How old is this planet anyway?

– The Universe is probably ~13 billion years

old (Big Bang Theory/Doppler Shift)
– Earth is ~4.5 billion years old (begins with
cooling of crust/solidification)
– Earliest records of life ~3.5 billion years ago
– First humans (Australopithecus), 0.005
billion years ago
– Discovery of Australopithecus fossils ,
0.0000000002 billion years ago
Physical conditions of early Earth

• Temperatures in correct range (in

general, water in fluid state, carbon
compounds non-brittle)
• Size of planet retains an atmosphere
• Early atmosphere lacked oxygen,
therefore highly reductive
• High energy bombardment from sun
promotes generation of organics
• The Age of Earth

During the 1800s,

geologists, paleontologists, and
naturalists found several forms of
physical evidence that confirmed that
Earth is very old.
• The Age of Earth
• The evidence includes:

Fossils of ancient sea life on dry land far from oceans. This supported the idea that the
Earth changed over time and that some dry land today was once covered by oceans.

The many layers of rock. When people realized that rock layers represent the order in
which rocks and fossils appeared, they were able to trace the history of Earth and life
on Earth.

Indications that volcanic eruptions, earthquakes, and erosion that happened long ago
shaped much of the Earth’s surface. This supported the idea of an older Earth.
• Geologic Time Scale

• Geologists and other Earth scientists use geologic time scales to describe when events
happened in the history of Earth. The time scales can be used to show when both
geologic events and events affecting plant and animal life occurred. The geologic time
scale illustrates the timing of events like:


Earthquakes.

Volcanic eruptions.

Major erosion.

Meteorites hitting Earth.

The first signs of life forms.

