0:00:05 > 0:00:08Since its emergence more than three billion years ago,
0:00:08 > 0:00:10life on our planet has suffered
0:00:10 > 0:00:13a series of devastating mass extinction events.
0:00:16 > 0:00:19These have killed off uncountable species
0:00:19 > 0:00:22and almost threatened to end life on Earth.
0:00:26 > 0:00:31I'm Professor Richard Fortey of London's Natural History Museum
0:00:31 > 0:00:37and all my life I've studied the remains of animals long extinct.
0:00:39 > 0:00:43'But now, I'm setting off to discover why some animals and plants have survived.'
0:00:43 > 0:00:45Hello, snaky.
0:00:45 > 0:00:49'I'm going in search of living fossils...'
0:00:49 > 0:00:51My goodness. '..Old-timers...'
0:00:51 > 0:00:53Look at this little face.
0:00:53 > 0:00:57'..That somehow managed to survive when so many others perished.'
0:00:57 > 0:00:58Wow.
0:00:58 > 0:01:02Do you know what, I'm used to seeing these things as fossils.
0:01:02 > 0:01:03'In the process,
0:01:03 > 0:01:07'I hope to find an answer to one of the most profound questions of all.'
0:01:08 > 0:01:13Is being a survivor a question of having some very special features?
0:01:15 > 0:01:17Or nothing more than pure chance?
0:01:19 > 0:01:24'From living fossils that are our most ancient relations...
0:01:26 > 0:01:30'..to gigantic relics from the age of dinosaurs.'
0:01:30 > 0:01:33Life as we see it today is not just the product
0:01:33 > 0:01:35of the processes of evolution,
0:01:35 > 0:01:38it is also a consequence of mass extinction.
0:01:39 > 0:01:42We are all the sons and daughters of catastrophe.
0:01:59 > 0:02:04It's an early evening in late May. The tide is high.
0:02:04 > 0:02:06Tonight, there will be no moon.
0:02:07 > 0:02:10'Here, together with local naturalist Glenn Gauvry,
0:02:10 > 0:02:12'I'm about to witness an annual event
0:02:12 > 0:02:15'unlike any other in the animal kingdom.
0:02:15 > 0:02:19'And one I've been waiting to see all my life.'
0:02:20 > 0:02:24You know, Glenn, for a palaeontologist to come here
0:02:24 > 0:02:26is rather like a Muslim going to Mecca,
0:02:26 > 0:02:29or a Catholic going to see the Pope.
0:02:29 > 0:02:30It is a special place.
0:02:30 > 0:02:34Actually, probably the most productive place in the world
0:02:34 > 0:02:36to see what we're getting ready to see.
0:02:36 > 0:02:38Can I, dare I, ask how many are going to be there?
0:02:38 > 0:02:42- Oh, a lot more than you can imagine. - Well, I can't wait to see them.
0:02:42 > 0:02:45It's a perfect night and it's calm. It's going to be quite spectacular.
0:02:48 > 0:02:50Richard, wait till you see this.
0:02:50 > 0:02:53- Look over there. - Heavens above.- Isn't it amazing?
0:02:56 > 0:02:57'In the darkness,
0:02:57 > 0:03:02'low, shelly mounds, the size of inverted colanders, loom into view.
0:03:03 > 0:03:06'The horseshoe crab, an ancient survivor
0:03:06 > 0:03:09'whose ancestors were swimming in shallow seas
0:03:09 > 0:03:13'even before the first life struggled onto land.'
0:03:19 > 0:03:25Well, for once, you can use the overused word "primeval".
0:03:25 > 0:03:28- And it's absolutely spot on. - Yeah, it is here.
0:03:28 > 0:03:31- Well, of course, they're here to do business, aren't they?- Yup.
0:03:31 > 0:03:32Mating.
0:03:35 > 0:03:37Look how many males are around this female.
0:03:37 > 0:03:39There's one female right down here.
0:03:39 > 0:03:43So, she's bearing her eggs, the males are trying to fertilise them.
0:03:43 > 0:03:45Yup, and they're probably all doing it at the same time,
0:03:45 > 0:03:48probably all releasing sperm at the same time.
0:03:48 > 0:03:50- So, we're really looking at an orgy, here.- Yeah.
0:03:53 > 0:03:57'This orgy is being repeated all along America's east coast,
0:03:57 > 0:03:59'from here in Delaware to Florida.
0:04:01 > 0:04:04'An ancient ritual that has been going on every year
0:04:04 > 0:04:07'since long before the dinosaurs.
