Timeline Teachers Page Version 3b

8/13/2019 Timeline Teachers Page Version 3b

1/5

Teachers notes

Geological timeFor many, the concept of time is difficult to grasp. Yet even in Key Stages 1 and 2, children areexpected to understand long periods of time: the activities of the Egyptians 4000 years ago, the Romans2000 years ago or the Vikings 1000 years ago. If one thousand years is a long time, how can a child

comprehend one thousand million years? But not only is it possible, it is intellectually stimulating.Geological time means large numbers and it is necessary to break down these vast periods of time intomore manageable pieces. Scaling is a useful tool.

There are a number of models that have been used to scale the passing of the 4600 million years ofthe Earths geological history. Compressing geological time into, for example, a 460-page book, thetwenty four hours of the day or even to a single hour have been used. These are misleading, however,as they gives the impression that, with the appearance of humans a few seconds before mid-night,geological time came to an end and that our species is the ultimate life form at the end of the longevolutionary process. This is far from the truth. If survival of the fittest is the key to evolution, wehave a lot to learn from blue-green cyanobacteria!

The Geological Timeline

It has been estimated that the solar system is about half way through its life, so the model presentedhere scales geological time to that of a middle -aged person. We consider the Earth not as a planet 4600million years old, but as a person 46 years old today. Of course to an eight or 12 year old child, it isdifficult to imagine that anybody could be as old as 46, but discussion about the age of relatives(parents and grandparents and teachers?) makes this more understandable. For a child, the samemental agility is necessary to come to terms with 46 years, as for 460 years (the Tudor period), 4600years (Egyptians were about to construct the pyramids) and 4600 million years (the age of the Earth).

The Geological Timeline introduces the question what of the future? Our middle-aged Earth is partway through its life. It is interesting to debate what the worlds environment might be in anothermillion or 4000 million years. Will humans still exist? What will be the effect of humans on

biodiversity? What organisms might evolve? What might the atmosphere be composed of? How will itall end?

Classroom activitiesA timeline is the ideal way to comprehend the passage of geological time and to demonstrate how life,environment and geography has changed throughout Earths history. There are several ways that thiscan be achieved in school. A piece of wall - paper 4.6 metres long could be stretched around a room, divided up into forty -six

rectangles. A 4.6 m length of rope, like a washing line, can be stretched across a playground with a peg every

10 cm . An interesting project is to draw the timeline by computer.

Whatever method is appropriate, subdivision into 46 units is useful as these give the idea of the 46birthdays (each birthday represents 100 million years of geological time). It is helpful if the lastdivision (representing the last year) is an elongate rectangle divided into 12 months a lot happenedduring that last year. The childrens work can be attached to the timelinewritten work, photographsor art work.

The key geological events in the history of life are shown in the Geological Timeline and further detailsare shown in the table below. It should be noted that some of these events did not fall exactly on theEarth's 'birthdays', but they have been placed next to the nearest one. So the appearance of thedinosaurs 225 million years ago, for example, has been placed at the 44 th birthday (so within 25 millionyears). Of course absolute ages are approximate anyway and the degree of error and uncertaintyincreases with age. Taking the Carboniferous as an example, its lower boundary been variously dated

between 367 and 353 million years ago and the top between 280 and 301, and is, therefore, between 52and 87 million years in duration.

Cross-curricular activities:These will depend on the age and ability of the children:


2/5

Mathematics measuring (along a timeline), scales, calculations involving time. English written work on a period of time, organisms, rocks, etc. Science what is life; relationship between organisms and the environment they live in; changes

in the environment; Earth studies Art depiction of life in the past IT construct a time line on a PC. Students artwork can be scanned and attached to their time

line (or digitally based artwork packages can be used). Pictures of fossils, rocks, minerals, maps,etc, perhaps taken from the Web or from clip-art packages can be used. Hyperlinks can be used tolink the time line to additional information (e.g. students' written work or art work).

Theology this is a difficult subject, but here we present the scientific view of geological time andthe evolution of life. How does this compare with religious beliefs?

Further readingA number of scientific palaeontology books are available, providing data that can be used on atimeline. The majority are for advanced students, but a brief outline of the fossil record, including ashort reference list, is published by the British Geological Survey:Rigby, S. 1997. Fossils, the story of life. 64pp [British Geological Survey, Keyworth]

The Fossil Focus series is also published by the British Geological Survey. These laminated A3 cardscolourfully explain the anatomy, distribution and environmental requirements of a number of fossilgroups. A list can be found in the BGS catalogue and by visiting its web site (www.bgs.ac.uk).


3/5

TheTimeline inb irthdays

Approximateage of the

Earth(millions of

years)

Approximatetime before

present(millions of

years)

Notes on key events along the Timeline

0 0 4600Earth formed from a dust cloud with the sun in centre. When Earth was about80% of its present size, it crashed with another planetoid, debris around theEarth which fused together to form the moon.

