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BiologyPreliminary CourseStage 6

Life on Earth

Part 2: Origin of life

Incorporating October 2002

AMENDMENTS

Part 2: Origin of life 1

Contents

Introduction................................................................................ 2

Fossils ...................................................................................... 4

Types of fossils ....................................................................................5

Formation of fossils..............................................................................7

Evolution of living things .......................................................... 10

Membranes.........................................................................................10

Procaryotic cells .................................................................................11

Eucaryotic cells ..................................................................................14

Colonial organisms ............................................................................15

Multicellular organisms ......................................................................15

More about the appearance of life ........................................... 16

Palaeontological evidence.................................................................16

Geological evidence...........................................................................17

Scientific discoveries and belief systems................................. 21

Technological advances ....................................................................21

Scientific beliefs .................................................................................22

Additional resources ................................................................ 25

Suggested answers ................................................................. 27

Exercises – Part 2 ................................................................... 29

2 Life on Earth

Introduction

The fossil record provides information about the subsequent evolution of

living things. The first organisms on the Earth were probably

heterotrophic procaryotes. Once photosynthesis began, free oxygen

became available leading to more efficient aerobic respiration and the

formation of the ozone layer thus reducing the amount of ultraviolet

radiation hitting the Earth.

Part 2 will provide you with opportunities to learn to:

• identify the major stages in the evolution of living things, including

the formation of:

– organic molecules

– membranes

– procaryotic heterotrophic cells

– procaryotic autotrophic cells

– eucaryotic cells

– colonial organisms

– multicellular organisms

• describe some of the palaeontological and geological evidence that

suggests when life originated on Earth

• explain why the change from an anoxic to an oxic atmosphere was

significant in the evolution of living things

• discuss the ways in which developments in scientific knowledge

may conflict with the ideas about the origins of life developed by

different cultures.

Part 2 will provide you with opportunities to:

• process and analyse information to construct a timeline of the main

events that occurred during the evolution of life on Earth

• gather first-hand or secondary information to make observations of a

range of plant and animal fossils


• identify data sources, gather, process, analyse and present

information from secondary sources to evaluate the impact, of

increased understanding of the fossil record on the development of

ideas about the history of life on Earth.

Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originally

issued 1999. Revised October 2002. The most up-to-date version can be

found on the Board’s website at

http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html.

4 Life on Earth

Fossils

The question of how life originated on Earth still puzzles scientists.

However, the kinds of life forms present on the Earth over the last

3.8 billion years can be more clearly understood because information

about ancient life is preserved in rocks as fossils.

Fossils are the traces or remains of living things that have been

preserved. The study of fossils is called palaeontology, and people who

study the history of living things in this form are called palaeontologists.

The fossil record has been used to interpret the history of life on Earth

and used as evidence to infer the possible past climates and life forms in

different regions. Fossils provide evidence that life has changed

throughout the history of the Earth. This gradual change is what the term

evolution refers to. The word is derived from evolutus, which

means ‘unrolling’.

The idea of evolution is simply one of change. The theory of evolution

states that organisms living today are the descendants of ancient forms of

life which have changed gradually over time. This means that the

organisms undergo genetic changes or become genetically different as

time passes. As with any theory in science, the theory of evolution is

based on scientific evidence.

Keep in mind that scientific theories are based on the evidence available

at the time that they are proposed. They remain liable to review and

subsequent revision, such as the example in Part 1, outlining the theory

of spontaneous generation from the Middle ages.

For a theory to maintain its place within the scientific community, the

evidence on which it is based and the predictions that arise from it must

be subjected to and withstand scientific scrutiny. Scientists debate the

details of the processes and mechanisms of evolution. This is because

different views are a part of the investigative nature of science.

Generally, the evidence for evolution and the broad mechanism of

natural selection by which evolution occurs are generally accepted by

the scientific community.


Types of fossils

When you think about the word fossil, what images do you think of?

Fossil A: brachiopods. (Photo: ©LMP.)

Fossil B: fish. (Photo: Monika Khun ©LMP.)

Fossil C: Glossopteris. (Photo: Monika Khun ©LMP.)

6 Life on Earth

Fossil D: Ammonites. (Photo: Monika Khun ©LMP.)

Fossil E: Trilobite. (Photo: ©LMP.)

1 Many fossil organisms are similar to organisms living today. Can you

identify an organism that is similar to each of the fossils pictured?