0:04:11 > 0:04:16'The poor, exhausted females are amply over-provided with mates.'
0:04:18 > 0:04:21We've got one female here and one female here
0:04:21 > 0:04:25and the rest of those are all males around those two females.
0:04:28 > 0:04:31'The moist sand stops their gills drying out.
0:04:31 > 0:04:34'And they may, eventually, struggle back to the sea
0:04:34 > 0:04:35'when the laying is done.
0:04:37 > 0:04:38'Although many do not.'
0:04:42 > 0:04:46The fossil record shows the horseshoe crab is a survivor
0:04:46 > 0:04:50from the greatest extinction event in the history of our planet.
0:04:53 > 0:04:55250 million years ago,
0:04:55 > 0:04:57during the Permian Age,
0:04:57 > 0:05:01the continents were combined into a single landmass.
0:05:01 > 0:05:04Terrestrial climate was greatly affected
0:05:04 > 0:05:07and tough, arid conditions became widespread.
0:05:07 > 0:05:10'Animals that might have prospered separately
0:05:10 > 0:05:14'now came into direct competition.
0:05:14 > 0:05:15'As a result, many died out.
0:05:17 > 0:05:20'But it was much worse than that.'
0:05:23 > 0:05:26At the same time, there was a volcanic event
0:05:26 > 0:05:28of unimaginable scale.
0:05:30 > 0:05:32It was one of the greatest outpourings of lava
0:05:32 > 0:05:35in Earth's history.
0:05:35 > 0:05:38For half a million years, more than a million square kilometres
0:05:38 > 0:05:44of the united supercontinent were buried under flow after flow.
0:05:47 > 0:05:51These released vast quantities of ash and gases,
0:05:51 > 0:05:55poisoning the seas and triggering massive climate change.
0:06:01 > 0:06:06Incredibly, the horseshoe crab was a survivor from this -
0:06:06 > 0:06:08the most lethal of all extinction events.
0:06:14 > 0:06:20'The next day, we return to a scene of devastation for some
0:06:20 > 0:06:22'and abundance for others.
0:06:24 > 0:06:28'While dead crab carcasses litter the sandy beach,
0:06:28 > 0:06:29'million upon millions of eggs
0:06:29 > 0:06:32'provide a feast for the migrating birds.
0:06:34 > 0:06:38'Tens of thousands of birds can't make much of an impression
0:06:38 > 0:06:40'on millions of eggs.
0:06:43 > 0:06:46'But ensuring the continuation of the species
0:06:46 > 0:06:49'takes a heavy toll on individuals.'
0:06:52 > 0:06:57- Well, Glenn, this looks like the day after the night before.- Sure does.
0:06:57 > 0:07:01Or a scene after a major battle, doesn't it?
0:07:01 > 0:07:02With these carcasses lying here.
0:07:02 > 0:07:05It's amazing how many are on the beach right now.
0:07:05 > 0:07:09'The night has resulted in many casualties.
0:07:10 > 0:07:13'The carcasses of those that failed to make it back to sea
0:07:13 > 0:07:15'lie scattered all around.
0:07:16 > 0:07:19'Others have hunkered down in wet sand.
0:07:19 > 0:07:22'So long as they can keep their gills even moderately damp,
0:07:22 > 0:07:25'they can survive until the next tide.
0:07:28 > 0:07:30'This gives Glenn an opportunity to show me
0:07:30 > 0:07:34'how horseshoe crab reproduction has been key to its survival
0:07:34 > 0:07:36'for nearly half a billion years.'
0:07:39 > 0:07:43- Is that a female there?- It is. She's been buried down since the last tide.
0:07:43 > 0:07:46- Would she mind being dug up, do you think?- Probably not.
0:07:46 > 0:07:48Look, she's got some nice spawning scars, there.
0:07:49 > 0:07:51Let's pick her up.
0:07:51 > 0:07:56- Here we go.- Sorry, old girl. If I...- Shall I hold this down?
0:07:56 > 0:07:59- You want to lift up the operculum? - If I keep up that...
0:07:59 > 0:08:03If she's got eggs, you can sometimes encourage some of them to come out.
0:08:04 > 0:08:08- There we go.- They're like caviar, really, about the same size.
0:08:08 > 0:08:12- I haven't tasted them myself. - I haven't either. Other people have.
0:08:14 > 0:08:18'Each female lays up to 20 clutches of several thousand eggs.
