Just the Facts Prehistoric World.pdf

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I NFORMATION A T Y OUR
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PREHISTORIC
WORLD
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CONTENTS
• Oldest minerals, rocks and meteorites • The Precambrian eon
• Phanerozoic eon to present day • Major events • Previous estimates
of the age of the Earth • Geological timescale
• Continental drift • Seafloor spreading • Another theory
• Some speeds • Features of the Earth caused by plate movement
• Cross section of the Earth
• Types of rock • Sediments to sedimentary rock • Examples of igneous
rock • Examples of sedimentary rock • The rock cycle • Examples of
Metamorphic rock
• How fossils form • The uses of fossils • Before fossilization
• During fossilization • Fossil assemblages • After fossilization
• Precambrian world • Stromatolites • Vendian period
• Snowball Earth • Animals of the Vendian
• Paleozoic era • Land animals • Cambrian • Ordovician • Silurian
• The Burgess Shale • Calymene • Diplograptus
• The world in the Devonian period • Plants • The age of fish
• Changing atmosphere • Old red sandstone • Cephalaspis
• Eusthenopteron • Ichthyostega
• The world in the Carboniferous period • One period or two?
• Formation of coal • Coal forest plants • Eogyrinus • Meganeura
• Westlothiana
• The world in the Permian period • Desert features • Reefs
• Mesosaurus • Pareiasaurus • Dimetrodon
• The world in the Triassic period• Mesozoic era • Glossopteris
• Meaning of the name • New plant life
• Reasons for the mass extinction • Triassic climates
• Changing plants, changing animals • Hard-shelled egg: the key
to land-living • Footprints • What makes a dinosaur? • Eoraptor
• Thecodontosaurus • Eudimorphodon
• The world in the Jurassic period • Mass extinctions • Meaning of the
name• Typical Jurassic rocks • Two Jurassic rock sequences • Economic
importance • Index fossils
• The life on a continental shelf • Cryptoclidus
• The fossils of the lagoons • Liopleurodon
• Pterodactylus
• Dinosaur types • A dinosaur landscape • Stegosaurus
• Diplodocus
• The world in the Cretaceous period • Diverse dinosaurs
• Meaning of the name • Tylosaurus • Animals of air and sea
• Elasmosaurus • Kronosaurus • Arambourgiana
• Saltasaurus • Caudipteryx
• Velociraptor • Tyrannosaurus • Therizinosaurus
• Carnotaurus
• New plants • Varied habitats
• Iguanodon • Parasaurolophus • Euoplocephalus • Triceratops
• What caused the Great Extinction? • Diseases
• Meteorite or comet strike • Changing climates • Volcanic activity
• A combination of all of these • Winners and losers • Repenomamus
• The world in the early Tertiary period • Plant and animal life
• Meaning of the name • Mammal names • Brontotherium •
Hyracotherium • Diatryma • Oxyaena
• The world in the late Tertiary period • Phorusrhacos • The coming of
grass • Deinotherium • Synthetoceras • Sivatherium
• Cooling climate
• The world in the Quaternary period • Causes of the Ice Age • Meaning
of the name • Ages of the Quaternay • Glacial stages • Evidence of
glaciation • Smilodon • Elephas Primigenius • Megatherium • Macrauchenia
This edition published in the United States in 2006 by School Specialty Publishing, a member of the School Specialty Family.
Copyright © ticktock Entertainment Ltd 2005 First published in Great Britain in 2005 by ticktock Media Ltd. Printed in China.
• When and where did human beings first appear? • Why did we stand
upright? • Orrorin • Ardipithecus • Kenyanthropus
• Australopithecus
• Out of the cradle • The development of culture and civilization
• Homo
• Timeline of the History of Geology and Palaeontology • Some wrong
deductions
• Dinosaurs all around the world • Finding dinos • Excavation and
transportation • In the lab • Dino displays • Museums with dinosaur
collections
All rights reserved. No part of this book may be reproduced, stored in a central retrieval system, or transmitted in any form or by
any means, electronic, mechanical, photocopying, recording, or otherwise, withouth the prior written permission of the publisher.
Written by Dougal Dixon. Special thanks to Elizabeth Wiggans.
