0:00:49 > 0:00:53There are some four million kinds of animals and plants.
0:00:53 > 0:00:58Four million different solutions to the problems of staying alive.
0:00:58 > 0:01:03This is the story of how a few of them came to be as they are.
0:01:46 > 0:01:52The South American rainforest - the richest assemblage of life in the world.
0:01:52 > 0:01:59Those are Howler monkeys there are 50 kinds of monkeys in these forests.
0:01:59 > 0:02:07Some of the most beautiful creatures here are hummingbirds - 54 kinds were found a few miles from here.
0:02:07 > 0:02:11And over 300 have been found in South America.
0:02:11 > 0:02:18Nobody knows how many kinds of animal there are here - wherever you look, there's life.
0:02:31 > 0:02:36There are several 100,000 different insects that have been named,
0:02:36 > 0:02:40and, no doubt, hundreds more that haven't.
0:02:40 > 0:02:44All these varied creatures and plants form one complex mosaic.
0:02:51 > 0:02:55The orchid needs the bee to pollinate it.
0:02:55 > 0:03:00The anteater couldn't have existed before the ants.
0:03:00 > 0:03:05So unless the whole complex came into being in one flash of creation,
0:03:05 > 0:03:10different organisms must have appeared at different times.
0:03:10 > 0:03:13Which came first? And why such variety?
0:03:13 > 0:03:21Such questions obsessed a 24-year-old Englishman who came to these forests in 1832.
0:03:21 > 0:03:29He was Charles Darwin and he was enthralled - ecstatic - by the richness of life he found.
0:03:29 > 0:03:37In one day, in a small area, he discovered 69 different species of beetle.
0:03:38 > 0:03:40As he wrote in his journal,
0:03:40 > 0:03:44"It's enough to disturb an entomologist's mind,
0:03:44 > 0:03:49"to contemplate the future dimension of a complete catalogue."
0:03:49 > 0:03:56The conventional view of the time was that each and every species of animal and plant
0:03:56 > 0:04:00had been individually created by God.
0:04:00 > 0:04:02And Darwin was no atheist.
0:04:06 > 0:04:10For three years, the Beagle sailed around South America
0:04:10 > 0:04:13and up into the Pacific.
0:04:14 > 0:04:17600 miles west of Ecuador,
0:04:17 > 0:04:21they came to the lonely Galapagos Islands.
0:04:40 > 0:04:45It was here that Darwin's doubts about the Creation re-awakened.
0:05:00 > 0:05:06Everywhere Darwin found creatures resembling those on the mainland.
0:05:09 > 0:05:13But nearly all were slightly different.
0:05:13 > 0:05:17These were, without doubt, cormorants -
0:05:17 > 0:05:22like those he'd seen flying along Brazilian rivers.
0:05:22 > 0:05:26But here, their wings were so small and with such stunted feathers,
0:05:26 > 0:05:31that the birds had lost their power of flight.
0:05:32 > 0:05:35And these were clearly iguanas.
0:05:35 > 0:05:38He'd seen them climbing trees and eating leaves.
0:05:38 > 0:05:44But here on the Galapagos, where there was little vegetation,
0:05:44 > 0:05:50iguanas fed on seaweed. And they were not the same - smaller, darker,
0:05:50 > 0:05:56with long claws to keep a foothold in the crashing breakers.
0:06:02 > 0:06:05They also had extraordinary habits -
0:06:05 > 0:06:10swimming fearlessly out to sea and diving deep to graze on the seabed.
0:06:23 > 0:06:31The Galapagos Islands got the name from the tortoises that lived here which sailors slaughtered for food.
0:06:31 > 0:06:37These too, were obviously different from mainland tortoises.
0:06:37 > 0:06:40They were many, many times bigger.
0:06:40 > 0:06:48The Vice-Governor of the Islands told Darwin he could tell where a tortoise came from by its shape.
0:06:52 > 0:07:00This, with a deep rounded shell is from a well-watered island and feeds from vegetation on the ground.