0:08:20 > 0:08:25'Although only a few will even get to hatch, such a vast quantity
0:08:25 > 0:08:28'ensures the horseshoe crab is amongst our great survivors.'
0:08:31 > 0:08:36- And while we've got her here, we can see the other limbs here.- Yup.
0:08:36 > 0:08:39The legs, which seem exceedingly strong
0:08:39 > 0:08:41and they can crush a clam if they need to.
0:08:41 > 0:08:44Yeah, if it's not too large. She's pretty feisty.
0:08:44 > 0:08:45Pretty feisty, this one.
0:08:45 > 0:08:48- Her mouth right in the centre, right there.- That's where the mouth is.
0:08:48 > 0:08:51And they can eat almost anything that's got some nourishment in it?
0:08:51 > 0:08:55They're opportunistic feeders. They love little clams and mussels
0:08:55 > 0:08:58but if there's a dead fish, they'll go over and they'll eat that as well.
0:08:58 > 0:09:01They're just not an aggressive animal,
0:09:01 > 0:09:03so they can't chase after anything.
0:09:03 > 0:09:05So, that lack of choosiness might also be a factor
0:09:05 > 0:09:07in their survivability.
0:09:07 > 0:09:10Well, I think being a generalist is a good strategy.
0:09:10 > 0:09:12I mean, it's just like going to a restaurant.
0:09:12 > 0:09:15If you can eat anything on the menu, you're going to go out full.
0:09:15 > 0:09:17That's right!
0:09:17 > 0:09:20I think we should give her a chance to get a bit of oxygen back in her.
0:09:20 > 0:09:24- I agree.- And there she goes. - She was rather accommodating.
0:09:24 > 0:09:27- Thank you, girl.- Thank you. Thank you very much.
0:09:27 > 0:09:29'Unfussy diet and a scattergun approach
0:09:29 > 0:09:34'to reproduction are two good strategies for a species to survive.
0:09:34 > 0:09:40'But even better is being virtually indestructible.'
0:09:40 > 0:09:42Look, he's missing his tail.
0:09:42 > 0:09:45And he's got this huge damaged area, right there.
0:09:45 > 0:09:48- This is why they're so incredibly tough.- It is.
0:09:48 > 0:09:51And this must be one of the reasons for their durability
0:09:51 > 0:09:55- and capacity to survive.- It is.
0:09:55 > 0:09:58Look at this one, up here. Look at the concaved area on the front.
0:09:58 > 0:10:02Yeah, that one's really been, that's really been through the wars.
0:10:02 > 0:10:06- Look how deep this concaved area is. - And they can carry on carrying on.
0:10:06 > 0:10:10- Yeah.- So, durability, really, is the name of the game.
0:10:10 > 0:10:12But they do have something to help them.
0:10:12 > 0:10:15- Which is special blood.- Their blood.
0:10:15 > 0:10:17Their copper-based blood, which is blue.
0:10:17 > 0:10:19Actually, it's a very pretty blue.
0:10:19 > 0:10:22- It's almost the colour of your shirt when it hits the light.- Yeah.
0:10:22 > 0:10:29- It's a really nice blue.- And that has the capacity to coagulate.
0:10:29 > 0:10:33- So, they can kind of wall-off a wound.- Yes.- And keep on trucking.
0:10:33 > 0:10:36Yup, they'll pretty much say, "You can have this part of me
0:10:36 > 0:10:38"but you can't have that part of me."
0:10:41 > 0:10:44'As well as its amazing power to coagulate,
0:10:44 > 0:10:46'copper-based blood is also more efficient
0:10:46 > 0:10:51'than ordinary iron-based blood in oxygen-poor environments.
0:10:54 > 0:10:57'This would have been a life-saving quality
0:10:57 > 0:11:00'when the atmosphere and oceans turned toxic
0:11:00 > 0:11:03'during what's usually known as the Great Dying.'
0:11:08 > 0:11:14250 million years ago, life almost died.
0:11:14 > 0:11:1790% of the animals living in the oceans,
0:11:17 > 0:11:19the poisoned oceans, became extinct.
0:11:21 > 0:11:25Yet, somehow, the ancestors of the horseshoe crab negotiated
0:11:25 > 0:11:27this terrible time.
0:11:27 > 0:11:31They aren't actually found at the critical interval.
0:11:31 > 0:11:34They're known before, they're known after.
0:11:34 > 0:11:37They reappear like Lazarus from the dead.
0:11:37 > 0:11:40For that reason, they're sometimes called Lazarus taxon.