Mass extinctions.
 About 3.5 - 3.8 billion years of simple cells (prokaryotes).
 3 billion years of photosynthesis.
 2 billion years of complex cells (eukaryotes).
 1 billion years of multicellular life.
 600 million years of simple animals.
 570 million years of arthropods (ancestors of insects, arachnids and crustaceans).
 550 million years of complex animals.
 500 million years of fish and proto-amphibians.
 475 million years of land plants.
 400 million years of insects and seeds.
 360 million years of amphibians.
 300 million years of reptiles.
 200 million years of mammals.
 150 million years of birds.
 130 million years of flowers.
 65 million years since the non-avian dinosaurs died out.
 2.5 million years since the appearance of Homo.
 200,000 years since the appearance of modern humans.
• Periods
• Birth of Earth - approximately 4600 million years ago - The Hadean Period (4600
m.y. - 3800 m.y.)
• Scientists estimate that our planet, Earth, formed around 4600 million years ago.
The oldest rocks dated so far are from the Acasta Gneiss Complex near Great Slave
Lake, Canada with an age of about 4030 million years.
• The first algae - 1200 million years ago - The Proterozoic Era (2500 m.y. - 544 m.y.)
• The final Era of the Precambrian, the Proterozoic Era, spans the time between 2500
million and 544 million years ago. Fossils of both primitive single celled and more
advanced multicellular organisms begin to appear in abundance in rocks from this
era. The name, proterozoic, means "early life."
• The Vendian animals - 570 million years ago - The Vendian Period (650 m.y. -
544 m.y)
• The first animals in the fossil record appeared between 620 and 550 million years
ago. This period is called the Vendian after the stratigraphic sequence in Russia
where rocks of this age are especially well developed.
• The Cambrian Explosion - The Cambrian Period (544m.y.- 505 m.y.)
• The earliest period of the Palaeozoic era is called the Cambrian Period. It is
named after Cambria, the Roman name for Wales, where rocks of this age were
first identified by the nineteenth century geologist Adam Sedgwick. Cambrian
sediments, however, are by no means restricted to Wales but found in many
other parts of the world.
• The Rise of the fish - The Ordovician Period (505 m.y.-440 m.y.)
• The time between 505 and 440 million years ago is called the Ordovician. It is
named after a Celtic tribe called the Ordovices. At this time, the area north of the
tropics was almost entirely ocean, and most of the world's land was collected
into the southern super-continent Gondwana. Throughout the
Ordovician, Gondwana shifted towards the South Pole and much of it was
submerged underwater.
• Venturing on land - the Silurian Period (440 m.y. - 410 m.y.)
• The Silurian period, named after a Celtic tribe called the Silures, was the time
when some plants and animals left the water and colonized the land for the first
time. 
• Invasion of the land - the Devonian Period (410m.y. - 360m.y.)
• The Devonian period was named after Devonshire, England, where rocks of this
age were first studied. During the Devonian, early arthropods and vertebrates
continued to colonise the land. The animals had to solve the same problems that
plants faced when they moved to the land, such as reducing water loss and
maximising oxygen uptake. The evolutionary advances that solved these problems
not only allowed animals to invade land, but also to radiate over the continents.
• Reptiles and Conifers - the Carboniferous Period (360m.y. - 286m.y.)
• The Carboniferous Period extended from 360 to 286 million years ago. The term
"Carboniferous" comes from England, in reference to the rich deposits of coal
(carbon) that occur there.
• Pangea - the Permian Period (286m.y.- 248m.y.)
• By Permian times, the continents were moving even closer together than during the
Carboniferous as the northern and southern supercontinents
of Laurasia and Gondwana began to assemble into a single great landmass,
called Pangaea. The Permian period was the final period of the Paleozoic era and is
named after the province of Perm, Russia, where rocks of this age were first studied.
• Mammals and dinosaurs - the Triassic Period (248m.y.-213m.y.)
• The Triassic period was the earliest period of the three Mesozoic eras (Triassic -
Jurassic - Cretaceous).The name Triassic refers to the threefold division of rocks of this
age in Germany. Mesozoic means "middle animals", and is the time during which the
world fauna changed drastically from that which had been seen in the Paleozoic. 
• Dinosaurs and birds - the Jurassic Period (213 m.y. - 145 m.y.)
• The Jurassic period was the middle period of the Mesozoic era, spanning the time
between 213 and 145 million years ago. It is named after the Jura Mountains between
France and Switzerland, where rocks of this age were first studied. The Jurassic has
become a household word with movies like Jurassic Park.
• The final season of the dinosaurs - The Cretaceaous Period (145m.y.-65m.y.)
• This period lasted longer than the whole of the succeeding and as yet unfinished era, the
Cenozoic. It was a time when many of the typically Mesozoic lifeforms - ammonites,
belemnites, gymnosperms, ichtyosaurs, plesiosaurs, pterosaurs and dinosaurs - were in
decline. But all of these groups radiated and diversified during some or all of their time
and towards the end of the late Cretaceous they showed a variety of patterns of
extinction.
• Archaic mammals and early primates - the Palaeocene Epoch (65m.y.- 55.5m.y.)
• The Palaeocene was the earliest epoch of the Tertiary period, spanning the time
between 65 and 55.5 million years ago. It is named after the Greek words "palaois" (old)
and "ceno" (new), indicating the presence of new fauna and flora associated with the
old ones from the Cretaceous. The world at that time was a much more equable place
than it is today, with a tropical or subtropical type of climate reaching to the Polar
Regions.
• Whales and horses - The Eocene Epoch (55.5 m.y. - 33.7m.y.)
• The epoch after the Palaeocene is called the Eocene. Its name derives from the Greek
words "eos" (dawn) and "ceno" (new), i.e., the dawning of new fossil forms. Towards
the end of the Palaeocene and until about 50 million years ago in the early Eocene, the
global climate grew notably warmer. 
• Grasses and primates - the Oligocene Epoch (33.7m.y. - 23.8m.y.)
• The Oligocene epoch of the early Tertiary period, spanned the time
between 33.7 and 23.8 million years ago and is named after the Greek
words "oligos" (little, few) and "ceno" (new) indicating that there were
only a few new fossil types. 
• Kelp forests and horses - the Miocene Epoch (23.8 m.y. - 5.3m.y.)
• The Miocene was named from the Greek words "meion" (less) and "ceno"
(new). During this period there were less new fossil forms than during the
following epoch, the Pliocene. It was a time of generally warmer global
climates than those in the preceding Oligocene, or the following Pliocene.
• The first hominids - the Pliocene Epoch (5.3 m.y. - 1.8 m.y.)
• The final epoch of the Tertiary period is called the Pliocene epoch and is named after the Greek words
"pleion" (more) and "ceno" (new) meaning that there were more new fossil forms than previous epochs.
The gradual cooling that began in the Eocene continued through the Miocene and into the Pliocene; it
represents the final stages of a global cooling trend that led up to the Quaternary glaciations. 
• Glaciation, the Moa and Homo sapiens - the Pleistocene Epoch (1.8 m.y. - 10,000 y.)
• The Pleistocene was the penultimate epoch of the Quaternary period, spanning the time between 1.8
million years ago up to the beginning of the Holocene at 10,000 years ago. It is named after the Greek
words "pleistos" meaning "most" and "ceno" meaning "new" fossil forms.
• The Age of Humans - the Holocene Epoch (8,000 years - present)
• The final epoch of the Quaternary period, spanning the time from the end of the Pleistocene (10,000
years ago) to the present is the Holocene epoch, named after the Greek words "holos" (entire) and
"ceno" (new), indicating it contains entirely new fossil assemblages.
 Archean Proterozoic Eon
Hadean
(Early Earth (Period of (Period of
Appearance of appearance of the
Development)
first prokaryotes) first eukaryote)

