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Dinosaurs
3500 million yrs ago
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Archaeopteryx
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Charles Robert Darwin
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meat eaters
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The big BANG!
3500 million years ago

there are over four million different kinds of animals and plants in the world. Four million different solutions to the problem of staying alive. Together they form a bewildering and complex mosaic.

From fossils we know that the ancestry of many familiar creatures stretches back hundreds of millions of years. We also know that the oldest rocks contain fossils of only the most simple forms of life.

these are traces of algae that lived two thousand million years ago. they occur in flint-like rocks in Canada but elsewhere some ancient rocks contain microfossils that are well over three thousand million years old.

 

these immense periods of time baffle the imagination, but perhaps we can get some idea of the relative lengths of the various stages if we condense the whole history of life on earth into one year.

then, ten million years become one day. And on that calendar I'm talking in the very last moment of December 31st and primitive man will have appeared only a few hours ago in the early afternoon. the first back-boned animal will have crawled up onto land during the last week of November and these gunflint cherts will have been formed on June 15th.

Now let's go back way way to the beginning of January, to the beginning of life.

 

Over three and a half thousand million years ago our planet was radically different in almost every way from the one we live on today. Enormous volcanoes, much more widespread than today, built up mountains of lava and ash. the atmosphere was filled with gasses such as ammonia, methane, hydrogen and steam.

there was virtually no oxygen in the atmosphere. In consequence, there was no ozone layer and ultra- violet rays, in a strength that would be lethal to us, beat down onto the young planet.

Over millions of years the ultra-violet rays, together with heat and great electrical and radioactive discharges, produced a chemical soup in the muddy waters.

Complex carbon compounds appeared with extraordinary characteristics: they could make copes of themselves as well as cause the formation of proteins. From them developed the very first forms of life on earth.

Some of these bacteria-like organisms, like many which still survive today, produced oxygen as a waste product. they began to create the atmosphere we now breathe.

Some deposited lime as part of the chemistry of their body processes. Here in Western Australia similar bacteria still exist and build up strange pillars. This is as close as we may ever get to a scene of the world two thousand million years ago - mid-June on our imaginary calendar.

Outwardly things changed little for hundreds of millions of years.

Your own local pond can provide evidence of the next dramatic development. Around fourteen hundred million years ago (that's the middle of August on our calendar) some kinds of primitive cells began to collaborate to form complex cells. And some of them resembled the single cell organisms that still live in our ponds.

the amoeba seems to have animal characteristics.

....While these filaments appear to be simple plants.

Yet others seem to be half animal, half plant.

One of the most successful groups are the ciliates. they're covered with a coat of beating hairs - the cilia - which drives them through the water. the cilia also waft tiny particles of food into their gullets.

these ciliates are stalked and remain anchored to one spot, but others are large and mobile and actively hunt for food.

Just visible to the naked eye, these are close to the limits of size for single-cell life forms. But size can be achieved in a different way - by grouping cells together in an organised colony.

This hollow globe - called volvox - is composed of hundreds of cells, each with a tiny tail, but all beating in a co-ordinated way.

Inside the globe daughter colonies are formed.

there are many other types of colonial life-forms - including some five thousand species of sponge. None of them are fully co-ordinated multi-celled animals.

But this is: a little blob of jelly with just two layers of cells, a mouth, and a gut. It is one of the comb jellies - which swarm in the oceans but which are so transparent that they are hardly ever noticed. these are true animals with muscle fibres and a simple nervous system.

Medusae have similar characteristics but most of them have a surprising method of development. they begin their lives in a completely different form - like this. Each structure grew from a tiny free- swimming organism which settled on the bottom. Although it is truly animal, it developed like the branches of a tree bearing flower-like individuals called polyps. these filter food from the sea. Some kinds bud off and swim away as free medusae again.

Others produce medusae from special vessels.

these tiny creatures will eventually produce their own sexual cells for release and fertilisation in the sea. And then new colonies of polyps will appear. When sexual reproduction evolved, it greatly increased the potential for variation in offspring - and therefore the potential for new species. Around six to seven hundred million years ago (that's late October on our calendar) there was indeed a great increase in life forms in the sea; including jellyfish.

the larger medusae carry quantities of jelly in their umbrellas which makes them more robust in rough seas. Hence their popular name - jellyfish.