0:11:42 > 0:11:44The horseshoe crab wasn't the only species
0:11:44 > 0:11:48to have seemingly returned from the dead
0:11:48 > 0:11:50all those millions of years ago.
0:11:56 > 0:12:00During the Great Dying, many other species also vanished.
0:12:01 > 0:12:05They either became extinct, or dwindled to such small numbers
0:12:05 > 0:12:08they left no fossil record we have ever found.
0:12:10 > 0:12:13They were casualties of the massive volcanism
0:12:13 > 0:12:15that afflicted our planet,
0:12:15 > 0:12:19creating a lethal brew of toxicity and climate change
0:12:19 > 0:12:21that made it almost uninhabitable.
0:12:25 > 0:12:28Rocks preserve the evidence of ancient landscapes
0:12:28 > 0:12:29and vanished lives.
0:12:33 > 0:12:36'In special places around the world, we can still find evidence
0:12:36 > 0:12:41'for living things far more ancient even than horseshoe crabs.
0:12:41 > 0:12:44'Living things whose ancestors are even older
0:12:44 > 0:12:47'than these ancient mountains
0:12:47 > 0:12:50'once intruded as liquid rock into the depths of the Earth.'
0:12:58 > 0:13:00They look almost like Henry Moore sculptures,
0:13:00 > 0:13:03these fretted pieces of rock -
0:13:03 > 0:13:06all that's left of a vast mass of granite
0:13:06 > 0:13:09that might have stretched for many, many miles.
0:13:09 > 0:13:12And, of course, once buried deep beneath the earth.
0:13:13 > 0:13:17So, everything above, everything above has been eroded away.
0:13:20 > 0:13:24'The Remarkable Rocks at the southern tip of South Australia
0:13:24 > 0:13:27'are 500 million-year-old granites.
0:13:27 > 0:13:29'One of the toughest rocks.'
0:13:33 > 0:13:37Some of our survivors are as durable as this granite.
0:13:37 > 0:13:40They have lasted for hundreds of millions of years,
0:13:40 > 0:13:43but yet they are not entirely unchanged -
0:13:43 > 0:13:45nothing in nature is ever entirely unchanged.
0:13:45 > 0:13:48These rocks have been sculpted by natural forces.
0:13:49 > 0:13:54And our organisms have continued to evolve in subtle ways,
0:13:54 > 0:13:57while still retaining ancient features
0:13:57 > 0:13:59that tell us of deep time and vanished worlds.
0:14:01 > 0:14:04'In search of these ancient organisms
0:14:04 > 0:14:07'and how they have changed over the ages,
0:14:07 > 0:14:09'I take a journey backwards in time.
0:14:15 > 0:14:19'Just a few miles away is one of the best fossil sites in the world.
0:14:21 > 0:14:23'Emu Bay is owned by farmer Paul Buck.'
0:14:28 > 0:14:30Here, just...
0:14:30 > 0:14:34'My old friend Jim Jago has been coming here ever since the time
0:14:34 > 0:14:40'of Paul's father, who discovered the fossils way back in the 1950s.'
0:14:40 > 0:14:42It's places like this that provide us
0:14:42 > 0:14:46with the geological evidence for our survivors.
0:14:46 > 0:14:49Some of the animals living here have been extinct
0:14:49 > 0:14:52for tens, if not hundreds, of millions of years.
0:14:52 > 0:14:56But some of them still have living relatives.
0:14:56 > 0:14:59Those are the ones we're going to investigate.
0:15:01 > 0:15:03'Buried here are fossils of many of the organisms
0:15:03 > 0:15:05'I hope to search out.
0:15:05 > 0:15:09'As well as evidence of one that didn't make it.
0:15:10 > 0:15:14'Discovered during his last dig just a few weeks earlier,
0:15:14 > 0:15:16'is a fossil specimen of a creature
0:15:16 > 0:15:19'I have spent most of my professional life studying.'
0:15:19 > 0:15:23- Carefully pull this back.- Wow! 'The trilobite.'
0:15:23 > 0:15:26- That's enormous! - We've measured it.
0:15:26 > 0:15:28- It's about 24, 25 centimetres long. - That's huge.
0:15:28 > 0:15:30You know, we tend to think of trilobites
0:15:30 > 0:15:33as little, tiny things in the middle of our hands,
0:15:33 > 0:15:37but they grew to really quite a substantial size, didn't they?
0:15:37 > 0:15:39Yes. This is about as big as they get here.