You may have seen some of these fossils in your previous studies.

A ____________________________________________________

B ____________________________________________________

C ____________________________________________________

D ____________________________________________________

E ____________________________________________________


2 Describe how one of these fossils may have formed.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

Check your answers.

If you would like more information, look at the LMP web site for links to

fossil sites.

http://www.lmpc.edu.au/science

The formation of fossilsFossils are formed in a number of different ways, depending on the

physical conditions in the area and the type of material being preserved.

Even the most delicate insects can be preserved given the right

conditions. Single-celled organisms and even jellyfish have been found

preserved in rocks, although these are rare.

Generally the key elements required for fossil formation are: a quick

burial, no decay and the remains left undisturbed.

1 Suggest why these elements might be necessary for fossil formation.

_____________________________________________________

_____________________________________________________

_____________________________________________________

2 Predict the body parts of organisms that are most likely to be

preserved under these conditions.

_____________________________________________________

_____________________________________________________

_____________________________________________________

8 Life on Earth

3 Look at the following pictures depicting the formation of a fossil.

What is the correct sequence for the formation of the fossil?

recent sediment

fish skeleton partly buried by sediment

more recent sediment

fish skeleton fossilised in oldersedimentary rock

sedimentary rock exposed geological fault exposes fossil

The correct sequence of events, in order is, ________________________

Check your answers.

The fossil record relates to evidence that present day organisms have

developed from different organisms in the past.

i) lobe finned

fish (Devonian)

ii) amphibian

(Carboniferous)

A comparison of animals from the Carboniferous and Devonian era


The lobe-finned fish and a carboniferous amphibian show a gradual

change in structure of the limbs. This is an example of an organism that

has evolved from different ancestors in the distant past.

Complete Exercise 2.1: Fossil evidence.

10 Life on Earth

Evolution of living things

The current scientific thinking is that the major stages in the evolution of

life are Earth are:

• organic molecules

• membranes

• procaryotic heterotrophic cells

• procaryotic autotropic cells

• eucaryotic cells

• colonial organisms

• multicellular organisms.

You have seen from Part 1 that the early Earth was suitable for the build

up of organic molecules. From this point, the next stage was the

formation of a membrane to contain the organic molecules.

Membranes

Cell membranes are very important for living things as they perform the

function of containing and protecting the organic molecules within.

The function of a membrane is to control the movement of materials

between the internal and external environments. One quarter of the

energy used by cells is designated to this function.

The existence of a cell membrane is an advantage to a molecule because

it separates the internal and external environment. This makes it possible

for different substances to be present and enables life processes to occur.

Macromolecules (large molecules) would have difficulty reproducing

unless they were surrounded by membranes that prevent the loss of

materials to the surroundings. This protection is another advantage of the

presence of membranes.


When did a membrane-bound unit become a cell? A membrane-bound

unit became a cell around 3.8 billion years ago. This simple unit

developed the ability to survive and reproduce independently–the

first cell.

Procaryotic cells

The first cell to form was a procaryotic cell. Procaryotes are simple one-

celled organisms. They differ from other cells (eucaryotes) in that they

have no internal membrane-bound organelles. Procaryotes can be:

• heterotrophic or

• autotrophic.

This refers to how they feed. Autotrophic organisms have the ability to

make some of their own nutrients while heterotrophic organisms rely on

external sources for nutrients.

Procaryotes are still the most abundant form of life on the Earth.

Heterotrophic procaryotic cells

The earliest procaryotic cells would have been heterotrophic.

Nutrients were probably absorbed in a form that did not require

conversion. These cells utilised nutrients such as carbohydrates, amino

acids and other organic compounds in their environment. Few complex

biochemical reactions would have taken place within these

simple organisms.

Gradually, as the nutrients were depleted, the competition between the

organisms would have increased. Those organisms that were inefficient

at obtaining nutrients would have disappeared and only those that were

able to most efficiently obtain nutrients would survive. It follows then

that natural selection would have favoured any changes or mutations in

an organism that enhanced its ability to gain nutrition.

For example, organisms capable of biochemical reactions to synthesise

materials required to sustain living process would be advantaged.

Some organisms may have developed alternate methods of obtaining

nutrition such as parasitism, predation, or saprophytism, however life

could not have continued indefinitely under such conditions.