Some, with the aid of stinging tentacles, can catch and digest quite large prey. Others have elaborate ruffles for netting microscopic food.

This is not a single jellyfish but a colony; a colony of polyps that has gone to sea and assumed much the same outward shape as a single large jellyfish.

Another of these colonies is the Portuguese Man O'War. It has a bag filled with gas that supports the colony and sails it on the high seas.

Many colonial relatives of the jellyfish live in tropical seas, among them hundreds of species of coral.

In comparatively shallow waters many form gigantic skeletons of lime. the coral polyps produce these with the help of tiny algae in their tissues - extracting carbon dioxide from the water and releasing oxygen. At certain times of the year corals also release sexual cells into the water.

Some of the larvae that result begin new colonies. But in prehistoric seas such creatures may have been the starting point for new life forms. Suppose some didn't develop into corals but took to a creeping way of life - they might easily become something like this....

A juvenile flatworm.

Propelled by tiny cilia on its surface, this develops into an animals that has a definite front end and back end, is sensitive to light, and can move in a purposeful way.

there are many kinds of flatworm and they are very flat - and so able to absorb all the oxygen they need through their beautifully patterned skins.

A flat shape is not suited to burrowing in mud or sand. Nevertheless there is both food and safety at the bottom of the sea, and some worms changed from being flat to being round and long - a better shape for exploiting this habitat. Eventually worms developed protective shells over their backs and became molluscs. the first of them appeared five to six hundred million years ago (early November on our calendar). Some have a well developed head, with eyes and sensory tentacles, and a very efficient feeding organ - a long scraping tongue.

Molluscs with a pair of shells - bivalves - use their foot to pull themselves into the sand or mud where they can filter-feed unobtrusively.

Scallops are also filter feeding bivalves, but live on the sea bed.

Not only have they good eyes - they are surprisingly mobile.

the metre-long clam, on the other hand, is so huge that it cannot move around. It too is a filter feeder. Its fleshy mantle joins two shells forming a chamber through which it sucks water. And every so often it gives a conclusive shudder as it expels some waste.

A few molluscs have gone to the other extreme and become free-swimming. their shells have been reduced to mere scales within their bodies - or have been done away with completely.

Without a shell to protect them, these creatures defend themselves with a foul-tasting slime; and their brilliant colours may serve to warn off would-be predators.

these beautiful molluscs are called nudibranchs. they're more complex and larger then flatworms and need special breathing apparatus - the gills. In some species they are exposed like a bouquet.

Some have developed feathery outgrowths that enable them to float on the high seas. there - extraordinary as it may sound - they hunt for jellyfish.

In deeper waters swims a survivor of another successful group of molluscs which were very common in the seas of 500 million years ago - that's in November on our calendar - the nautilus. More common in the seas of today are their relatives, the squids. they have lost their shells - except for a horny, swords-shaped relic within their bodies which gives them some support. they use a kind of jet propulsion for fast swimming - but they can idle in any direction by waving the fin-like extension of their mantle.

Squids - and their close relatives the octopuses are the most active and intelligent of all the molluscs.

Living alongside many of these molluscs are members of another large group of marine creatures which probably had worm-like ancestors. they too appear in many forms, but they do have a five- armed radial symmetry in common.

Sea urchins are typical of this group. Amongst their spines you can see the characteristic tube-feet - which also help to manipulate food to the central mouth.

Close relatives, the starfish, have similar tube-feet - controlled by a hydraulic system that runs throughout the body.

they're slow-moving but they seem to have populated shallow waters almost everywhere; and the secret of their success lies partly in the mobility of their larvae. Too small to be noticed, these abound in the seas - a rich source of food for fish. Survivors are swept into every part of the oceans and then develop into the familiar adult forms. Most marine invertebrates go through this process - including molluscs. their larvae support the extra weight of developing shells with lobes covered by beating cilia.

This larva will not turn into a mollusc, however, but into a member of another large group of marine creatures that may have evolved from the same ancestors. It's a segmented worm. the segments, with their pairs of movable bristles, made sustained burrowing much easier.