Library of Congress-in-Publication Data is on file with the publisher.
Send all inquiries to:
School Specialty Publishing
8720 Orion Place
Columbus, OH 43240-2111
ISBN 0-7696-4258-6
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HOW TO USE THIS BOOK
UNCOVERING THE
PREHISTORIC WORLD
KEY FIGURES
WILLIAM BUCKLAND
EDWARD DRINKER
COPE
MARY ANNING
LOUIS SEYMOUR BAZETT LEAKEY
1902 Walter Sutton discovers the
chromosome theory of inheritance.
1902 Physicist Ernest Rutherford
shows that radioactivity means that
the Earth is older than Kelvin said.
1912 Alfred Wegener proposes
continental drift.
1927 Belgian priest Georges
Lemaître proposes that the universe
began with the explosion of a
primeval atom—a forerunner of the
Big Bang theory.
1934 American geologist Charles F.
Richter establishes the Richter scale for
measuring earthquakes.
1946 Geologist Reg Sprigg finds the
oldest fossils of multicellular organisms
in Australia.
1956 Keith Runcorn notes polar
wandering based on paleomagnetic
studies.
SOME WRONG
DEDUCTIONS
1650 Irish Archbishop
Ussher calculates date of
Creation at 4004 BC.
This is widely accepted.
Dates: 1903–72
Nationality: British/Kenyan
Best known for: Louis Seymour
Bazett Leakey was born in Kenya.
He became an archaeologist and
proved Darwin’s theory that humans
evolved in Africa. His most
significant work was done in Olduvai
Gorge in Tanzania where he found
evidence of early tool use.
Key discoveries: Various species of
Australopithecus, but given different
names at the time.
SIR RICHARD OWEN
Dates: 1804–92
Nationality:
British
Best known
for: Sir Richard
Owen became
the most
important anatomist
of his day, determining that the
way an animal lived could be
deduced by its shape and the
organs it possessed. However, he
could not quite grasp the newly
developed concept of evolution.
Key discoveries: Coined the
term dinosauria in 1842, to
encompass three new animal
fossils recently discovered,
from which we get the name
dinosaur.
Dates: 1784–1856
Nationality: British
Best known for: William Buckland
was a geology lecturer at the
University of Oxford. He toured
Europe and established the basic
principles of stratigraphic correlation
and became a scientific celebrity on
his discovery of Megalosaurus. He
was the Dean of Westminster from
1845 to his death in 1857.
Key discoveries: Megalosaurus,
the first dinosaur to be scientifically
described.
T he history of life on Earth is pieced together through the detailed accumulation of
knowledge gained over the centuries by visionary and hard-working scientists.
A list such as this cannot be exhaustive. There are many others whose contributions were as
great but just did not make it on to this page because of lack of room.
Darwin studied the features
of different species to develop
his theory of evolution.
J UST THE FACTS, PREHISTORIC WORLD is a quick and easy-to-use way to look up facts
Alfred Wegener
1824 Buckland describes the first
dinosaur.
1830 Charles Lyell publishes his
influential Principles of Geology.
1837 Charles Darwin uses natural
selection to explain evolution, but the
idea is not published until 1859.
1837 Swiss scientist Louis Agassiz
detects the Ice Age.
1841 William Smith’s nephew, John
Phillips, names the geological eras
Palaeozoic, Mesozoic, and Cenozoic.
1842 Sir Richard Owen invents the
term dinosaur.
1848 Science magazine established
by the American Association for the
Advancement of Science.
1866 Austrian monk Gregor Mendel
establishes the laws of heredity. His
work remains unknown until about
1900.
1871 Darwin publishes The Descent
of Man.
1894 Eugene Debois describes
Pithecanthus erectus (now Homo
erectus) as the missing link between
humans and apes.
1961 Amateur meteorologist GS
Callander notes the rise in greenhouse
gases in the atmosphere and warns of a
global warming.
1963 Fred Vine and Drummond
Matthews discover seafloor spreading.
This leads to the establishment of plate
tectonics.
1964 Arno Penzias and Robert
Wilson detect cosmic radiation and
use it to confirm the Big Bang Theory.