0:07:05 > 0:07:11This has a peak to the front of its shell, so it can stretch its long neck upwards.
0:07:11 > 0:07:17It comes from an arid island where they have to crane up to reach the food available.
0:07:20 > 0:07:24His suspicion grew that species weren't fixed for ever.
0:07:24 > 0:07:31Perhaps they came from common ancestors and had changed to suit their particular islands.
0:07:35 > 0:07:42The differences that Darwin had noticed among these animals were all tiny.
0:07:42 > 0:07:47But if they could develop, wasn't it possible over millions of years,
0:07:47 > 0:07:53a series of such differences might add up to one revolutionary change?
0:07:53 > 0:08:00Wasn't it possible that amphibians had developed water-tight skins and turned into reptiles?
0:08:00 > 0:08:06Or that a reptile had developed feathery scales and become a bird?
0:08:06 > 0:08:12Or that man himself might be descended from a group of tree-swinging apes?
0:08:13 > 0:08:21The idea wasn't new - others had suggested that all life might have a common ancestry.
0:08:21 > 0:08:27But Darwin went further and gave the idea more force by suggesting a mechanism
0:08:26 > 0:08:32which might have brought it about - he called it "natural selection".
0:08:34 > 0:08:37Put briefly, his argument was this,
0:08:37 > 0:08:41individuals of some species aren't identical -
0:08:41 > 0:08:47some tortoises have slightly longer necks than others.
0:08:47 > 0:08:52In times of drought, they could reach leaves - and live,
0:08:52 > 0:08:55while the shorter-necked ones die.
0:08:56 > 0:09:02So those best fitted will transmit characteristics to their offspring.
0:09:04 > 0:09:07Eventually, tortoises on arid islands will have longer necks.
0:09:09 > 0:09:14So, one species will have given rise to another.
0:09:18 > 0:09:26In these programmes, we'll survey the great variety produced by natural selection
0:09:26 > 0:09:32and look at them, not as oddities, but as elements in the long story
0:09:32 > 0:09:37that began 1,000 million years ago and is still continuing today.
0:09:37 > 0:09:40Some creatures, mammals like these sealions,
0:09:40 > 0:09:45and myself - mammals both - are recent arrivals on the scene.
0:09:45 > 0:09:53Others - birds, reptiles, amphibians, fish - have been here long, longer than we have.
0:09:53 > 0:09:59In places where conditions have remained unchanged over immense periods,
0:09:59 > 0:10:06there are creatures resembling closely their ancestors - they can tell us a lot.
0:10:06 > 0:10:12But to disentangle the story, we'll also have to look for evidence in the rocks.
0:10:20 > 0:10:26Bodies fall to the bottom of seas and swamps and get entombed.
0:10:28 > 0:10:36The sediment, after millions of years, turns to rock and these remains survive as fossils.
0:11:00 > 0:11:05Since discovering radioactivity, scientists have developed ways of measuring the age of rocks.
0:11:13 > 0:11:19There are simpler ways of establishing the age of rocks that anyone can use.
0:11:20 > 0:11:26There's no more dramatic place to do so than the Grand Canyon in the American West.
0:11:39 > 0:11:46The Colorado River, aided by wind and rain, has cut a section through the sandstone and limestone.
0:11:48 > 0:11:55The layers lie undisturbed so obviously the lower ones were deposited before the upper ones.
0:11:55 > 0:12:00So if we want to trace the ancestory of life back to its beginnings,
0:12:00 > 0:12:02we must go deeper into the canyon.
0:12:16 > 0:12:24This is the greatest gash in the earth - from rim to bottom is a vertical mile.
0:12:24 > 0:12:30There are many trails down and the usual way is on the back of a mule.
0:13:12 > 0:13:20Here we're 500 feet from the lip of the canyon and the rocks are 200 million years old.
0:13:20 > 0:13:28There are no mammal fossils but there are four-legged animals - small reptiles.