12 Life on Earth

Predict why life would have ceased to exist if all organisms were

heterotrophic?

_________________________________________________________

_________________________________________________________

Check your answer.

Autotrophic procaryotes

While heterotrophic cells are thought to be the first form of life, the

evolution of autotrophic organisms has had far reaching effects.

These effects include the presence of free oxygen in the atmosphere and

the start of the ozone layer which reduced the amount of ultraviolet

radiation hitting the Earth’s surface.

The continuation of life is a result of the development of simple

photosynthetic pathways by some autotrophic organisms, such as the

Cyanobacteria. The production of oxygen by these organisms as a waste

product of photosynthesis assisted in the conversion of a reducing to an

oxidising atmosphere.

Photosynthesis is thought to have commenced over three billion years

ago and in a two billion year interval the process completely altered the

chemistry of the Earth and the surrounding atmosphere.

Oxygen reacts readily with other elements and compounds. The first

major reaction was possibly between seawater and iron to form iron

oxide. Oxygen also reacts with ammonia to form nitrogen and water.

Carbon dioxide can be produced from methane.

These reactions resulted in the reduction of minerals exposed to

oxygen in the atmosphere or hydrosphere to their oxides. After this,

free molecular oxygen began to accumulate and was available

for respiration.

It is a generally accepted fact that life began in aquatic environments and

then moved to land. The atmosphere gradually changed from an anoxic

to oxic one, as the levels of oxygen increased from photosynthesis.

The presence of free oxygen supported the process of respiration which

was a more efficient way of gaining energy.

The next important product resulting from the accumulation of oxygen

was the ozone layer. The ozone layer absorbs most of the Sun’s

ultraviolet radiation, preventing it from reaching the Earth’s surface.

Ultraviolet radiation is harmful to life. Without the ozone layer, life

could only exist underwater. This is thought to be the reason why both


plants and animals were thought to move onto land (terrestrial

environments) around the same time, approximately 350 million

years ago.

What relationship do you think existed in the movement of living things

from water to land and the increasing amount of ozone?

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.

Once the layer of ozone formed around the atmosphere the ultraviolet

radiation reaching the surface was decreased. The organisms had

changed the conditions on early Earth to such an extent that it became

impossible for some of the earliest life forms to remain in existence.

The presence of oxygen resulted in the development of aerobic

respiration in both heterotrophic and autotrophic organisms, making

energy production far more efficient.

Change from anoxic to oxic conditions

What were the differences in the conditions that existed in the early

atmosphere and the present atmosphere that you recall from Part 1?

The early atmosphere was called an anoxic atmosphere due to the

absence of oxygen. The present atmosphere is described as an oxic

atmosphere, which means there is oxygen present. As the amount of free

oxygen increased (oxygen not bound to other elements in a compound) it

was possible for aerobic organisms to survive. This probably did not

occur in the atmosphere until the advent of photosynthetic organisms.

In photosynthesis, oxygen is released after carbon dioxide has combined

with water using the energy from sunlight.

As the carbon dioxide is taken up and used in the process of

photosynthesis the concentration of carbon dioxide in the

atmosphere decreased.

The earliest known photosynthetic organisms are the cyanobacteria.

These very primitive, single celled organisms have been found in rocks

dating back to about 3465 million years ago. The release of oxygen into

the atmosphere increased dramatically with the advent of the

photosynthetic algae that first appeared approximately 1500 million years

ago. It was from this point on that the atmosphere became abundant in

free oxygen and could be referred to as an oxic atmosphere. This made it

possible for a rapid expansion in types of eucaryotic organisms.

14 Life on Earth

Eucaryotic cells

A eucaryotic cell has membrane-bound organelles within it. The origin of

eucaryotic cells is still uncertain. However, it is agreed that eucaryotic

cells are far more complex than the procaryotic cells from which they

may have evolved. Generally it is believed that there must have been

many evolutionary steps involved in the transformation.

The best estimates for this transformation range from approximately

1.5 billion years to 3.5 billion years before present. A typical eucaryotic

cell is thought to have resulted from symbiotic relationships between

different procaryotic ancestors. This means that procaryotic organisms

combined together in a relationship with benefits for both organisms.