1966 Willi Hennig develops
cladistics, a new approach to studying
evolutionary relationships.
1969 Moon rock samples prove that
the moon the same age as the Earth.
1972 Stephen Jay Gould and Niles
Eldredge develop the theory of
punctuated equilibrium, meaning that
evolution takes place in short bursts.
1974 John Ostrom resurrects the
idea that birds evolved from dinosaurs
—an idea that had been dormant for
a century.
1980 Louis and Walter Alvarez put
forward the asteroid impact theory of
dinosaur extinction.
1985 Discovery by scientists of the
British Antarctic Survey of the
depletion of ozone in the upper
atmosphere.
1988 Hottest northern hemisphere
summer on record brings public
awareness of global warming.
1991 Chicxulub crater in Yucatan is
pinpointed as the site of the impact
that may have caused the dinosaur
extinction.
1992 Joe Kirschvink suggests the
snowball Earth theory—that the Earth
was covered by ice during the
Precambrian.
TIMELINE OF THE HISTORY OF GEOLOGY AND PALAEONTOLOGY
WILLIAM SMITH
Dates: 1799–1847
Nationality: British
Best known for: Mary Anning
was a professional fossil collector,
working from the beaches of
Dorset and Devon in the south of
England. She began work when
she was 12 years old to support
her family after her father died.
Mary Anning is credited with
finding the first complete fossil at
the age of just 12 on the beach of
Lyme Regis. She supplied fossils
for all the eminent scientists of
the day.
Key discoveries: The first full
skeleton of an ichthyosaur and
also of the first plesiosaur.
610–425 BC Philosophers Thales,
Anaximander, Pythagoras,
Xenophanes, and Herodotus recognize
that fossils show that the distribution of
land and sea was once different.
fossils are remains of animals and
their enclosing rocks must have been
lifted from below sea level.
1542 Leonhart Fuchs publishes a
cataloge of 500 plant species.
1546 Georgius Agricola (born
George Bauer, 1494–1555), “Father
of mineralogy,” classifies minerals by
their crystal shape and composition.
Publishes an analysis of ore bodies.
1585 Michele Mercati opens the first
geological museum.
1596 Dutch cartographer Abraham
Ortelius first suggests continental drift.
1600 William Gilbert, Elizabeth I’s
physician, describes the Earth’s
magnetism.
1616 Italian philosopher Lucilio
Vanini first to suggest humans
descended from apes. He was
executed for this belief.
1641 Lawyer Isaac La
Peyrère suggests that
people existed before
Adam and Eve. His
ideas were only
published after
his death.
1658 Jesuit missionary Martino Martini
shows that Chinese history predates the
above. Nobody takes notice.
1668 Robert Hooke claims that Earth’s
movements, and not the biblical Flood,
moved fossils to dry land.
1669 Nicolaus Steno (born Neils
Stensen, 1638–86) establishes the
laws of stratigraphy, which state that
rock beds laid down horizontally,
stacked on one another, and
subsequently contorted.
1679 Scandinavian historian Olof
Rudbeck tries to date sedimentary rocks.
1688 The Ashmolean Museum opens
in Oxford—the world’s first public
museum.
1715 Edmund Halley suggests the
age of the Earth can be calculated
from the salinity of the seas.
1735 Linnaeus establishes the
binomial classification of living things.
1745 Mikhail Vasil’evich Lomonosov
(1711–65) recognizes that ancient
geological processes would have been
similar to today’s, in anticipation of
James Hutton (see 1795 ).
1749 Georges-Louis Leclerc de
Buffon speculates that the planets
formed by a comet crashing into the
sun. The people in power force him to
retract it.
1751 Diderot and d’Alembert publish
the first encyclopaedia—with a
reliance on factual information rather
than on traditional beliefs.
1760 Giovanni Arduino classifies the
geological column – Primary: with no
fossils, Secondary: deformed and with
fossils, Tertiary: horizontal and with
fossils, and Quaternary: loose sands
and gravels over the rest. This was a
rough basis of modern classification.
1766 Torbern Olaf Bergman
(1735–1784) sees that different rock
types were formed at different times
and appreciates the organic origin of
fossils.