0:13:28 > 0:13:36A lizard-like creature that left tracks here which was once the face of a sand-dune.
0:13:50 > 0:13:59Farther down, no reptiles, but in limestone 400 million years old bones of armoured fish are found.
0:14:06 > 0:14:16The trail winds on through rocks formed in ancient seas - and every 20 feet is another million years.
0:14:28 > 0:14:33The Grand Canyon is really two canyons - one inside the other.
0:14:33 > 0:14:39For a while, the trail flattens out as it approaches the rim of the inner canyon.
0:14:42 > 0:14:53Here, I'm two-thirds the way down - 3,500 feet below the rim and the rocks are 500 million years old.
0:14:53 > 0:15:03The rock has no backboned animals at all - no fish - the only ones are those without backbones,
0:15:03 > 0:15:08including worms which left this tracery of trails.
0:15:33 > 0:15:42At last, the bottom and the Colorado River - it's taken a day to get this far.
0:15:42 > 0:15:49We've ridden 7 miles of trail and have descended that vertical mile into the earth's crust.
0:15:52 > 0:15:58The rocks here are nearly 2,000 million years old.
0:15:58 > 0:16:05For the past 800 feet, they've had no sign of fossils at all.
0:16:05 > 0:16:11For years it was thought that all rocks of this great age had no fossils.
0:16:11 > 0:16:18Why was this? Was it because they were so old they'd had all traces of life crushed from them?
0:16:18 > 0:16:26Or did life really begin with creatures as big as a worm? For years this was a great puzzle.
0:16:26 > 0:16:33Then 20 years ago, people realised they'd been looking in the wrong rocks and in the wrong way.
0:16:41 > 0:16:49These are the right rocks - a kind of flint called chert - at Lake Superior in Canada.
0:16:49 > 0:16:54It's 1,000 miles east and north of the Grand Canyon.
0:16:54 > 0:17:01They were well known in the last century - pioneers used them in their flintlock guns.
0:17:01 > 0:17:07Scientists have recognised for a long time they were extremely ancient rocks.
0:17:07 > 0:17:16We now know they're the same age as those in the bottom of the Grand Canyon - 2,000 million years.
0:17:16 > 0:17:25But- these strange rings in them - these were a subject of great controversy.
0:17:25 > 0:17:31Some maintained they were a sign of very early life.
0:17:31 > 0:17:38Others said they were ordinary chemical processes in the rock's formation.
0:17:38 > 0:17:43Then, in the 1950s, scientists started looking at them in the right way.
0:17:52 > 0:17:56First you cut a wafer-thin slice.
0:17:58 > 0:18:02This is ground down for several hours.
0:18:10 > 0:18:16When scientists first prepared chert to look at through the microscope,
0:18:16 > 0:18:23many people doubted that primitive forms of life could possibly be preserved as tiny fossils.
0:18:26 > 0:18:28Then scientists saw this.
0:18:31 > 0:18:37Marks in rock can be deceptive - they may be the result of mineral action.
0:18:37 > 0:18:42But these filaments are almost identical to algae growing today.
0:18:51 > 0:18:57Soon fossils of other primitive life were found, that once lived in those early seas.
0:19:04 > 0:19:08Other micro-fossils have been found -
0:19:08 > 0:19:14in rocks even older - 3,000 million years old.
0:19:14 > 0:19:24These immense periods baffle the imagination, but we get an idea of relative lengths of the stages,
0:19:24 > 0:19:33if we condense the history of life on earth into one year - then 10 million years become one day.
0:19:33 > 0:19:45On that calendar, I talk in the last moment of Dec 31, man arrived a few hours ago in the afternoon.
0:19:45 > 0:19:51The first backboned animal crawled on to land in the last week of November,
0:19:51 > 0:19:57and these gunflint cherts were formed on June 15th.
0:19:57 > 0:20:05Now let's go back, way, way, to the beginning of January, to the beginning of life.
0:20:14 > 0:20:203500 million years ago, our planet was very different from the one we live on today.
