of the marine invertebrates of the time)
- Great forests of ferns died off leaving
room for plants with enclosed seeds
- Loss of earlier species makes way for
the age of dinosaurs
• Late Permian land masses
Mesozoic Era
• Cretaceous Period
• Jurassic Period
• Triassic Period (oldest)
Mesozoic Era
Meso (middle) zoic ( life or animals) is the
time between the Paleozoic (ancient life)
and the Cenozoic (New life)
Began with the Permian extinction, the
largest extinction event in the history of the
Earth.
Ends with the Cretaceous-Paleogene
extinction event, which killed off non-avian
dinosaurs.
Triassic Period
(248 to 213 mya)
Named for three distinct rock layers from
this time period found throughout Germany
and NW Europe. These are red beds,
capped by chalk, followed by black shale.
Triassic Period
The supercontinent Pangea existed at the beginning
of the Triassic, but began to split apart in two
separate landmasses, Laurasia and Gondwana.
– Environment was hot, vast deserts and warm seas.
Even the polar regions had forests.
– First mammals and dinosaurs appear
– After the continent breakup –
more extinctions.
http://stevengoddard.files.wordpress.com/2
011/07/g-44.gif%3Fw%3D640
Herrerasaurus – one
of the first true
dinosaurs, 10 ft long
and 100 to 400 lbs.
Eoraptor – only about 20 lbs.
Also one of the first known
dinosaurs
http://www.walkingwithdinosaurs.com/din
osaurs/detail/herrerasauru
paleontologist
http://faculty.etsu.edu/gardnerr/planetarium/dino/triassic.htm
Jurassic Period
(213 to 145 mya)
Primitive mammals are
still around, the descendants
of which are with us today:
duck bill platypus, marsupials like kangaroos and
opossum. Birds make an appearance.
But dinosaurs ruled the Jurassic. The tallest and
largest creatures that ever existed on Earth
came into being, while some reptiles moved back
into the sea.
(dinosaur = thunder lizard)
http://www.hudsonfla.com/1hst.htm
Jurassic Period
(213 to 145 mya)
Archaeopteryx, known as the first bird
Megazostrodon – first mammal
during the Jurassic period.
Mammals could not dominate
during the reign of the dinosaurs,
as the dinosaurs were huge.
http://dinosaurs.about.com/od/dinosaurbasi
cs/tp/12bestdinos.htm
Stegosaurus – known for its tiny brain
Jurassic Period
(213 to 145 mya)
Allosaurus was smaller,
faster and more vicious
than the better known
(and later) T-Rex, and
may have hunted in
packs
http://dinosaurs.about.com/
od/dinosaurbasics/tp/12best
dinos.htm
Giant sauropods were very successful
during the Jurassic
jurassic dinosaurs
Cretaceous Period
(145 to 65 mya)
• Named for the Latin word for chalk.
However in many parts of the world formations from this
period are limestone from the shallow seas.
• Longest period of the Phanerozoic.
• Warm climate, lots of inland seas
• Lots of marine animals and birds, but dinosaurs
dominate on land
• First flowering plants appear
Cretaceous Period
• The end of the Cretaceous is marked by an iridium rich
layer found worldwide thought to be associated with the
impact crater that created the Gulf of Mexico.
• There is also evidence of a series of huge volcanic
eruptions along the tectonic border between India and
Africa that began just before the impact. It is likely that
these regional catastrophes combined to precipitate
climatic change.
• These climate changes are most likely what brought
about the demise of all dinosaurs with the exception of
birds
•
http://www.livescience.com/29231-cretaceous-period.html#sthash.3pzQoyXQ.dpuf
The diversity of life in the
Cretaceous was
unparalleled, including a
large number of large
marine animals, as well as
flying dinosaurs
Tyrannosaurus rex is part of the
carnivorous groups of dinosaurs
that, according to new research,
maintained a stable level of
biodiversity leading up to the mass
extinction at the end of the
Cretaceous. http://www.livescience.com/29231-cretaceousperiod.html#sthash.3pzQoyXQ.dpuf
Titanosaurs, such as this
Alamosaurus were
herbivores that thrived
during the late
Cretaceous.
Cenozoic Era
Eras are divided up into Periods
• Quaternary Period (youngest – today)
• Tertiary Period (oldest)
Epochs
Periods can be subdivided into epochs
Epochs of the Cenozoic Era
– Holocene Epoch (youngest - today)
– Pleistocene Epoch
– Pliocene Epoch
– Miocene Epoch
– Oligocene Epoch
– Eocene Epoch
– Paleocene Epoch (oldest)
Paleocene (65 – 55.5 mya)
• Paleocene means “old recent”
• Starts with mass extinction event - the
remaining dinosaurs die out
• Early Paleocene Earth was dark and cold
due to clouds of dust
• Late Paleocene was almost as warm and
humid as the Cretaceous.