1768 James Cook’s voyage brings an
awareness of the range of plants and
animals around the world to the
United Kingdom.
Dates: 1769–1839
Nationality: British
Best known for: William Smith
observed the rocks of Britain in his
role as a canal engineer, and
realized that the same layers, or
beds, of rocks could be traced over
large areas by using their fossils to
identify them. He eventually used
this knowledge to compile the first
ever geological map, where
mainland Britain was colored
according to the rock types.
Key discoveries: The principle
of faunal succession, in which the
same rocks can be identified by
the fossils they contain, wherever
they occur.
1780 Abraham Gottlob
Werner (1749–1817)
theorizes that all rocks are
formed in ancient oceans.
He is wrong but greatly
influential.
Dates: 1840–97
Nationality: American
Best known for: Edward Drinker
Cope was one of the first
vertebrate palaeontologists in
America and was affiliated with
The Academy of Natural Sciences
in Philadelphia. His arrogance
drove him to fall out with Othniel
Charles Marsh, instigating the
“bone wars.” This event
stimulated the discovery of
dinosaurs, but drove more
methodical workers away
from the science.
Key discoveries: About 65 new
dinosaur genera.
CHARLES DOOLITTLE WALCOTT
Dates: 1850–1927
Nationality: American
Best known for: Walcott worked
for, and became the director of, the
US Geological Survey. He was a
vertebrate palaeontologist and
worked mostly in the Cambrian of
the United Sates and Canada. He
later became the Secretary of the
Smithsonian Institution and was one
of the most powerful figures in the
American scientific community.
Key discoveries: The discovery
of the Burgess Shale and its variety
of fantastic Cambrian fossils.
about dinosaurs, early reptiles, amphibians, and mammals. Every page is packed with names,
statistics, and key pieces of information about the history of Earth. For fast access to just the
facts, follow the tips on these pages.
Crick and Watson
GEORGES CUVIER
OTHNIEL CHARLES
MARSH
CHARLES DARWIN
Calcite – a common mineral
78 BC Pliny the Elder writes the first
natural history encyclopaedia.
c AD 1000 Al-Beruni (973–1050)
observes that different grades of
sediment is deposited by different
strengths of river currents—an early
observation of sedimentology. He also
puts precious minerals into
geological context.
1020 Avicenna (or Sina)
observes the work of erosion.
1056 Albertus Magnus publishes
a book on minerals.
1500 Leonardo da
Vinci states that
1953 Stanley Miller and Harold Urey
combine the gases of the Earth’s initial
atmosphere and form the chemicals
from which living things are made.
1953 James Watson and Francis
Crick determine the molecular
structure of DNA.
1953 Fiesel Houtermans and Claire
Patterson use radiometric dating to
date the Earth at 4.5 billion years old.
Dates: 1769–1832
Nationality: French
Best known for: Georges Cuvier
was one of the most influential
figures in science of the time,
particularly in the field of anatomy.
He is regarded as the father of
vertebrate palaeontology. He
refused to acknowledge evolution
and resisted the popularization of
scientific knowledge.
Key discoveries: Classified all
living and fossil things according
to their similarity to one another,
as we do today.
1800 Lamarck proposes
a theory of evolution.
It suggested that traits that
are acquired in life can
be passed on to the next
generation. This is no
longer accepted since the
general acceptance of
Darwin’s theory of natural
selection.
The Earth’s magnetism
1771 Joseph Priestley discovers
oxygen and shows its importance to
life.
1778 Buffon puts the age of the Earth
at 74,832 years.
1789 French researcher Antoine
Lavoisier interprets different
sedimentary rocks as showing different
sea levels in the past.
1795 James Hutton, the “Founder of
modern geology,” sees geological
processes as a cycle, with no
beginning and no end.
1799 Alexander von Humboldt
names the Jurassic system.
1799 British surveyor William Smith
produces the first geological map,
establishing the importance of fossils
to define rocks and times.
1804 Cuvier acknowledges that fossil
animals are older than can be
explained by the Bible and suggests
previous cycles of creation and
destruction.
• See page 30–31
ICHTHYOSAURS
ALFRED WEGENER
SIR CHARLES LYELL
Dates: 1880–1930
Nationality: German
Best known for: Alfred Wegener
was a meteorologist, doing a
great deal of work in Greenland.