0:20:24 > 0:20:29Erupting volcanoes built islands of lava and ash in the seas.
0:20:29 > 0:20:36The atmosphere was filled with gases, such as ammonia, methane, hydrogen and steam.
0:20:45 > 0:20:51There was no oxygen - so consequently there was no ozone,
0:20:51 > 0:20:55so ultra-violet rays bathed the young planet.
0:21:34 > 0:21:40Carbon compounds formed including amino acids - the building blocks of protein.
0:21:45 > 0:21:52For millions of years, the chemical soup thickened and changed, possibly added to from outer space.
0:21:56 > 0:22:02Some compounds aggregated in droplets, with a membrane through which other chemicals could pass.
0:22:13 > 0:22:19Eventually, large molecules appeared with extraordinary characteristics.
0:22:19 > 0:22:26They caused amino acids to form round them and so built proteins but also produced copies of themselves.
0:22:28 > 0:22:33Such a molecule - DNA - is at the centre of every life cell.
0:22:33 > 0:22:39Its shape is a double spiral linked by chemical units of four kinds.
0:22:39 > 0:22:46Their arrangement acts as a code for production of protein and a group in DNA is called a gene.
0:22:49 > 0:22:58On occasion, the DNA unzips and each half attracts the correct chemical units and forms two new molecules.
0:22:58 > 0:23:05When this first happened, primitive cells formed new cells and life on earth had appeared.
0:23:08 > 0:23:18Sometimes a mistake can cause variations in first cells and natural selection sorted them out.
0:23:20 > 0:23:26Those best suited to their environment survived - the rest died.
0:23:35 > 0:23:45So, over tens of millions of years, new organisms developed and invaded new environments on earth.
0:23:49 > 0:23:52Evolution had truly begun.
0:24:03 > 0:24:11We can glimpse what early life was like, in the hot springs of Yellowstone Park in Wyoming.
0:24:19 > 0:24:24These springs are stained a variety of colour
0:24:24 > 0:24:31by micro-organisms that look to be identical with some of the earliest fossils that we know.
0:24:33 > 0:24:37Tufts of bacteria grow where the water's hottest.
0:24:40 > 0:24:47In cooler areas, other bacteria deposit silica, in strange coloured crusts.
0:24:50 > 0:24:53They represent the next big step.
0:24:54 > 0:24:58They're probably like the first forms to manufacture food
0:24:58 > 0:25:04inside their cell walls, with the aid of energy from the sun - light.
0:25:06 > 0:25:12One of the raw materials needed was hydrogen and at first they got it as sulphuretted hydrogen.
0:25:12 > 0:25:20It occurs in volcanic gases - there's some around here - it smells a bit of rotten eggs.
0:25:20 > 0:25:26And indeed, there's such bacteria flourishing in the hot water of these springs.
0:25:26 > 0:25:33Then that link with volcanoes was broken and forms of bacteria arose which got their hydrogen
0:25:33 > 0:25:41from a more widespread and easily available source - from water and it was a crucial stage in life.
0:25:41 > 0:25:48Because if you take hydrogen from water, you're left as a by-product with oxygen.
0:25:58 > 0:26:01These new bacteria still exist
0:26:01 > 0:26:05as slime on rocks or in ponds covered with silver bubbles.
0:26:05 > 0:26:10It was they that first contributed oxygen to the atmosphere.
0:26:11 > 0:26:16Under the microscope, they're seen as very simple structures.
0:26:18 > 0:26:23Some form chains - others isolated beads.
0:26:29 > 0:26:36On a larger scale, they form mats of bacteria in the cooler springs of Yellowstone.
0:26:42 > 0:26:48Some of these bluegreens deposit lime as part of the chemistry of their body processes.
0:26:48 > 0:26:58In one place in the world - a bay off Western Australia, they grow huge and form these pillars.
0:26:59 > 0:27:07What makes this special, is the mouth of the bay is almost blocked by a bar of sand and sea grass.