0:15:39 > 0:15:41I've never seen one any bigger than this.
0:15:44 > 0:15:47'Trilobites survived for hundreds of millions of years,
0:15:47 > 0:15:51'evolved into all sorts of elaborate species.
0:15:51 > 0:15:54'But then, were laid low before the Great Dying.'
0:15:57 > 0:15:59'But although trilobites didn't make it,
0:15:59 > 0:16:02'swimming alongside them were the aquatic ancestors
0:16:02 > 0:16:04'of the scorpion.
0:16:05 > 0:16:09'The largest species of sea scorpions grew as big as a man.
0:16:10 > 0:16:14'Then, around 300 million years ago, some of their smaller cousins
0:16:14 > 0:16:18'were among the earliest creatures to scurry onto land.
0:16:21 > 0:16:26'By the time of the Great Dying, scorpions had adapted to deserts,
0:16:26 > 0:16:29'making them perfectly suited to the arid conditions
0:16:29 > 0:16:32'that spread over the newly-formed supercontinent
0:16:32 > 0:16:34'250 million years ago.
0:16:39 > 0:16:41'They've been adapting ever since.
0:16:41 > 0:16:44'They can now make their homes almost anywhere.
0:16:44 > 0:16:47'Including hotel rooms.'
0:16:47 > 0:16:50The scorpion is another survivor
0:16:50 > 0:16:53that passed through major extinction events,
0:16:53 > 0:16:56probably because it lived in a habitat
0:16:56 > 0:17:03where it didn't worry about arid conditions and changes in climate
0:17:03 > 0:17:08and habitat that extinguished so many of its contemporaries.
0:17:08 > 0:17:13They have their sting, of course, in the tail which they can arch over
0:17:13 > 0:17:16to administer venom to unfortunate prey.
0:17:22 > 0:17:26'Today, there are scorpions that can tolerate not just heat,
0:17:26 > 0:17:31'but freezing temperatures as cold as -30, live to be 30 years old
0:17:31 > 0:17:33'and go for 12 months without feeding.'
0:17:40 > 0:17:46The scorpion is a real survivor and I intend to survive this encounter.
0:17:46 > 0:17:50So, we're going to bring this take to a speedy conclusion.
0:17:51 > 0:17:53Exit stage left! Ha-ha.
0:18:06 > 0:18:07Whoops.
0:18:13 > 0:18:17Even before relatives of the scorpions crawled onto land,
0:18:17 > 0:18:19it was already clothed with plants.
0:18:21 > 0:18:24It was not long before lush forests appeared -
0:18:24 > 0:18:27the source of what became coal.
0:18:28 > 0:18:30They endured for millions of years,
0:18:30 > 0:18:33though the mighty trees that flourished
0:18:33 > 0:18:36'in early, damp forests could not survive the increasing aridity
0:18:36 > 0:18:42of the Earth's landmasses coming together into one supercontinent.
0:18:43 > 0:18:46But, amazingly, some humble survivors
0:18:46 > 0:18:50are relatives of these extinct giants,
0:18:50 > 0:18:52and still lurk in secret corners of the world.
0:19:03 > 0:19:07The Daintree Rainforest of northern Queensland is probably
0:19:07 > 0:19:10the oldest tropical rainforest in the world.
0:19:12 > 0:19:15A habitat that has remained largely unchanged
0:19:15 > 0:19:16for tens of millions of years.
0:19:21 > 0:19:27We're in Daintree, a very special tropical rainforest,
0:19:27 > 0:19:32in which are hiding some plants that have been with us on the planet
0:19:32 > 0:19:34for more than 250 million years.
0:19:34 > 0:19:37It's a place of survivors, and we're going to try
0:19:37 > 0:19:40and find some, living in their natural habitat.
0:19:43 > 0:19:47'Daintree still hides relatives of some of the first plants
0:19:47 > 0:19:48'to colonise the land.
0:19:50 > 0:19:53'Today, the vast majority of all plants are vascular.
0:19:54 > 0:19:57'That is, they use veins to transport nutrients
0:19:57 > 0:19:59'towards the growing shoot.
0:20:02 > 0:20:05'Among the first vascular plants were lycopods.
0:20:07 > 0:20:09'Normally, they're ground-dwelling,
0:20:09 > 0:20:13'but to find one, I venture under the forest canopy
0:20:13 > 0:20:16'to meet a botanist with the rather appropriate name
0:20:16 > 0:20:18'of Dr Ashley Field.'