He advocated the concept of
continental drift, calling it
continental displacement
when he first lectured on it in
1912, although he could not
think of a mechanism that would
account for the phenomenon.
He died in an accident on the
Greenland ice cap.
Key discoveries: Proposing
continental drift as a serious
scientific idea.
Dates: 1797–1875
Nationality: British
Best known for: Sir Charles
Lyell was a field geologist who
published a ground-breaking
work The Principles of Geology. It
explained the observed geological
phenomena in terms of scientific
actions rather than the works of
God. He stressed that the human
species must have been older
than currently believed.
Key discoveries: Establishing
the geological column, with time
divided into periods.
Dates: 1831–99
Nationality: American
Best known for: Professor of
palaeontology at Yale University
and curator of the Peabody
Museum of Natural History. He
was a rival of Edward Drinker
Cope, and their animosity resulted
in the “bone wars,” when each
tried to discover more than the
other.
Key discoveries: About 80 new
genera of dinosaurs, establishing
the vastness of fossil life.
James
Cook
Dates: 1809–82
Nationality: British
Best known for: After failed
attempts at careers in medicine and
the church, he became a naturalist.
His famous voyage on HMS Beagle
allowed him to observe and collect
examples of flora and fauna from all
other the world. He built on the
already existing ideas of evolution
and deduced the mechanism
involved.
Key discoveries: The idea of
natural selection as the force that
drives evolution.
TIMELINES
A breakdown of the names given to
the different subdivisions of time.
BOX HEADINGS
Look for heading words linked to your
research to guide you to the right fact box.
1862 Lord Kelvin suggests
that the Earth is 20–400
million years old, based
on rates of cooling.
A 50,000-year-old crater
shows that the Earth is still
being bombarded by meteors.
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53
54
55
INTRODUCTION TO TOPIC
52–53 Uncovering the Prehistoric World Timeline
54–55 Key Figure Biographies
TWO QUICK WAYS
TO FIND A FACT:
EARLY PALEOZOIC ERA
THE BURGESS SHALE
ANIMAL
PROFILES
PICTURE CAPTIONS
Captions explain what is in the pictures.
EARLY
PALEOZOIC
TIMELINE
D uring the early Paleozoic era, many different kinds of hard-shelled
The most spectacular set of
Cambrian fossils lies in the
Burgess Shale in Canada. These
consist of all kinds of animals,
most of which do not fit into any
established classification.
Burgess shale animals
Marella – like a trilobite with long
horns on its head.
Nectocaris – like a shrimp’s body
with an eel’s tail.
Opabinia – like a worm with a
trunk and many pairs of paddles.
Wiwaxia – like a slug covered in
chain mail.
Hallucigenia – a worm-like body
with tentacles along one side and
stilts along the other.
Anomalocaris – a big swimming
predator that probably hunted
all these.
ANIMAL PROFILES
Different animals’ statistics are
listed here.
For fast access to facts about different
animals, look for the name in
the headings.
animals have evolved in the sea. By the end of the early Paleozoic,
however, some life was beginning to venture out of the water and
live on dry land.
1
Look at the detailed CONTENTS list on
page 3 to find you
topic of interest.
543–417 MYA
Pridoli
Ludlow
Wenlock
Llandovery
Bala
Silurian
• See page 55 for
more information on CHARLES
DOOLITTLE WALCOTT who
discovered the Burgess Shale.
SILURIAN PERIOD
Meaning: From Silures – an old
Welsh tribe.
Continents were continuing to
move together. The edges of the
continents were flooded, giving
large areas of shallow sea over
continental shelves. Many reefs
and shallow-water organisms existed
at that time. The first
land-living plants appeared.
The Burgess Shale in Canada today.
Ordovician
Dyfed
Canadian
Isotelus
Period: Silurian
Diet: Buried organic
matter
Habitat: In sandy sea
bottoms
Information: Spade-shaped
trilobite, smooth surface,
adapted for burrowing.
Cryptolithus
Period: Ordovician
Diet: Floating
organic matter
Habitat: Open water
Information: Free-swimming
trilobite, huge cephalon
with long spines at the
rear, small thorax and
pygidium.
