P
H
A
N
E
R
O
Z
O
I
CE
O
N
(542
mya
to
now)
|
C
E
N
O
Z
O
I
CE
R
A
(65.5
mya
to
today) |
**************CURRENT MASS EXTINCTION CAUSED BY HUMAN
ACTIVITY ***************
University of Chicago paleontologist
David Raup estimates the background rate of extinction
on Earth throughout biological history as one species lost every four years, on average.
One recent calculation places human-caused extinction as much as 120,000 times that
level.*
* Leakey, Richard & Roger Lewin, The Sixth Extinction, New York: Doubleday,
1995. p. 241.
Neogene Period (±23.0 mya to
today)
Holocene (±11,400 years to
today): extinction of large animals in northern hemisphere; decline of woody
plants, rise of herbaceous ones; the "Age of Man"
Pleistocene (±1.8 mya
to ±11,400 years ago): four major
glaciations profoundly affect Earth's landscape and living organisms; great extinction of
species, especially the great mammals; first human social life
- ±0.125 mya, or 125,000 years ago, the
interglacial period before the one we are in right now was at its peak, the Earth's
temperature was about 2°C higher than it is now (3.6°F) and the sea level was about 5
meters higher (16.4 ft). That earlier interglacial period is called the Sangamon
in the US but the Eemian in Europe.
- ±0.5 mya, Homo sapiens, arises
- ±0.8 mya, fossils from this time found
of Homo erectus, considered the ancestral species from which modern humans,
Homo sapiens arose
- ±1.6 mya, fossils from this time found
of of Homo habilis, an early human
|
Pliocene (±5.3 to ±1.8 mya): continued rise of North
Americas western mountains, much volcanic activity; decline of forests and advance of
grasslands, with corresponding fast development of monocot plants; mastodons, saber-tooth
tigers, sloths, llamas & other "great mammals" roam the landscape
- 3+ mya, "Lucy" fossil, Australopithecus,
considered the ancestral genus from which the human genus Homo arose
- ±4.2 mya, hominid Ardipithecus
anamensis, thought to represent the root of the human evolutionary tree
|
Miocene (±23.0 to ±5.3 mya): North
America's Rocky Mountains rise for a second time, much volcanic activity in the US
Northwest, climate cooler in North America; mammals reach peak of evolution; first manlike
apes appear
- ±6 mya, hominids (humans and their
immediate direct ancestors) split from the ape branch of the primate tree of evolution
- ±15 mya, Earth's climate starts
cooling, the great forests largely are replaced with open grasslands and savannas, thus
setting the stage for human evolution (apes coming down from trees and standing upright)
- ±20 mya, first modern-type snakes
appear
|
Paleogene Period (±65.5 mya to ±23.0 mya)
Oligocene (±33.9 to
±23.0 mya): landscape in North America lower with few great mountains; climate
warmer; maximum extent of forests; in the late Oligocene songbirds (Order Passeriformes)
appear
- ±25 mya, apes arise from Prosimians
|
Eocene (±55.8 to ±33.9 mya): In
North America the mountains have eroded and there are no great inland seas; the climate is
warmer; placental mammals diversify and specialize; carnivorous mammals and hoofed ones
become established; small ancestors of the horse occur during the early Eocene
- ±36 mya, monkeys arise from Prosimians
(humans did not arise from monkeys)
- ±40 mya, first primates, called
Prosimians (looked like a cross between a squirrel and a cat)
- ±50 mya, mammalian bats arise
|
 Paleocene (±65.5 to ±55.8 mya): small mammals roam the land while sharks &
rays swim the seas
|
M
E
S
O
Z
I
CE
R
A
(251
to
65.5
mya) |
********************************FIFTH MASS
EXTINCTION************************************
(about 65 mya, probably caused by
6-mile-wide object (10 km) striking Earth at Mexico's Yucatan Peninsula, killed off
dinosaurs, about 16% of marine families and nearly half of marine genera)
 Cretaceous Period (±145.5 to ±65.5 mya): primitive mammals radiate across
Earth;during the mid-Cretaceous today's largest bird order, the Passeriformes, or
songbirds, arises; reflecting continental drift, the map at the
left show North America, Europe and Asia still stuck together, with South America, Africa
and Antarctica well separated. The large island off Africa's eastern coast is India.
- ±65 mya, dinosaurs go extinct,
apparently because of the effects of an asteroid hitting the earth; at this time already
some familiar angiosperms were present, such as sycamores, walnuts, oaks and dogwoods
- 80-90 mya, flowering plants achieve
dominance in most of the Earth's land environment
- ±100 mya, dinosaurs are the dominant
land animals while mammals occupy a small-body niche ecologically similar to that of frogs
today
- ±110 mya, first lobster, Palinurus
palaceosi; fossil found in Chiapas, Mexico
- ±120 mya, Africa and the American
continent begin splitting apart
- ±140 mya, modern-type birds arise
|
  Jurassic Period (±199.6 to ±145.5 mya): dinosaurs dominant; flying
reptiles; on land cycads, conifers and ginkgoes are dominant plants; the maps at the left
show North America, Europe and Asia squashed together above the equator, and South
America, Antarctica and most of Africa below the equator.
- ±150 mya, first flowering plants
- ±150 mya, Archaeopteryx, part
reptile, part bird
- 188-213 mya, earliest "true
frogs"
- ±195 mya, Pterosaurs, flying reptiles,
evolve from gliding reptiles
- ±200 mya, first turtles
- 200+ mya, first crocodilians, arising
from thecodonts
|
********************************FOURTH
MASS EXTINCTION************************************
(About 199-214 mya, probably caused by
massive lava eruptions from the rift causing the Atlantic Ocean to form. Volcanism
associated with this event may have caused global warming resulting in the extinction of
about 22% of marine families.)