Paleozoic era
Mesozoic era
Cenozoic era (Dominance of
(Dominance of
(Recent Life) appearance of
dinosaurs)
trilobites)
 The Evolution of Man
“Mankind stood up first and got
smart later”
Stephen Jay Gould
Placental mammals included the Hominoids...
• Apes include Gibbons (Hylobates),
Orangutan (Pongo), Gorillas (Gorilla)
and Chipanzees (Pan)
– Most are ground dwelling and lack tails
– Some are closely related to Homo sapiens
in terms of nuclear DNA:
• Gorilla (97.7%) diverged 8 mya
• Pan (98.4%) diverged 6 mya
• Hominids include Ardipithecus,
Australopithecus, and Homo
 Hominids
• Earliest hominids diverged ~5 mya (Ardipithecus)
• Distinguished by bipedal stance
• Most fossil specimens of early hominids are
Australopithecus
• Appearance in fossil record coincident with
cooling of Africa to convert rain forests to
savannah plain, resulting in a rapid adaptive
radiation of at least 6 species
 Australopithecus - forerunner or
evolutionary dead end?
• Apelike - large face, small skull/brain size
(400 cm3). Bipedal, developed grip
• Well developed teeth, indicating movement to
tougher foods that required more physical
digestion
• Systematics provide little information on
relationships between various species of
Australopithecus
– e.g. “Lucy”, 1974: A. afarensis
 The first humans, early Homo
• Genus Homo distinguished by larger brain
size ≤ 700 cm3, evolving 2 mya
• First association with tools: Homo habilis,
“handy man”. Short, long arms - intiially
thought to be a species of Australopithecus
• Mystery species H. rudolfensis had larger
brain, appeared to co-exist with H. habilis
 Late Homo

• Homo erectus, the first true human?

• Very large brain: 1000cm3
• Probably not the direct ancestor of modern man
• May have had speech ability
• Cave-dwelling hunters, used fire, clothed in
animal skins
• Nomadic, responsible for rapid spreading into
Asia and Europe by 0.5 mya
 The final phase...

• Homo neanderthalensis orginated in Africa,

but rapidly spread to other continents. Very
common 100,000 years ago, but not the
ancestor of modern man. Disappeared
35,000 ya
• Examination of burial grounds suggests social
ritualism - the first evidence of abstract
thought
 Homo sapiens

• probably evolved from H. heidelbergensis, a

close relative of H. neaderthalensis
• Oldest known H. sapiens fossil is 130,000 years
old, cranial capacity of 1500 cm3
• Controversy over origin
– Monogenesis model*
– Multiregional model
 And now...

• Currently in the Recent epoch of the

Quarternary period of the Cenozoic era
• History may tell of a third mass extinction?
• Radically changing planet will continue to
apply selective pressure to species