Eodiscus
Period: Cambrian
Diet: Floating organic
matter
Habitat: Open water
Information: Tiny early
trilobite, free swimming,
only two segments in the
thorax, cephalon the
same size as pygidium.
Olenellus
Period: Cambrian
Diet: Organic detritus
Habitat: Shallow sea
bed
Information: An early
trilobite, tiny pygidium,
spines on the segments.
Isotelus
Cambrian
Merioneth
St David’s
Caerfai
PALAEOZOIC ERA
GLOSSARY
• A GLOSSARY of words and terms
used in this book begins on page 58.
The glossary words provide additional
information to supplement the facts on
the main pages.
Turn to the relevant
page and use the BOX HEADINGS to find the
information box you need.
The Palaeozoic era is
made up of six periods.
The first three periods make up
the early Palaeozoic era. the
other three are the Devonian,
Carboniferous, and Permian.
ORDOVICIAN PERIOD
Meaning: From Ordovices –
an old Welsh tribe.
In the Ordovician period, the
northern landmasses were
beginning to move toward one
another. An ice age took place
at the boundary with the Silurian,
450 to 440 million years ago.
CALYMENE
2
Turn to the INDEX which starts on page
60 and search for key words relating to
your research.
• The index will direct you to the correct page,
and where on the page to find the fact
you need.
Permian 290–248 MYA
Time : Silurian
Size : About 1 3
Pygidium – tail shield made
from fused segments
Carboniferous 354–290 MYA
⁄ 16 in.
Diet : Organic particles from
sea bed
Habitat : Shallow seas
Information : Calymene was
a typical trilobite—one of the
most abundant of the sea-living
arthropods in the early Paleozoic.
Thorax – central
part of body made
up of segments
Devonian 417–354 MYA
early Palaeozoic 543–417 MYA
Cephalon –
head shield
LINKS
Look for the purple links throughout the
book. Each link gives details of other
pages where related or additional facts
can be found.
LAND ANIMALS
Although we believe there were
no land animals in the early
Paleozoic, some strange trace
fossils from Canada, from the
Cambrian period have been
found.
They were made by a soft-bodied
animal. The animal moved along
the damp sand of the Cambrian
shoreline. The animal had flaps on
either side of its body and dug
those into the sand to pull itself
forward, creating tracks that look
like motorcycle tracks.
CAMBRIAN PERIOD
Meaning: From Cambria – an old
name for Wales, where the original
work was done on the lower
Paleozoic rocks.
In the early Paleozoic, all of the
southern continents, South America,
Africa, India, Australia and
Antarctica, were part of a single
landmass. The northern continents,
North America, Europe, and Asia,
were individual landmasses
scattered over the ocean.
DIPLOGRAPTUS
Time: Silurian
Size: 2 in., each branch
Diet: Suspended organic particles
Habitat: Open water
Information: Diplograptus was a
common graptolite—a floating
colonial organism. It consisted of
two rows of living creatures back to
back, and several hanging
suspended from a gas float.
Other graptolites include
Monograptus, with a single row of
individuals, and Didymograptus, with
two rows arranged in a wishbone
shape. These are all valuable index
fossils for the early Paleozoic.
• See pages 12–13 for more
information on INDEX FOSSILS.
• See pages 12–13 for more
information on index fossils.
16
17
JUST THE FACTS
Each topic box presents the facts you
need in short, quick-to-read bullet points.
ANIMAL FEATURES
A more detailed study of an animal of the time. A picture
accompanies the information to give a better idea of what life was
like at that time.
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5
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THE PRECAMBRIAN EON 4,500–543 MYA
THE AGE OF
HOW DO WE
KNOW?
OLDEST MINERALS, ROCKS, AND METEORITES
PREVIOUS ESTIMATES OF
THE AGE OF THE EARTH
The Precambrian eon covers
three eras and over 4,000
million years. However, during
this period, primitive lifeforms
were only starting to develop,
and it wasn’t until later that life
truly began to take shape as
we know it.
Proterozoic 2,500–543 MYA
Archaean 3,800–2,500 MYA
Hadean
The oldest minerals – 4.3
billion years old. They were
found in much younger
sedimentary rocks in Australia.