Organelles such as chloroplasts and mitochondria contain their own

DNA and are thought to be once free-living procaryotic organisms that

have become enclosed in other cells.

originalprocaryotic

host cell

DNAchromosomes

aerobicbacteria

multipleinvaginations ofcell membrane

protoeucaryotecompoundorganism

the bacteriabecome

mitochondria

endoplasmicreticulum and nuclearmembrane form fromthe cell membrane

invaginations

eucaryoticplants and

some protists

eucaryoticanimals, fungi

and someprotists

photosyntheticbacteria

the photosyntheticbacteria become

chloroplasts

Eucaryotic cell development

Thus, symbiotic relationships between bacteria containing these

components eventually gave rise to the eucaryotic cells with membrane

bound organelles. This is called the endosymbiont theory. However, it

does not explain how the genetic material in the nucleus became

surrounded by a membrane.


Colonial organisms

The next stage in the evolution of life on Earth involved simpler

organisms combining together to form colonial animals.

Colonial organisms are an association of organisms in which the

individuals are connected. Colonial organisms may have originated

from the aggregation (sticking together) of similar daughter cells after

cell division. Fossil evidence for such colonies can be seen in the

stromatolites. Present day stromatolites are still found as

colonial structures.

Multicellular organisms

As organisms continued to develop and change, multicellular organisms

containing cells with specialised or differentiated function evolved.

Similar cells group together in tissues. Different tissues form organs

that work together in a coordinated fashion in higher order plants

and animals.

Complete Exercise 2.2: Evolution of life on Earth.

16 Life on Earth

More about the appearance of life

Geology (the study of rocks and landforms) and palaeontology (the study

of fossils) provide evidence about past events and conditions on Earth.

They provide a permanent record that can be used to identify when life

originated and how life has evolved.

Palaeontological evidence1 What is palaeontology?

_____________________________________________________

_____________________________________________________

2 How do you think a study of palaeontology provide evidence about

the appearance of life on Earth?

______________________________________________________

______________________________________________________

Check your answers.

Scientists are able to use palaeontological evidence (evidence from

palaeontology) to help predict the conditions on Earth and the time when

life originated. As well as the large fossils that you would be used to

seeing they is much to be learned from less obvious fossils.

Early fossils

The origin of life is currently estimated at about 3.8 billion years ago

because this is the approximate age of the oldest known fossils.

Early fossils are rare and include:

• microfossils such as foraminifera and


• stromatolites.

Microfossils – foraminifera

Foraminifera are marine single-celled protozoans that have a calcium

carbonate shell. Oxygen isotopes are locked up in the shells of these

microfossils. Fossils foraminifera are abundant in some sediments and

are used as an indicator of past climate change. They are also used to

age deposits.

Foraminifera. (Photo: Courtesy of NASA)

Stromatolites

Stromatolites are made by cyanobacteria. Their fossils are found in rocks

in Western Australia dated at 3.5 billion years old. To put this in

perspective, the oldest rocks on Earth are 3.8 billion years.

They are photosynthetic so they released oxygen into the atmosphere as a

waste product. This played an important role in the changes that

occurred in the atmosphere that lead from an anoxic to an oxic

atmosphere. As well as putting oxygen into the atmosphere they

removed carbon dioxide from the surrounding water which started the

precipitation of calcium carbonate. This is caught in the sticky mucilage

around the cyanobacteria and over time builds up into sediments.

More about stromatolites later.

Geological evidence

Geological evidence (evidence from rocks and landforms) can also

provide information about the conditions present and timing of the origin

of life. For example, the early atmosphere is described as anoxic,

meaning there was very little free oxygen. The oxygen that did exist was

‘locked up’ with other elements as compounds. Ancient rocks contain

many oxides, such as iron (II) oxide (FeO2) and aluminium oxide

18 Life on Earth

(Al2O3). There is evidence that water (H2O) was plentiful, but there is

not evidence in ancient rocks of free oxygen.

Banded iron formations (BIFs)

BIF stands for banded iron formation. At the time of the formation of

these deposits the atmosphere did not contain free oxygen and the sea

contained large amounts of dissolved iron. When the first organisms

began to photosynthesise they gave off oxygen as a waste product.

This oxygen was immediately bonded with dissolved ferrous ions (iron

(II) ions ) and formed insoluble ferric oxide (iron oxide). This is the

same process that we call rusting. The sediments fell to the bottom and

the banded iron formations were formed by alternative layers of iron rich

material and silica-rich chert.

A BIF sample showing layering. (Photo Ric Morante.)