0:27:07 > 0:27:15This restricts the flow of the tide in and out, with a result that these waters are extremely salty.
0:27:15 > 0:27:21Virtually none of the creatures which eat bluegreens can survive here.
0:27:21 > 0:27:26So the bluegreens, primitive organisms, can grow uncropped,
0:27:26 > 0:27:36as when they were an advanced form of life 2000 million years ago, at the beginning of life on earth.
0:27:36 > 0:27:42Here is an explanation for the shapes we saw on the shores of Lake Superior.
0:28:11 > 0:28:18This is as close as we may get to a scene of the world when life was at last beginning to stir.
0:28:23 > 0:28:30Now life had reached the point of no return - the oxygen accumulated and formed ozone in the atmosphere.
0:28:30 > 0:28:34It screened off ultra-violet rays that had helped create life.
0:28:36 > 0:28:41It could never begin in the same way again.
0:28:46 > 0:28:55Things changed little for millions of years but at last came a new and dramatic step.
0:28:57 > 0:29:04To find evidence of that development, you need go no further than your local pond.
0:29:21 > 0:29:29Most microscopic organisms here are single cells, yet each is much more complex than any bacterium.
0:29:32 > 0:29:37Some, like this amoeba, seem to have animal characteristics.
0:29:37 > 0:29:40Some appear to be simple plants.
0:29:41 > 0:29:45Yet others seem to be half animal, half plant.
0:29:52 > 0:29:57Seen through an electron-microscope,
0:29:57 > 0:30:06the DNA is enclosed in its own compartment - other parts resemble and act like, bluegreens.
0:30:09 > 0:30:14They look more like bacteria and are a source of energy.
0:30:18 > 0:30:24This cell's driven by a tail that resembles another bacterium.
0:30:24 > 0:30:29So, it appears, this tiny creature is composed of a committee of smaller ones.
0:30:41 > 0:30:46It took a long time for life to reach this stage.
0:30:46 > 0:30:52Probably not till 1,200 million years ago - say early September in our life-on-earth year.
0:31:00 > 0:31:05These belong to this advanced type - many still abound in fresh water and the sea.
0:31:05 > 0:31:10They form the basic food of other organisms.
0:31:40 > 0:31:43Some have skeletons of silica.
0:31:57 > 0:32:00Another kind with shell of chalk.
0:32:08 > 0:32:12They're like an amoeba to which they're closely related.
0:32:17 > 0:32:21Food is drawn inside.
0:32:29 > 0:32:32They reproduce by splitting in two.
0:32:39 > 0:32:44Some cells have more complicated methods of reproduction.
0:32:45 > 0:32:53These have temporarily joined to exchange genes - later they'll part and divide in the normal way.
0:33:01 > 0:33:09Others shuffle genes and divide so as to produce a special cell with half the genes of the parent -
0:33:09 > 0:33:13these special cells are eggs.
0:33:20 > 0:33:24Others of the species also produce sex cells.
0:33:25 > 0:33:32This time they're quite different in form - they have tails - they're sperm cells.
0:33:37 > 0:33:39They're attracted to the egg.
0:33:40 > 0:33:44The first to find it, penetrates it.
0:33:49 > 0:33:55It swims to the nucleus and unites with it - so the full complement of genes is restored.
0:33:55 > 0:34:00But now it's in a new combination, different from either parent.
0:34:01 > 0:34:07When this developed, the extent and frequency of variation increased.
0:34:10 > 0:34:15The pace of evolution accelerated.
0:34:21 > 0:34:25One of the most successful groups are the ciliates.
0:34:25 > 0:34:31They're covered with hairs, cilia, which drive them through the water.
0:34:31 > 0:34:37They also create currents which waft food into their gullet.
0:35:00 > 0:35:04These ciliates are stalked and anchored to one spot.
0:35:05 > 0:35:09Others are large and mobile and hunt for their food.
0:35:21 > 0:35:23These ciliates are quite large.
