Learning with Granny!
A Journey through Time
This month Granny begins her Time trip. Let's listen as she and the
characters in her book learn about life on Earth following "The Big Bang'
(see earlier article) This month she
covers the bottom rung of her ladder (see
last month's article)- the
Paleozoic Era - and a little of the long time period that came before.
Pre-Cambrian Cambrian Ordovician Silurian Devonian Carboniferous Permian
 The Birth Of The Earth -
After they had cooled off in the sea,
everyone walked over to the rocky side of the shore. They enjoyed the rock-pools
and the boys were surprised how many different types of rocks there were. Some
were round and smooth, others were flat with layers of different colours, while
others looked like hardened bubbles with little holes all over. 'I think these
must have been thrown up when a volcano erupted' said Lee turning some pieces
over in his hand 'Was there a volcano here Granny?' asked Vinny. 'When the solid
crust of the Earth was forming, there were volcanoes all over and the surface
was changing all the time. The heavy material was settling into the Earth's core
and the lighter material was settling around the heavier material below.'
replied Granny. 'That would explain why some of the rocks have these neat layers
and the bubbly pieces could have been hot lava'
'I saw a movie once' said Terry
who had also become interested in the rocks 'it was about a volcano. The boiling
lava was pouring down the mountain-side, covering and killing everything in its
path - nothing was safe from its red, bubbling scalding hot liquid fire' 'I bet
that killed all the animals and birds and things living on the Earth Granny'
said Vinny. "No, this was all happening 4 billion years ago and there was
no life on Earth then' she went on 'but heavier basins were forming to accept
water to make oceans and lighter rocks were forming the land.'
'How did all the
different continents get their shape?' asked Terry 'Well at first there were no
separate continents - just one huge land mass called Panguea. The crust of this
huge land mass started to break up and after many millions of years to drift
apart.' Granny stopped as Ann had a question. 'How do you know that Granny?' Ann
had been sitting quietly with her feet in a rock pool. Granny had to think -
'One definite piece of evidence we have is that the same kind of rocks and
fossils have been found on continents that have separated like South America and
Africa. Do you know what fossils are? They are forms of life that have been
preserved as rock. Some of these life-forms are extinct or not living anymore,
and some look like their descendants that live on Earth today. Corals and sea
shells look very like fossil specimens'. 'Were they the first type of life on
Earth?' asked Lee 'One of the first' said Granny 'while the land mass was
forming it was being bent and buckled and pushing up mountains, it was cutting
river beds between the hills and across the country-side. Life began forming in
the sea. Tiny bacteria and algae....'
'Yugg! that's what's in our swimming pool
when we get back from holiday..' commented Vinny 'That's right , that's a very
simple life form, when it wants to reproduce, it simply breaks itself in two to
form another just like itself. This tiny life form did a very
important service to the world. They produced oxygen into the atmosphere to make
the air breathable. This enabled all living creatures and all plant life to
develop.' 'Was that 'the olden days' Granny' asked Ann. 'No' said Granny
laughing 'This period of time is called Pre-Cambrian or the Dawn of Life. It
lasted from 4 Billion years ago and ended 570 Million years ago or 4,000,000,000
to 570,000,000.'
Time Zones And Early Life On Earth
'The next period we will look at extends from 570 million years ago (MYA) to
225 MYA and is called The Paleozoic Age, or Age of coal, plants, fishes and
invertebrates ( animals with a backbone). Traces of life forms are very
primitive, sea creatures were more advanced. Some had left the sea to live on
land and evidence of their existence has been found in fossil form. The
Paleozoic Age is divided into six different groups, the first being Cambrian.
Do
you remember the first one we talked about?' 'Yes' said Vinny 'that was
Pre-Cambrian - like pre-school or pre-primary. I know why - because its comes
before Cambrian' 'Well done' said Granny 'this period lasted from 570 MYA to 500
MYA and in the 70 million years in-between, sea creatures in the sea, including
worms, sponges.....' 'Sponges?'..broke in Vinny 'Yes sponges' went on Granny
'are living sea creatures - don't you remember that lovely piece we found on the
beach?' 'Oh I wondered why you wanted it - sorry Gran - carry on' 'Trilobites -
little sea creatures rather like a crab that could throw off its shell as it
grew larger. It could roll itself up into a ball if danger threatened. It was a
scavenger and picked up scraps from the sea bed. Its body was flat and it had
eyes at the top. It had a pair of antenna and about 20 pairs of legs. There were
no plants yet, but some of the sea algae looked like sea plants. The land now
known as Gondwanaland showed signs of the continents starting to break away in
fact North and South America, Africa, Antarctica, Western Australia, India and
Southern Europe could all be seen'.
The next period was from 500 MYA to 430 MYA
and is called the Ordovician Period. During this 70 million years the weather
was warm and damp in the North and colder in the South. Sea animals were still
the main life and land life had started to appear. Plants and burrowing worms
were starting to live and the sea had animals with backbones. Primitive fish
with shells, coral life and clams began in this period too.' 'What were the
continents doing in this period Granny?' asked Terry 'They were all moving South
and were experiencing a lot of flooding' replied Granny just as a splash in the
pool sprayed them all with water. Vinny had dived in and everyone shouted at him
to 'stop splashing!'.... He popped his head out of the water and with a
mischievous grin on his face shouted 'Now you're having a lot of flooding'
Spiders and Scorpions On a Sunny Afternoon
'The next period is the third in the Paleozoic Era and is called the Silurian
Period' began Granny. 'It started 430 MYA and ended 395 MYA. Much of the land
was under flood water following the first Ice Age which covered the Earth with
ice and snow. A lot of the sand that had covered the land was washed off.