Deposits such as those found in the Hamersley Ranges in Western

Australia (which make up the world’s largest iron ore deposit) were

deposited in ancient aquatic environments more than 1700 million

years ago.

BIFs could not be deposited in the oceans of today as dissolved oxygen

(II) ions, would quickly react with the iron to oxidise it into the iron (III)

(Fe3+

) state. The iron would then be transformed into orange-red iron

oxide. At the time of formation of BIFs the soluble iron in seawater

‘soaked up’ any available oxygen and free oxygen could not become

available until all of the available unoxidised iron was oxidised.


A sample of rock, dated at approximately 3.2 billion years, comes from a

banded iron formation.

What evidence does the sample provide about the conditions that may have

existed 3.2 billion years ago?

_________________________________________________________

_________________________________________________________

Check your answer.

Uraninite

Another piece of evidence of this early anaerobic atmosphere comes

from the study of uraninite (uranium dioxide, UO2). This mineral no

longer accumulates as a free particle to be washed down streams and

deposited in sediments. Why? Because when uranium dioxide is

exposed to excess oxygen, uranium oxide (U3O8) is formed.

The following equation shows the chemical reaction. The oxygen on the

left-hand side of the equation would exist as ‘free’ oxygen in the

atmosphere for this reaction to proceed.

3UO2 + O2 U3O8

uranium dioxide + oxygen uranium oxide.

Massive deposits of uraninite, which were deposited as long as 2.3

billion years ago, have been found in South Africa and Canada. The fact

that they could be deposited as sediments suggests that they did not react

with oxygen. This therefore, is good evidence of an oxygen

deficient environment.

A timeline is a good tool to use to put all of this information into

perspective. Your task is to construct a timeline of the main events that

occurred during the evolution of life on Earth. The table in the Additional

resources section is a good starting point for your timeline.

a) Plan your timeline.

What information will you include?

Do you require extra information? How or where will you

obtain it?

How will you present the information?

What materials do you need?

20 Life on Earth

b) Collect and organise the resources you need. Analyse the

information you have collected to identify the events that you

will include on your timeline.

c) Complete your timeline on your own paper and send it to your

teacher as Exercise 2.3.

d) Draw a blue line across the list at the point where you think the

biological idea of life first began.

Draw a green line across the list where Earth’s atmosphere

would have begun changing from anoxic to oxic.

Complete Exercise 2.3: Evidence for the origin of life.


Scientific discoveries andbelief systems

You have examined some of the evidence that scientists have used to

deduce the age and conditions on Earth, as well as the origins and

evolution of life on Earth. Now you will focus on the technology and

changes in technology, that have assisted scientists in developing the

current view of the history of the Earth and of life on Earth.

Technological advances

In Part 1 you looked some technologies that were used to identify the

possible age of rocks and organic remains as well as technology used to

identify correlation between organic molecules. In this part you looked

at the evidence used to identify when life originated on Earth.

Fossils have been used extensively to determine the conditions on Earth

in the past. Microfossils, such as foraminifera, are very small and require

the use of microscopes such as electron microscopes to enable detailed

comparison. Other fossils that can be used include spores and pollen as

they have very specific periods of existence, which makes them ideal to

use as indicators of climatic conditions and atmospheric evolution.

Microfossils have been obtained from under the ocean, polar regions and

continental landmasses. Other core samples have been taken from

terrestrial impact and explosion craters in the search for organic molecule

formation clues. Rocks are obtained by drilling core samples as deep as

9.6 km from beneath the sea floor. In certain areas of the world sections

of core samples contain uninterrupted sequence of sediment from over

180 million years. These rocks contain skeletons of microscopic

plankton and clay–sized particles that can be used to piece together the

history of the Earth.

Deep submersible vessels have been used to obtain data and samples

from deep ocean trenches and under sea volcanic vents. These can be

22 Life on Earth

manned or robotic and controlled from a surface vessel, enabling a direct

view of the activity occurring in such hostile environments.

Scientific beliefs

Scientific ideas about the history of the Earth, the origin and the

evolution of life, must be based on evidence. The evidence must be

testable and available for all scientists to study. Scientific evidence and

scientific processes lead to a scientific view of the world. Technological

advances contribute to the scientific evidence available.

There are other ways to look at the world. For example, most people –

(including scientists) have a set of beliefs about ‘the meaning of life’ that

are not scientific. Such beliefs are a valuable part of culture.