0:35:24 > 0:35:27Just visible to the naked eye.
0:35:33 > 0:35:36But size can be got in another way.
0:35:37 > 0:35:41By grouping cells together in an organised colony.
0:35:43 > 0:35:52This, the size of a pinhead, has hundreds of cells with tails, beating in a co-ordinated way.
0:35:58 > 0:36:04Inside, daughter colonies are formed and the delicate globe ruptures to release them.
0:36:13 > 0:36:17A stage further - and sponges appeared.
0:36:24 > 0:36:32There are 5,000 species of sponges today and their bonds are very loose.
0:36:32 > 0:36:38Individual cells may crawl around the surface like amoeba.
0:36:38 > 0:36:43If a sponge is forced through a sieve, so it breaks into separate cells,
0:36:43 > 0:36:46they'll reorganise to form a new sponge.
0:36:48 > 0:36:52What's more, each cell will take its proper place.
0:36:54 > 0:37:01Some form walls, others are pump cells lining channels with which the sponge is riddled.
0:37:03 > 0:37:09By beating their threads, they draw in water through pores on the sides.
0:37:09 > 0:37:14Then pump it out at the top after the food has been strained off.
0:37:16 > 0:37:22The structure's supported by other cells which make tiny needles to form a skeleton.
0:37:23 > 0:37:27In glass sponges, they're made of silica.
0:37:31 > 0:37:39Modern science is only 300 years old, yet it's provided us with profound insights
0:37:39 > 0:37:46into the workings of the world, but there's a lot we don't know - take this sponge skeleton.
0:37:48 > 0:38:01How on earth did the tiny sponge cells collaborate to build from millions of splinters of silica
0:38:01 > 0:38:06this complex, beautiful structure - Venus's Flower-basket?
0:38:08 > 0:38:14Some religious people say it's the work of God and that's all that need be said.
0:38:14 > 0:38:21Some scientists claim that in time we'll provide a more detailed explanation than that.
0:38:21 > 0:38:25Either way, it's an awesome and beautiful object.
0:38:26 > 0:38:30But sponges are a dead end.
0:38:30 > 0:38:35They have no mouth, no gut, no muscles, no nervous system.
0:38:35 > 0:38:38But this has.
0:38:42 > 0:38:50It's a jelly-like creature - just 2 layers of cells - the inner one lines a cavity with an opening.
0:38:53 > 0:38:57It's a fully co-ordinated, multi-celled animal.
0:38:57 > 0:39:01It's one of several comb jellies which swarm in the ocean.
0:39:01 > 0:39:05So transparent they're hardly noticed.
0:39:14 > 0:39:18To appreciate their full beauty, you must use special lighting.
0:40:18 > 0:40:23A Medusa - after the lady in the Greek myth who had snakes on her head for hair.
0:40:24 > 0:40:26Its tentacles have stings for prey.
0:40:38 > 0:40:45Comb jellies and medusae have muscle fibres and a nervous system - and most medusae have a surprise.
0:40:45 > 0:40:48They begin life differently.
0:40:53 > 0:40:56They look like plants - but are animals.
0:40:57 > 0:41:01Each began when a tiny creature developed from the egg of a medusae.
0:41:02 > 0:41:05It settled on the bottom of the sea.
0:41:07 > 0:41:10From it grew a twig bearing polyps.
0:41:23 > 0:41:30Each polyp is a medusa and in some species the medusae bud off the branch and swim away.
0:41:30 > 0:41:33Others are born from special vessels.
0:42:21 > 0:42:28All these medusae, not much bigger than a pinhead, have been produced without sex.
0:42:28 > 0:42:36Later, they develop sexual cells which are released into the sea to produce larvae for new polyps.
0:42:40 > 0:42:47This alternation between sexual and non-sexual means of reproduction
0:42:47 > 0:42:51has given these creatures great scope for variety.
0:43:09 > 0:43:16The larger medusae carry jelly so they're more robust in rough seas - these are the true jellyfish.