But some relatives have put them to more sophisticated uses. these crustacean are built upon that segmented plan, but each part has become specialised - as antennae. Or food manipulators, or legs, or for breathing or for reproduction.

All these creatures have an external skeleton and it is clearly a very effective way of building a body - as these huge Japanese crabs show.

But the jointed skeleton has a very special quality - mechanically, it works just as well on land as it does in the water. So animals with such characteristics were able to move out on to land without much difficulty. And that's exactly what happened around 400 million years ago - about mid-November in our calendar.

Each spring, on the eastern seaboard of North America, a strange re-enactment of that momentous episode in life's history takes place. Horseshoe crabs have changed little for several hundred million years and are relics of the huge variety of segmented creatures that once swarmed in the seas and among whom were the first invaders of land.

they come on to the shore at night - but only to breed. At the centre of each mass is a large female and directly behind her, attached by his claws, a male who will fertilise her eggs. Other unsuccessful males crowd around.

the egg mass is laid several inches down in the sand and remains there while the tiny larvae develop inside. At the next high tide, about a month after the eggs were laid, the sea reaches them again.

the eggs rupture and the larvae swim free.

So the horseshoe crabs return to the sea; but long ago other segmented creatures successfully spent more and more time on land. From them evolved true land animals - including the ancestors of scorpions.

the land which, for so long, had been naked and sterile, had just begun to acquire patches of green Algae, and lowly forms such as mosses and liverworts, were now beginning to grow at the edge of water.

Into these miniature jungles came other invaders from the sea - again animals with segmented bodies but in this case the ancestors of millipedes. they were vegetarians an the biggest today are only a few inches long; but many of the ancient forms that pioneered life on land grew much larger. One, indeed, was as long as a cow.

Spiders also evolved from ancestors like those of scorpions. Early in their history, they developed glands in the abdomen with which they produce silk. they use it in hunting, sometimes laying long trip lines sometimes intricate webs. they manipulate the threads with modified limbs, the spinnerets.

Any small creature trying to make its way here will blunder into the silken trap and while it is still entangled, the spider will pounce.

Reproduction, for all these land creatures, presented new problems. Without water to transport sperm to egg (as there was in the sea) - male and female had to get together. For hunters this is a complicated and potentially dangerous process. Individuals must make sure that their prospective partner sees them as a mate rather than a meal. And so, as these spiders demonstrate, elaborate signalling rituals were developed.

As the male approaches, he abandons his visual signals and adopts tactile ones. He has prepared for this encounter by taking up some sperm, dropped from his abdomen, in two special feelers, the palps. Now he must reach over the female, so that he can pump sperm from one palp into one of the female's sexual pouches - it's rather like liquid being squeezed out of an eye dropper.

About four hundred million years ago, new creatures appeared which were to be forerunners of probably the most successful group of all animals without backbones - the insects. they were not unlike the silverfish which still survive today.

they feed on vegetable matter, but as plants grew taller, and food became more inaccessible, they had to do more climbing. And getting down again might sometimes have been worse than getting up. Maybe that was one reason for a dramatic development. Some little creatures developed wings for flying from plant to plant.

Wings probably evolved from tiny lobes on the back. Today dragonflies develop their wings in just this way, repeating millions of years of evolution in just one night.

the wings are stretched taut by blood pumping into the veins.

Later the blood is drawn back into the body and the gauzy wings slowly dry and harden.

Insects were the first creatures to take to the air - over 380 million years ago, and they were to have it to themselves for 100 million years.

Dragonflies, among the first fliers, are superb aeronauts, and can reach speed of 20 miles - 30 kilometres - an hour. Damselflies are their smaller relatives. the wings of these insects beat so rapidly that only a slow-motion camera can show how they fly. the action is here slowed down one hundred and twenty times. the insect gets lift on the downbeat of the wing by twisting it so that the leading edge is inclined downwards. But at the bottom of the stroke the wing is twisted back, so that it obtains lift on the upstroke as well. It's an intricate set of mechanical movements which man has never matched in the air.

By the time the first insects were flying, the plant life on earth had undergone dramatic changes. By developing new types of cell, plants had solved the problems of desiccation and support out of water; and they had flourished and grown tall.