You do not necessarily need to think that cultural ideas and scientific

ideas conflict each other. They are different ways to view information

and relationships. Each has its role. However, if you attempt to judge

scientific ideas using cultural beliefs, or judge cultural beliefs using

scientific evidence, you will often find conflict.

Throughout human history, there have been many cultural ways to

represent the origin and development of life. For example, here is a

presentation of a traditional Aboriginal Dreaming.

A dreaming perspective

The Aboriginal belief system is known as the Dreaming. In the

Dreaming, meaning is handed down from generation to generation by the

telling of mythological stories, which are often linked to the land.

The following stages give a brief outline of the formation of the Earth as

described in one version of the Dreaming.

A At the beginning the enormous flat mass of Earth was surrounded by

evil and murky water and everything was enveloped in darkness.

Sand and soil covered the surface and gigantic rocks were hidden

beneath the surface. These rocks were supported by many huge tree

trunks. Without this support the Earth would have collapsed in on

itself and be lost forever.

B Suddenly the Sun was born and he forced his way up through the

landmass and still water. This was thought to be the first man and

his face was a blaze of fire that shed light on the very flat and dusty

plains. The day ended when the Sun became weary and gradually

sank underground leaving everything in darkness.


C After resting, the Sun returned to the east through an underground

passage that he had made. The Sun felt he must once again see this

strange place. The Sun’s habits have been regular since this

first day.

D The Sun did not know that mysterious things were hidden

underground which only needed light to make them flourish.

The soil awakened and every day was different. Springs began to

trickle out of the dirt and these springs eventually formed creeks,

lagoons and lakes. Grasses, plants and trees rose from the soil

covered with fruit, berries and flowers. The Sun saw more and

different plants every day, while the trees grew in height.

E One day he saw an unbelievable change when the Earth beneath him

appeared to erupt. Level ground was pushed toward him as hills and

mountains appeared. Large trees and rocks rose from the soil and

flowing water was spread in all directions. The Sun saw that living

creatures were emerging from underground. They had been asleep,

but now they had light, water and plant growth, and it was time

to waken.

What is one conflict you observe if you judge this cultural perspective

using scientific evidence?

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

_________________________________________________________

Discuss with members of your community, family or class why it is

important to include a cultural perspective when considering the origin of

life on Earth.

_________________________________________________________

________________________________________________________

_________________________________________________________

_________________________________________________________

24 Life on Earth

Other cultural perspectives

Most ancient cultures have a version of the origin of life on Earth.

These are often referred to as myths, legends or cosmogonies.

Variations of these ancient creation stories are part of the beliefs of many

present day cultures.

You may be familiar with some of the various gods in the Greek myths

such as Gaia (Earth), Cyclops, the Titans, Aphrodite or Zeus in which the

history of the Earth’s creation is told as a story representing the Void

from which came the Earth. (You may wish to look up some Greek

myths by searching for Hellenic Cosmologies.) Hebrew creation is

represented in Genesis 1-3 in the Bible, in which God creates the Earth in

seven days. In Japanese creation mythology, heaven was formed out of a

limitless chaos from which three deities (gods) materialised, who were

ultimately responsible for life on Earth.

Using the reference on LMP website, look up some of the different cultural

explanations for the origin of life.

http://www.lmpc.edu.au/science

Complete Exercise 2.4: Science and belief systems.


Additional resources

Phanerozoic

Cenozoic

Eon Era Period Quaternary

Holocene

Tertiary

Mesozoic

Cretaceous

Jurassic

Triassic

Palaeozoic

Permian

Carboniferous

DevonianSilurian

Ordovician

Cambrian

Hadean

Archaean

Proterozoic

Epoch

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Palaeocene

Ediacaran

massextinction

oldest stromatolitesoldest evidence indicating life

age of BIFs

Mill

ions

of y

ears

bef

ore

pres

ent (

Ma

BP

)

012345

10

20

30

40

50

60

70

massextinction

100

200

300

400

500

600

Changeof scale

Changeof scale

1000

2000

3000

4000

Changeof scale

Precambria

(last 10 000years)

26 Life on Earth

Table for timeline

Date(years ago)