1 100 4500Earth's core formed when dense metals sank to the centre. Eventually the stonycrust cooled and solidified. Little is known about Earth (no crustal rockssurvive).

2 200 4400Oldest known minerals to form on Earth are zircon crystals in Australia.Inclusions said to indicate oceans had formed by this time, although this iscontroversial.

5 500 4100 End of the Hadean (the name of the essentially unknown phase of Earthshistory, not represented by crustal rocks).

6 600 4000 The Ancaster Gneiss (Greenland) are Earths oldest known crustal rocks (c.

4000 Ma).8 800 3800 Akilia Gneiss (3850 Ma) said to have carbon traces of life, but this iscontroversial.

9 900 3700

Banded Ironstone Formations (BIFs) are considered to have been created by bacteria. Oxygen created by bacteria caused ferrous iron in the ocean water tooxidise and precipitate as a red layer of iron on the sea floor. At times whenoxygen was not being created, grey cherts were precipitated instead. Theselayers built up alternately to form BIFs. BIFs provide the earliest signs of

photosynthesis. They began to form about 3700 Ma, but no fossils are known.However, photosynthesising bacteria must have evolved from non-

photosynthesising ancestors, which in turn evolved via non-biologicalevolution.

11 1100 3500

The Apex Chert (western Australia), 3465 Ma old, was once believed to contain

the earliest fossils, but this is now considered unlikely. However, in the Pilbararegion, NW Australia, silica-rich rocks dating to about 3500 Ma contain tubesabout 40 microns long and thinner than a human hair. Although some may haveformed inorganically, there are some geologists who believe that they wereformed by rock-eating bacteria. This is still controvercial.

16 1600 3000

Stromatolites formed by blue-green cyanobacteria, microscopic, single celled, photosynthesising organisms. They formed a mat of calcite removed from thesea water, which gradually built up to form domes. Blue-green bacteria are stillmaking stromatolitic domes in Shark Bay (Australia) 3000 million years later.

25 2500 2100

Oxygen was a waste product produced by bacteria and would have been poisonous to these early life forms. Initially the oxygen was trapped in therocks, e.g. BIFs and limestones, but eventually there was too much to store inthis way and it escaped into the atmosphere. Terrestrial Red Beds werecreated 2100 Ma, by the oxidisation of iron. Eventually free oxygen began toaccumulate in the atmoshphere.

31 3100 1500

Small amounts of oxygen in the atmosphere. The first eukaryotes appear, the basic cell type that almost every living thing on Earth is made ofprotista,fungus, plant, animal kingdoms (only bacteria , Kingdom Monera , have thesimpler prokaryotic cell). Eukaryotes require oxygen for their metabolism.Sexual reproduction is said to have evolved at about this time. Rocks 1000 Maold show an increase in diversity of these early eukaryotes, protista.

39 3900 700

Geneticists have suggested animal life began c. 1000 Ma ago, but there is noevidence for this in the geological record. Choanoflagellates are protistids withgenetic material also found in animals and it has been suggested that the animalkingdom evolved from something similar. The earliest trace fossils in Australiaand Africa are about 700 Ma old.

40 4000 600 The first multicelled animal fossils including the sea-pen Charnia , worms, seaurchin-like creatures and jelly fish, are a little over 600 Ma old. Fecal pellets


4/5

discovered in 600 million year old rocks in Scotland must have been left by ananimal with a gut.

41 4100 500

Animals with hard parts (shells and skeletons) e.g. trilobites and molluscsevolved 545 million years ago (at the base of the Cambrian). Soon afterwards,all kinds of organisms with hard parts began to evolve, including corals,crinoids, brachiopods, nautiloids, graptolites and microscopic species too (e.g.foraminifera). The earliest fish evolved in the early Cambrian. The first fishwith calcareous back bones (rather than cartilaginous notocords) evolved a littlelater. Comparison can be made to other vertebrates including ourselves.

42 4200 400

Sufficient ozone in the atmosphere allowed plants to evolve from algae andcolonise the land. Invasion of land by plants began with the evolution of non-vascular bryophytes in the Mid Ordovician, about 450 Ma ago. Cooksonia, thefirst vascular plant, evolved in the late Silurian, c. 420 Ma ago. Soon afterwardsanimals followed the plants.

43 4300 300

Animal life has been found on the marshy land associated with early plantfossils. Worms, snails and, by the late Devonian (about 350 Ma), the firstamphibians (tetrapods) left the aquatic realm. Amphibians rapidly evolved intolizards. Lizards had developed a water proof egg that did not have to be laid inwater. They did not have a need to stay close to bodies of water and keep wet.The first tropical rain forests evolved (the coal forests) and began to spreadabout 320 Ma ago.

44 4400 200

Lizards evolved into dinosaurs 225 Ma ago.There are a number of differences, but the most obvious is in the construction of the hip so that dinosaurs were ableto stand with straight legs beneath their body. Some were bipedal. 'Mammal-like reptiles' evolved into the first mammalsshrew-like insectivores about210 Ma ago.