• Mammals were still small
• Birds were plentiful, some were
huge predatory meat eaters
• Example: Gastornis – stands 6.5 ft,
eats meat, does not fly.
Crocodiles survived, also snakes.
Example: Titanoboa – 50 ft long
and weighing more than one ton.
Eocene Epoch (55.5 – 33.7 mya)
• Similarities in plants and animals in North America and
Europe indicate these regions were still in contact or
very close
Eocene
First appearance of
artiodactyls – even toed
herbivore/omnivore that
would become pigs, cows,
sheep, goats, giraffes,
hippos and camels and
Whales!
• First appearance of
perissodactyls – odd
toed herbivores that
would become horses,
zebras, donkeys, tapirs,
rhinos
Oligocene (33.7 – 23.8 mya)
Continents are near
their present day
locations.
Decrease in average
global temperatures
• Spread of newly evolved grasses opened a new niche
for grazing animals. Early horses and proto-camels
abound in North America
• In South America, several very large animals evolve
Pyrotherium – elephant like
hooved animal about 10 ft
long and 5 ft tall
http://prehistoric.ucoz.ru/img/tm/Pyrotherium.jpg
Indricotherium,, a close
rhinoceros relative, was the
largest land mammal to ever live,
at about 5.5 meters (18 feet) tall
at the shoulder, 9 meters (30
feet) long, weighing around 20
tons.
Miocene (23.8 – 5.3 mya)
20 million years ago, Antarctica was covered by ice and the
northern continents were cooling rapidly. The world has taken
on a "modern" look, but notice that Florida and parts of Asia
were flooded by the sea.
http://www.scotese.com/miocene.htm
• Dense forests give way to open deserts,
tundra and grasslands.
• Herbivores become faster, large predatory
animals and birds dominate.
• Increased seasonality.
Chalicothere, a Miocene mammal from
Kazakhstan. Chalicothere was an oddtoed hoofed mammal, or Perissodactyl
Desmostylus hesperus, an amphibious
mammal from the Miocene that lived in
North America and Eastern Asia. (Source:
Wikimedia Commons, artist Nobu Tamura.
Pliocene (5.3 – 1.8 mya)
• During large chunks of the Pliocene epoch, Eurasia,
North America and South America were all connected by
narrow land bridges--and it wasn't all that difficult for
animals to migrate between Africa and Eurasia, either.
This resulted in increased competition, displacement and
even outright extinction. For example, camels (like the
huge Titanotylopus) migrated from North America to
Asia. Apes and hominids were mostly restricted to Africa,
though there were scattered communities in Eurasia and
North America as well. The first land bridge connecting
North and South America led to the demise of many
South American species of animals.
1.dinosaurs.about.com/od/CenozoicEra/a/Pliocene-Epoch.htm
Some familiar mammals
appeared, such as the
Woolly Mammoth, Saber
Toothed Tigers, and the Giant
Sloth (7 meters tall) and Giant
Armadillo (weighed 1 ton)
Pleistocene
(1.8 mya to about 11,700 years ago)
• Most recent episodes of ice ages occur, glaciers
advance and retreat. Most of North America covered by
ice at least 11 times.
• By the end of the Pleistocene/Early Holocene many
large mammals like Mammoth, Mastadon, Saber Tooth
Tigers and Giant Sloth became extinct
• The La Brea Tar Pits in Los Angeles California is one of
the most famous Pleistocene fossil locations in the
world.
Homo neanderthalensis appeared
about 200,00 years ago and became
extinct about 28,000 years ago
Neandertal
modern Homo sapiens
Homo sapiens also appeared during the
Pleistocene, about 200,00 years ago. By the
end of the period they had spread from
Africa and were found worldwide
Holocene
(11,700 years ago to the present)
Continental motions due to plate tectonics are less than a
kilometer over the last 10,000 years. However, ice melt
caused world sea levels to rise about 35 m (115 ft) in the
early part of the Holocene.
• Impact of humans and technology
• climate warming following the last ice age
• • continents drying out, polar areas contract
• • plant communities shifting with the climate
http://www.ucmp.berkeley.edu/quaternary/holocene.php
Chronostratigraphic units
Chronostratigraphic units are the actual
rocks formed or deposited during a
specific time interval.
(They are sometimes called time-rock units.)
Periods and Systems
Geochronologic units (time units) have the
same names as the chronostratigraphic
units (time rock units) that they represent.
For example, the Cambrian System is a
rock unit, and the Cambrian Period is a
time unit.
The rocks of the Cambrian System were
deposited during the Cambrian Period.