Scorpions and millipedes appeared from the water and primitive plants started to
live at the edge of the water. In the water coral reefs were being built and
fish appeared in the rivers.'
'The fourth period is called the Devonian Period
and it lasted from 395 MYA to 345 MYA. Spiders and insects appeared on land.
Fish with fins and scales and jaws lived in the sea and the first air breathing
vertebrate set the stage for the amphibians to develop, Does anyone know what an
amphibian is?' 'It can breath in and out of the water' answered Terry. 'Right'
said Granny and carried straight on 'The first forests began to grow in the lush
red soil that followed the flood' the next period 'The Carboniferous Period
followed. Most of the coal that has ever been used in the world was being formed
between 345 MYA and 280 MYA. The warm humid weather encouraged the growth of
huge trees and this is what has been compacted under the ground and has turned
to coal. Coal has been mined for many of hundreds of years and we still use coal
all over the world every day.'
'There must have been a lot of trees in those
days' commented Vinny. 'Yes' said Terry 'and remember there were no humans to
destroy them and cut them down'. 'The first reptiles began to appear developing
from the amphibians. The corals in the sea were growing in large numbers forming
huge reefs. There were still trilobites as well as many numbers of snails and
shell like creatures including cephalopods and nauticoids which inhabited the
ocean. There were now many types of insects and a giant dragonfly. There were
snakes and hard scaled fish and believe it or not... an old 'friend' had
appeared.....' Granny paused. 'Who?' asked Ann 'The cockroach' replied Granny
'yes the cockroach can trace his ancestors far further back than we can - right
back over 300 million years.'
'Please lets do the last period in the Paleozoic Era' begged Terry looking at
the chart. 'Right' said Granny 'The Permian is the last period in this group. It
lasted for 55 MY from 280 MYA to 225 MYA. The rocks are rich in deposits of
coal, oil and gas from the fossils. There was a lot of movement of the
continents and mountain ranges were formed. South America and Africa were
clustered down in the South with Antarctica, Australia and India -' 'India?'
said Lee 'what was India doing right down there, away from where it is now?'
'India met up with East Europe much later' answered Granny 'it crashed so hard
that it formed a ridge as it joined what is now the Himalayan Mountain range'
she continued 'At this time the sea life was very rich as the waters were
shallow and warm. However, towards the end of this period, there was a mass
extinction.'
'What's an 'extinction Granny?' asked Margie. 'I know' said Lee 'its
when all life is wiped out and there is not a single member of a species left'
'What about the cockroach?' Margie inquired. 'They didn't become extinct, but a
large group of corals, shellfish and invertebrates (creatures with a backbone)
did.' said Granny 'Amphibians were growing less in number - but reptiles were
undergoing big changes and mammal-like creatures were developing. Giant ferns
and pines appeared and insects, bugs and beetles were doing well and growing in
numbers.'
Granny stopped to look at Ann's puzzled face. 'Please explain what the
amphibians and the reptiles are, as well as what the mammal-like creatures are.'
Margie felt pleased to find out that it wasn't just that she was the smallest,
that she didn't understand some of the story , she listened carefully as Granny
explained to Ann. 'An Amphibian can live on land as well as in the water once
its grown up. It starts its life in water breathing with its gills and later
breathes with its lungs. Some amphibians we know today include frogs, toads,
newts and salamanders. They like nice wet places to lay their eggs. During the
Permian Period, there wasn't much water, so some amphibians developed into
heavily armored land living creatures. Reptiles are cold blooded scaly creatures
like snakes, lizards, crocodiles and turtles, who are all descendants of the
primitive reptile. The mammal-like reptile, that also came from the primitive
reptile, was the ancestor of all mammals. Mammals now are warm blooded with hair
or fur. The females feed their young on their own milk. Humans, dogs, rabbits
and whales are all mammals.
You will recognize the next picture from the one last month. This section
covers the period from the 'Big Bang to the Paleozoic Era.  See also some
of the interesting life forms that you might have seen if you were able to go
back over 500 million years ago. Just click on the picture on the right to see
the full image.
THIS MONTH'S POEM
Fossils
To learn more of what life was like before...
You need to look closely at the sea shore
At the muddy sediment down deep in the seas
Or in steamy swamps still dense with old trees
----------
The rocks and the mountains guard secrets too
Hiding fossils just waiting to tell more to you
Of many species who took part in a race
And left evidence of their life for you to trace.
-------
Some lost life’s race and have left no record
Others turned to stone so you can observe
So although the living things are long dead
We can learn of their past and go on ahead.
--------
J.L. Marais Dec 2001
Next month Granny will be chatting to you about the Mesozoic
Era.
Many of you will be more familiar with this period in time, as this is when the
dinosaurs were among the strange early creatures that walked the earth.
Granny looks
forward to letters from teachers and pupils and is happy to answer your
questions. Simply e-mail her at granny@scienceinafrica.co.za
Until Next Month...
Granny Jenny
|