45 4500 100

Archaeopteryx , the first bird, evolved from feathered theropod dinosaurs about140 Ma ago. Soon afterwards (c.130 Ma ago) flowering plants evolved

Archaefructus was the earliest angiosperm (it had carpels but no flower), butsoon afterwards species related to magnolia appeared (oldest fossil flower).

8 monthsago 4535 65

Mass extinction of 65 to 70% of all species, including all the ammonites,

belemnites, flying reptiles and dinosaurs (although birds, the last of theevolutionary line of the dinosaurs continued to thrive).

7 monthsago 4550 50 60

After extinction of the dinosaurs, very rapid mammalian evolutionary radiation,especially in the Eocene (about 40 55 million years Ma), occupying land, seaand air.

4 monthsago 4565 35Ma

The first primates, related to lemurs, evolved late in the Cretaceous, just beforethe mass extinction and the disappearance of dinosaurs, ammonites etc.Monkeys evolved about 35 Ma ago and started to evolve rapidly: thedryopithecines appeared about 25 Ma and the first apes 17 Ma. .

2 monthsago 4585 15

Grass evolved. This is, perhaps, the most important flowering plant so far ashumans are concerned as it provides us with wheat, barley, maize, rice, etc. Thefirst grasslands evolved during a prolonged phase cooling climate. A number ofanimals took advantage of the expanding grasslands, including some of the

primates that live on the ground rather than the trees.

About 3weeks ago c. 5-6

The hominid Australopithecus evolved (hominid and human should not beconfused; Australopithecus was not human). There have been several species.Recently a skull c. 7 Ma old was discovered that has been suggested to be theearliest hominid but some believe it to be the skull of an ape. Australopithecusafarensis ('Lucy') evolved about 5 Ma ago and the last species of

Australopithecus boisei ('Nutcracker Man'), lived from 2.3 to 1.4 Ma ago.About 7 8days ago 2 2.5

The first species of human evolve in Africa Homo habilis . Fossils of their brain case shows that the speech centre is only just beginning to develop.

c. 6 7 daysago

Almost4600

2 1.6 Homo erectus is considered by some to be two species- H. ergaster and H.erectus . They evolved in Africa about 1.6 Ma ago. Homo erectus was the firsthuman species to migrate across Europe and Asia.


5/5

c. 5 daysago until

'last night'1.3

Ice ages start, but this was a period of very variable climateBritain wassometimes buried beneath about 1 km thick ice caps, sometimes tundradeveloped, sometimes it was warmer than today. During warm periods, lionshippo and rhino lived in Britain, but when the tundra developed, mammoth,wolves and giant elk lived here. The last glaciation in Britain ended about10 000 years ago.

c. 2 daysago 0.5

Homo heidelbergensis evolved. The earliest fossils are c. 500 000 years old.'Heidelberg Man' is also known as 'Swanscombe Man' and 'Boxgrove Man' inBritain.

TheTimeline inb irthdays

Approximateage of the

Earth(millions of

years)

Approximatetime before

presentNotes on key events along the Timeline

c.13hoursago

150 000 yearsago

Homo neanderthalensis evolved and spread throughout Europe during the 'IceAges' - fossils are found particularly in Mediterranean countries, but alsoGermany (the type area) and they also reached Britain. It possibly evolved from

Homo heidelbergensis. c. 12hoursago

130 000 yearsago

Modern humans ( Homo sapiens ) evolved in Africa about 130 000 years ago, perhaps from 'Rhodesia Man', Homo rhodesiensis , but the evolution of Homo iscontrovercial and there are a number of different evolutionary theories. Theidea that we evolved from Homo neanderthalensis is flawed.

c.3.5hoursago

c. 35 000 yearsago

Humans left Africa c.35 000 years ago to spread over Europe and Asia. Neanderthals became extinct about 30 000years ago.

c.1hourago

c.11 000 yearsago

Man became a farmer.

4 6

c.1minute

ago

4600

250 years agoThe Industrial Revolution. During the last 60 seconds we have pollution,radioactive waste, hole in ozone later, acid rain, mass extinction, etc.

The future 4600-9000 The next 4 600million years

What next? The world has changed so much in the last 4600 million years whoknows what will happen in the next.In the short term- More pollution? More extinctions? Changes in theatmosphere? Global warming? Rising sea levels and flooding of the continentalmargins?In the medium termthe extinction of human beings. What will evolve todominate the world then? The mammals had to wait for the extinction of thedinosaurs before their sudden evolutionary radiation. What is waiting for ourextinction? Could it be the turn of the insects? Or something totally unknown?In the longer termreorganisation of the continents. Greenhouse and IcehouseEarth? And finally the sun becomes a red giant, destroys the planets and dies.

Documents

Timeline Teachers Page Version 3b