The oldest rocks – 4.03
billion years old found in
the Great Slave Lake in
northwestern Canada (shown
below). These are metamorphic
rocks and are formed from
rocks that already existed and
must have been older.
THE EARTH
T he Earth is
We can look at
radioactive minerals
in rocks.
Radioactive minerals
change at a regular rate
over time. By looking at
the amount of radioactive
mineral that has changed,
we can figure out how
long the changes have been
going on, which provides
the length of time since
the mineral was formed.
• About 5 or 6 thousand years – Going
by the dates in the Bible and universally
accepted until about 150 years ago.
• 25–40 million years – Lord Kelvin in
1862 . He based his calculation on how long
the Earth would take to cool to its present
temperature assuming that Earth began hot
and molten. He did not know about radioactivity.
Radioactivity continues to generate heat, so
the Earth cools much more slowly.
• Irish Geologist Samuel Haughton in
1878 suggested that the age could be
estimated by measuring the depth of
sedimentary rocks.
• 27.6 million years – Walcott in 1893 .
• 18.3 million years – Sollas in 1900 . Both
he and Walcott were influenced by Haughton.
• 704 million years – Goodchild in 1897 .
• 96 million years – John Joly in 1889 .
He was working on the rate of buildup of
salt in the ocean.
4,500–3,800 MYA
The oldest meteorites – 4.6
billion years ago. They are
assumed to have formed at the
same time as Earth.
about 4.6 billion
years old.
During that time, there
have been extreme
changes in layout of the
land and the oceans, as well
as vast differences in the kinds of life that have
walked on Earth’s land, flew in its sky, and
swam in its seas. While everything looks to be
stable in our eyes, the Earth is constantly
changing, continents are moving, and life
continues to change.
This is what the surface of the Earth may have looked like
whe it was still forming in the Hadean era.
Early Paleozoic 543–417
Devonian 417–354
Carboniferous 354–290
Permian 290–248
Triassic 248–206
Jurassic 206–144
Cretaceous 144–65
Tertiary 65–1.75
Quaternary 1.75–present
PHANEROZOIC EON
TO PRESENT DAY
The Phanerozoic eon covers three
eras: the Paleozoic, highlighted in
GREEN , the Mesozoic,
highlighted in PURPLE, and the
Cenozoic, highlighted in RED .
Each one of these are then
subdivided into different periods as
noted. Although the Phanerozoic
eon is only 543 million years, it
covers the period when life
advances on Earth.
The First Reptiles
In the Carboniferous period,
life on land was fully established.
The coal forests are filled with giant
insects and the first reptiles.
The forests eventually formed
the coal we use as fuel today.
GEOLOGICAL TIME
SCALE
First Signs of Life on Land
In the early Paleozoic period, life was
predominantly sea-based. Hard-shelled
animals were evolving at this time. By
the end of the period, life was starting
to venture onto the land.
The Reptiles Flourish
Between the Permian and Triassic
periods, there was another mass
extinction. This brought about a spurt
in the development of lifeform. The
first dinosaurs appeared on Earth.
The Age of Dinosaurs Begins
Dinosaurs evolved in the late Triassic
period and ruled the Earth until the
end of the Cretaceous period. As the
continents moved apart, newer and
more fantastic dinosaurs evolved on
the separate continents.
The Great Extinction
At the end of the Cretaceous period,
a cataclysmic event occured
that wiped out all the dinosaurs,
pterosaurs, and sea reptiles.
This cleared the way for the first
mammals.
The Age of Mammals
After nearly all of life is wiped out by
the Great Extinction, the Early Tertiary
period sees life on Earth taking new
direction. Gone are the dinosaurs and
great pterosaurs that ruled the sky,
new creatures that graze on the
newly developing grass and plants
thrive during this time.
Human Beings First Appear
Human beings first appeared about
200,000 years ago. Earth begins to
look more and more like it does now.
• When the geological time scale
is shown vertically the oldest
division is always at the bottom
and the youngest, or the
present day, is at the top.
• This reflects the sequence in
which sedimentary rocks are
laid down (see p10–11).
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