Triassic Period (±251.0 to ±199.6 mya): first mammals and dinosaurs; land
dominated by mammal-like reptiles; oceans dominated by ammonoid cephalopods
- ±220 mya, dinosaurs evolve from
cold-blooded Thecodonts
- ±220 mya, first mammals arise from
warm-blooded Therapsids; they are shrew-like creatures living in trees and largely eating
insects
- 230-210 mya, reptilian Therapsids are
dominant land vertebrates
- ±230 mya, world's climate warms,
shifting the advantage to cold-blooded Thecodont reptiles who eat one-tenth as much food
as warm-blooded Therapsids (mammal-like reptiles)
|
|
P
A
L
E
O
Z
I
CE
R
A
(542
to
251
mya) |
********************************THIRD MASS
EXTINCTION************************************
(About 286-248 mya, the Permian Mass Extinction was the biggest
of all mass extinctions, marked by high levels of greenhouse gases, including
carbon dioxide, low levels of oxygen in the oceans and high levels of toxic gases,
possibly caused by a volcanic event igniting a continental-size layer of coal, thus
releasing carbon dioxide, or maybe it was a large meteor hitting Earth. Whatever the
cause, it killed off between 75 and 95 percent of the Earth's species, including
nearly all animals)
Permian Period (±299.0
to ±251.0 mya): continents rise, Appalachians form; decline of lycopods and
horsetails (non-flowering plants); decline of amphibians, though earliest froglike
amphibians arise toward end of Period; primitive mammal-like reptiles occur; trilobites
and many other marine forms go extinct
- 286-249 mya, amphibians begin leaving
marshes for dry uplands, many, such as Cacops, having bony plates & armor,
and some as large as ponies
|
Carboniferous Period (±359.2 to ±299.0 mya)
Pennsylvanian
(±318.1 to ±299.0 mya): land generally low, tropical, producing great
coal swamps consisting largely of forests of seed ferns and gymnosperms; first reptiles;
many primitive insects, spread of ancient amphibians; ocean reefs and banks inhabited by
algae and sponges
 Mississippian (±359.2 to ±318.1 mya): climate at first
warm and humid then cooler later as land rises; lycopods and horsetails are dominant land
plants while gymnosperms grow more widespread; amphibians go onto land, first coal-swamp
forests; in oceans echinoderms and bryozoans dominate, spread of ancient sharks
********************************SECOND
MASS EXTINCTION************************************
(About 364 mya, cause unknown, killed off
about a quarter of marine families and over half of all marine genera)
 Devonian Period (±416.0
to ±359.2 mya): first land vertebrates, amphibians ; land higher, more arid,
some glaciation; first forests, with the first gymnosperms; in seas, many corals,
brachiopods & echinoderms, as well as early fish -- lungfishes and sharks are
abundant; between 360 mya and 287 mya sharks are the dominant vertebrates in the seas
- ±360 mya, Acanthostega, part
fish part amphibian
- ±370 mya, Ichthyostega,
earliest amphibian, arise from lobe-finned fishes
- ±385 mya, Earth's first forests, formed
of a fern-like plant of the genus Wattieza
- ±390 mya, lobe-finned fishes arise,
ancestral to amphibians, now largely extinct
- ±410 mya, fish develop jaws (spiny
sharks)
- ±410 mya, Cooksonia, first
known vascular land plant, producing spores, fossil found in what is now New York, USA
|
Silurian Period (±443.7
to ±416.0 mya): land rises, with more arid regions;oldest land life-- land
plants, scorpions & insects (wingless); first jawed fishes, seas dominated by marine
arachnids
- ±425 mya, first seed plants, in form of
gymnosperms
±430 mya, first vascular plants
|
********************************FIRST
MASS EXTINCTION************************************
(About 439 mya, caused by drop of sea
levels as an ice age caused glaciers to form, and then by rising sea levels as the
glaciers melted. About a quarter of all marine families were killed off, and about 60% of
maringe genera)
Ordovician Period (±488.3
to ±443.7 mya): great submergence of land, climate over land mostly warm; first
vertebrates (jawless fishes); seas dominated by trilobites, brachiopods, bryozoans,
corals, graptolites, nautiloid cephalopods, marine algae abundant
Cambrian Period (±542.0 to ±488.3
mya): land low, land climate mild; trilobites and brachiopods dominate oceans;
first metazoans with skeletons; no known land life; most modern phyla arise in oceans |
P
R
E
C
A
M
B
R
I
A
N
(4,570
to 542
mya) |
P
R
O
T
E
R
O
Z
O
I
C(2500
to
542
mya) |
Neoproterozoic
(±1000 to ±542.0 mya)
- ±590-±505 mya, first
animals with backbones (jawless, toothless, finless fish)
- ±600 mya,
present concentration of oxygen in atmosphere achieved
|
Mesoproterozoic (±1600 to ±1000 mya)
- ±1000 mya, first green plants, in the
form of algae
- ±1500 mya, oldest fossils with
compartmentalized cells
|
Paleoproterozoic (±2500
to ±1600 mya)
- ±1900 mya, eucaryote radiation, high
atmospheric oxygen
- ±2000 mya, aerobic respiration
- ±2100 mya, multicellular eucaryotes
- ±2400 mya, aerobic photosynthesis,
rapid increase in atmospheric oxygen
- ±2500 mya, anaerobic procaryotes and
oceanic plankton diversify
|
|