0:43:17 > 0:43:24Many lead the same type of double life, having a stationary polyp phase as well as a swimming one.
0:44:31 > 0:44:39It's an obvious deduction that jellyfish appeared very early in the development of life.
0:44:39 > 0:44:46But there was no proof they did - after all, proof could only come from the fossil record.
0:44:46 > 0:44:51and how could such a thing as a jellyfish be fossilised,
0:44:51 > 0:44:59let alone survive in rocks from the earliest period? Then, 30 years ago in these sandstones
0:44:59 > 0:45:09in the Flinders Ranges, Australia - probably 650 million years old - people found things like this.
0:45:15 > 0:45:22At first, many refused to believe these faint impressions were the remains of jellyfish.
0:45:22 > 0:45:28But enough have been found to make quite sure that that's what they are.
0:45:58 > 0:46:03This, a form of jellyfish, isn't a single creature, but a colony of polyps.
0:46:04 > 0:46:09It has gone to sea and has much the same structure as a true jellyfish.
0:46:14 > 0:46:18Another colony built the same way is the Portuguese man o' war.
0:46:19 > 0:46:26It has no swimming bell, but a bag filled with gas that supports the colony.
0:46:37 > 0:46:41Tentacles trail behind for up to 50 metres.
0:46:47 > 0:46:52The colony begins with one member which buds off.
0:46:54 > 0:47:00These, bud off others - some for feeding, some for reproduction, some to catch prey.
0:47:02 > 0:47:07As with all jellyfish and their relatives, the tentacles have special stinging cells.
0:47:07 > 0:47:13Each has a coiled tube which discharges on contact with prey.
0:47:26 > 0:47:31These are complicated creatures and you'd think, recent developments.
0:47:31 > 0:47:37In fact, a fossil from the Flinders Range, suggest they existed 650 million years ago.
0:48:05 > 0:48:12Alongside these jellyfish in the same rocks, are remains of other related creatures.
0:48:14 > 0:48:22These were animals in which a kind of medusa remained small, and joined to form a colony.
0:48:22 > 0:48:33We can be sure of that, because similar creatures are alive today, only 40 miles from here in the sea.
0:48:37 > 0:48:44Sea pens - on either side of the stems are polyps for feeding and reproduction.
0:48:45 > 0:48:49It bears a remarkable resemblance to the fossil.
0:49:12 > 0:49:15These are soft corals.
0:49:16 > 0:49:20Another kind - dead man's fingers.
0:49:25 > 0:49:31Soft corals of all kinds grow in depths of 6,000 metres.
0:49:32 > 0:49:35Stony corals make limestone reefs.
0:49:36 > 0:49:39They live no deeper than 40 metres.
0:49:59 > 0:50:02Cells grow over early ones and stifle them.
0:50:08 > 0:50:11The corals contain plants.
0:50:11 > 0:50:14Tiny, single-celled green algae.
0:50:15 > 0:50:19Like all plants they release oxygen.
0:50:20 > 0:50:26They also assimilate carbon dioxide and that helps the corals to form their skeletons of lime.
0:51:27 > 0:51:33The reef may look like some fantastic, multi-coloured jungle of plants and flowers.
0:51:33 > 0:51:40But when you touch one, it has the hard, incongruous scratch of stone.
0:52:06 > 0:52:14Coral organisms are tiny and simple, yet grow on such a scale and their skeletons are so durable
0:52:14 > 0:52:21that they may well have been the first signs of life that could be detected from outer space.
0:52:21 > 0:52:25Certainly this Great Barrier Reef can be seen from the moon.
0:52:25 > 0:52:32So it may be if an astronaut came this way, several hundreds of millions of years ago,
0:52:32 > 0:52:40he might have noticed, in the seas of the earth, a few mysterious and beautiful shapes in turquoise,
0:52:40 > 0:52:44and guessed that life on earth had really started.
0:54:00 > 0:54:03Subtitles by Bill Northwood - 1982