Event

1-2 million first humans

100 million first placental mammals

c.140 million first flowering plants

145 million first bird

c.200 million first mammals

320 million first reptiles

374 million first amphibians

420 million first vascular land plants

478 million first fishes-first vertebrates

540 million widespread appearance of animals with hard parts(eg. shells), including trilobites

c. 600 million first invertebrates (animals without backbones) with exoskeletons such asshells

670 million first multicellular animals eg. soft-bodied jellyfish

1.4 billion first eucaryotes (cells with a nucleus)

1.6 billion last banded iron formation

2.4 billion banded iron formations, last of the uraninites deposited

3.8 billion oldest known life form (stromatolite from Western Australia)Photosynthesis releases oxygen as a waste product

3.96 billion oldest known rock

4.6 billion formation of the Earth


Suggested answers

Types of fossils1 a) clam shells

b) a named fish

c) a named plant leaf

d) a snail

e) a type of crustacean

2 The organism died then was quickly buried before it started to

decompose. Eventually they became fossilised.

Formation of fossils1 Those organisms that are quickly covered by sediment have a greater

chance of fossilisation as decay may be avoided. Once the organism

is in its final resting place, buried and left long enough, sediments

covering it may form rock.

2 Trace or relic fossils are usually in the form of mineral-based

internal skeletons or external casings such as shells of soft-bodied

animals or as chemically resistant tissues such as wood or

leaf cuticle.

3 c, d, a, b

Heterotrophic procaryotic cells

With only heterotrophic organisms the amount of nutrients in existence

would be used up and life would die out. Heterotrophs are ‘other’

feeders, they cannot make their own food.

28 Life on Earth

Autotrophic procaryotes

The increasing amount of ozone enabled living things to move from

deeper water to the shallows and finally onto land as the ozone layer

increased.

Palaeonotological evidence1 Palaeontology is the study of past life in the form of fossils.

2 A study of palaeontology would provide evidence of the types and

abundance of organisms that existed in the past and possible changes

in their development that may have occurred over time.

Banded iron formations (B1F5)

The rock may provide evidence of increasing free oxygen in the

atmosphere.

Change from anoxic to oxic conditions

CO2 + H2O sunlight C6H12O6 + O2 + H2O

The amount of carbon dioxide would reduce and the amount of oxygen

would increase as a result of this process.


Exercises – Part 2

Exercises 2.1 to 2.4 Name: _________________________________

Exercise 2.1: Fossil evidence

Look at the photographs of fossils that follow.

Specimen A. (Photo: Monika Khun ©LMP.)

30 Life on Earth

Specimen B. (Photo: Monika Khun ©LMP.)

Select one fossil and answer the following questions.

Fossil selected _____________________________________________

1 What sort of present–day organism is this most similar to? Explain a

reason for your answer.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

2 Using the tables in the Additional resources, suggest the

approximate age of this fossil.

______________________________________________________

______________________________________________________

3 In what sort of environment would this organism have been found?

Explain your answer.

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________


4 Briefly describe how this fossil may have formed.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

5 Explain why there is more difficulty in obtaining fossils from ancient

rocks than those in rocks that are only a few hundred million

years old?

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

6 The fossil record indicates that some fossil species have disappeared.

Account for this disappearance of species in the fossil record.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

32 Life on Earth

Exercise 2.2: Evolution of life on Earth1 Identify the major stages in the evolution of life by filling in the

boxes below. The first one has been done for you.

organic molecules

2 When photosynthesis began it had long reaching effects on the

atmosphere changing it from an anoxic to an oxic atmosphere.

What significance did this event have on the evolution of

living things?

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________


Exercise 2.3: Evidence for the origin of life1 Outline an example of each of the following kinds of evidence that

suggests when life originated on Earth.

a) palaeontological evidence

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

b) geological evidence

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

2 Include the timeline that you drew for this Exercise.

Exercise 2.4: Science and belief systems1 a) Outline two changes in technology that have assisted scientists

to develop a scientific understanding of the origin of life and the

evolution of living things.

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

b) Why do scientists continually seek to improve technology to

gather and analyse information?

_________________________________________________

_________________________________________________

_________________________________________________

34 Life on Earth

2 a) Give an example of a conflict that occurs when a cultural

version of creation is judged using scientific ideas and

evidence? (You can use an example from Aboriginal Dreaming

story or from another cultural perspective).

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

b) Do you think that the scientific idea and/or evidence makes the

cultural perspective of the origin of life wrong? Why or why

not?

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

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