But they still needed water to transport their sex cells from one individual to another - and that meant that they could still only grow in damp places. But eventually that problem too was solved - and conifers were among the first to do so - by developing pollen and using the wind.

It is a haphazard method of fertilisation so pollen has to be produced in huge quantities. One cone may produce several million grains and there are thousands of cones on an average sized tree. the female cones are fewer in number. they grow on the same branches as the males but are in conspicuous positions on the tips of shoots.

Pollen, falling upon the female cone, is only the start of a very long process. For two years the cone grows, developing wrappings around the fertilised eggs. they eventually dry out and release small neatly-packaged objects. Seeds - the first plant eggs to have been fertilised without the help of water.

Today about one third of our forests are formed by conifers. And the biggest living organism of any kind is one - the giant sequoia of California - 120 metres, 380 feet tall.

Conifers have a special way of healing wounds to their trunks - they seal them with resin. When it first flows it's runny, but it soon forms a sticky lump which not only covers the wound but incidentally acts as an insect trap.

Lumps of resin from the ancient coniferous forests survive as amber and in them are insects - as perfect now as the day when they blundered into the resin a hundred million years ago. From fossils like these we know that the insects at that time had developed into an enormous variety of forms, swarming through the trees and plants and feeding on pollen, leaves, and wood - just as they do today.

Bugs stab stems will stiletto-like mouthparts to reach the sap.

Over 3,000 species of aphids alone tap this ready source of food in plants, all over the world. All they do is pierce the plant vessels - and the pressure of sap does the rest.

Grasshoppers chew vegetation. there are over 17,000 members in their group alone. Well over a million species of insects have so far been described and labelled.

Each species may swarm in unbelievable numbers. these are locusts.

there may be as many as a million million individuals in a single swarm.

Each group of insects developed their flying skills in different ways. the lacewing, for example, has two pairs of wings - just as the dragonflies and their relatives have. Its flight is here slowed down over a hundred times. This basic design was modified by other insects.

Not requiring any great speed for catching prey, the caddis fly overlaps its two pairs of wings to produce a broader unified surface.

But bees must have compact wings which can be neatly folded for social encounters in the nest - or when visiting food sources. To achieve enough lift, their smaller wings must beat faster.

It appears as if they have only one pair of wings, but they also have two - hitched together to form a single surface by a line of hooks along the front edge of the back wing.

Beetles spend a lot of their time in dense vegetation and litter - and they have converted their first pair of wings into protective covers.

Spring-loaded joints in the veins of the wings are used to fold them away when not in use.

Once in the air, the protective wing covers are held up out of the way. Beetles are the least agile of insects in flight. the most skilled are surely the flies.

Flies seem to have lost the rear pair of wings, but we can discover what has happened to them by looking at one of their relatives - the crane fly, or Daddy longlegs. Those two objects like drumsticks swinging up and down are the remains of the back pair of wings after millions of years of evolution. they beat very fast (they're slowed down 120 times here) and by acting like gyroscopes they enable the fly to be aware of the attitude of its body in the air, and to detect changes in its flight path.

Plants now began to exploit this achievement of the insects in the air. they did so by evolving flowers - and colour came to the world as never before.

Flowers carry both male and female sex organs and they first appeared about 100 million years ago - about December 20th on our calendar.

their colours and scent are designed to attract insects, the nectar to reward them. the insects unwittingly carry pollen from the male part of one flower to the female parts of another, and plants have evolved an infinite variety of ways to increase the efficiency of this transport system.

Colourful patterns.

Lines to guide the insect into the flower;

And some patterns, in the ultra-violet part of the spectrum, that can only normally be seen by insects.

the structure of flowers has also evolved to suit certain kinds of insects. Salvia only opens its doors to the weight and shape of a bee as it lands on the flower's flight deck. This triggers the stamens to stamp pollen on the top of the bee's abdomen.

the flowers go on producing nectar for a few days and then their ovaries become mature. At this stage, when a bee visits, it's another part of the flower, the stigma, that jerks down to collect the pollen brought from another.

Such relationships have led to many complicated pollinating mechanisms - such as those of the orchids. This one gives off a perfume like that of a female ichneumon wasp. When a male arrives, he finds something that not only smells like a female, but looks remarkably like one. At one end of the bloom there's a mass of pollen shaped like a horseshoe.

the ichneumon male copulates with the flower.

And the pollen mass is so placed and shaped that it fastens neatly onto his abdomen.

This orchid is totally dependent on this one species of ichneumon wasp for pollination - and therefore reproduction. As a species, the orchid can only survive as long as there are ichneumon wasps to pollinate it.

the seductive odours and beguiling shapes of flowers are so attractive to the insects for whom they were evolved that they are virtually irresistible. And other insects turn that to their advantage in a different way.

the ginger flower has petals that move.

It's one of the most extravagant designs of any insect, for this, with flaps on its legs that perfectly match the petals of the flower, is a mantis.

the butterfly comes to sip nectar.

the flesh of an insect is succulent but the mantis has first to deal with the external skeleton, made of chitin. Chitin won't expand, so, in order to grow, all insects must periodically shed their skin. This spiny leaf insect has just begun that process.

the old shell hangs from the branch above it, like the ghost of its former self.

Some insects have simplified the problems of growth by leading split lives, and at the same time exploiting different food sources. This little creature will eventually become a butterfly but, for a while, it will keep its body as simple as possible - as a caterpillar. Caterpillars are little more than eating machines. they won't breed, so they don't need sexual organs and wings. Hatched on their own food plant, all they need is an efficient pair of jaws and a bag-like expandable body.

Because they are soft and vulnerable caterpillars need all the protection they can get; some have markings like a fearsome eye;

Many are extravagantly decorated and coloured - a declaration to would-be predators that they are unpalatable.

Long hairs can sometimes be tipped with poison - enough to cause a rash on human skin.

When they've grown as much as they need caterpillars prepare for the first of two highly dramatic transformations. Moths' caterpillars make this change in private, first spinning a silken shroud.

Within this cocoon the caterpillar's body breaks down into a kind of soup. Clusters of dormant cells will become active, multiplying and reassembling a new body - a new form.

Butterfly caterpillars embark on the same change unscreened by a cocoon but usually in an inconspicuous position close to a leaf or stem. Here the old skin has split and the chrysalis has emerged, inside which the final transformation will take place. After a few hours the skin hardens, and, in this case, becomes opaque and almost metallic.

the body of a butterfly may take several months to rebuild - or as little as a week.

the wings are crumpled bags, but the insect pumps blood into them and they slowly expand.

they dry and harden - until at last the butterfly is ready for flight.

the time for growth is over - the primary task now of all these butterflies is to find a mate.

Bird-wing butterflies of the Far East are among the largest in the world.

And the atlas moth is one of the largest moths. Its body is small, though, compared with the average bird, but it is close to the limit of size for the insect design.

Yet insects have found a way of transcending that limitation in size.

Numbers! This is a colony of army ants. Such a colony may consists of 150 to 170 thousand individuals, yet they act as one super-organism. Here they have made a bivouac in a hollow tree. Inside a living shelter of workers and defending soldiers, the queen will lay between 100 and 300 thousand eggs. For three weeks her enormous family will be carefully tended, until the colony is ready for its nomadic phase - ready to go to war.

Now they will kill every living creature in their path that cannot run from them.

This super-organism can only be compared to a beast of prey - as powerful and long-lived as many of the hunters of the jungle.

In the same tropical forests are more gentle colonies of insects. these parasol ants are equivalent to a large browsing animal rather than a beast of prey. the workers strip trees of their leaves, cutting them into tiny pieces and then transporting them to their vast underground nest. the work goes on day and night. the ants will not eat the leaves, for they can't digest cellulose. Instead they chew them up and make a kind of compost. And on that they cultivate a fungus in their underground galleries. And that they do eat.

Not far from the nest the ants have their refuse tips.

Every now and again the workers turn their attention to cleaning out the nest. the fungus which the parasol ants grow can survive nowhere else. Plant and insect are utterly dependent on one another.

the ancestors of the insects emerged on to land about 400 million years ago. But by then different forms of life, with bodies built on a radically different plan had emerged in the seas, and it's they that we'll be looking at in the next programme.

 

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