0:20:19 > 0:20:25- Ah, Ashley, how's it going? - Good, you've made it in.- I have.
0:20:25 > 0:20:29Well, I've been walking through the bush looking for lycopods.
0:20:29 > 0:20:32- For lycopods?- And I can't find any.
0:20:32 > 0:20:35Well, that's because your eyes are glued to the ground.
0:20:35 > 0:20:39The lycopods here are way up above us in the canopy.
0:20:39 > 0:20:42If you follow this tree up, you can see a clump of a plant
0:20:42 > 0:20:45that's hanging down with branches dividing.
0:20:45 > 0:20:48It's a soft, fern-like plant. That is a tropical lycopod.
0:20:48 > 0:20:51That's an epiphytic Huperzia.
0:20:51 > 0:20:55What's the right thing about the habitat up there that suits them?
0:20:55 > 0:20:59They're high up in the trees because they need a lot of light
0:20:59 > 0:21:03and there's three or four good host trees just in this small cluster.
0:21:03 > 0:21:07- So, they don't occur everywhere. - I'm looking forward to seeing one.
0:21:07 > 0:21:10Well, what I'll do is I'll go up to this one, just up here,
0:21:10 > 0:21:12and see if I can get a small sample to show you,
0:21:12 > 0:21:16- because I work on these guys. - That would be great. Good luck.
0:21:18 > 0:21:21'Epiphytic plants live perched upon other plants.
0:21:21 > 0:21:25'But the tiny plant Ashley pursues at such dizzying height
0:21:25 > 0:21:29'once grew to great height itself.
0:21:29 > 0:21:33'350 million years ago, lycopods were trees,
0:21:33 > 0:21:36'the equal of any hereabouts.
0:21:38 > 0:21:40'Now, they're a pale shadow of their former selves
0:21:40 > 0:21:44'and live here, in the branches of other trees.
0:21:44 > 0:21:48'Not as parasites, but as unobtrusive lodgers.
0:21:49 > 0:21:53'Amazingly, they still maintain some of their unique features,
0:21:53 > 0:21:57'even millions of years later and in their miniature version.'
0:21:59 > 0:22:03- Well, welcome back. - Oh, I hope it's in here somewhere.
0:22:03 > 0:22:06Now, this is all I was after, it's a very, very small piece
0:22:06 > 0:22:10for DNA work of an epiphytic Huperzia.
0:22:10 > 0:22:12That one just up there.
0:22:18 > 0:22:20What's the structure at the end, there?
0:22:20 > 0:22:23The structure on the end is a strobilus and in this species
0:22:23 > 0:22:25the strobilus is distinct from the other shape.
0:22:25 > 0:22:27That's the spore body, isn't it?
0:22:27 > 0:22:30The spores are produced in sporangia, which are little capsules
0:22:30 > 0:22:33in under those leaves, there, and many hundreds of them,
0:22:33 > 0:22:36thousands of them, are dispersed by the wind,
0:22:36 > 0:22:39they blow around and, hopefully, land on the right position
0:22:39 > 0:22:41on one of these trees so that they can grow.
0:22:41 > 0:22:43- It's a sort of scattergun approach, really.- It is.
0:22:43 > 0:22:45I mean, spores,
0:22:45 > 0:22:50it's an old solution to a problem of spreading yourself around.
0:22:50 > 0:22:52- It may be old but it works. - It certainly does.
0:22:52 > 0:22:57So, we're talking about something that's pushing on beyond 400 million years.
0:22:57 > 0:23:00- Yeah. Some of the oldest plants around.- Isn't that incredible?- It is.
0:23:00 > 0:23:03Have you a theory why this sort of habitat should suit them?
0:23:03 > 0:23:07The reason this particular place is good is the high rainfall,
0:23:07 > 0:23:10high humidity, and it's been here for a long time.
0:23:10 > 0:23:15That environment's been here long enough for species to establish and stay here.
0:23:15 > 0:23:20And, presumably, it's a case of, "if it ain't broke, don't fix it."
0:23:20 > 0:23:23These things have got a kind of morphology, life habit,
0:23:23 > 0:23:25that can always find a niche somewhere
0:23:25 > 0:23:28- and this is one of those special places.- It certainly is.
0:23:30 > 0:23:33'Their survival may be tied up with their reproduction.
0:23:35 > 0:23:39'Releasing spores onto the wind is one of the oldest
0:23:39 > 0:23:42'and most successful of all methods of reproducing.
0:23:44 > 0:23:48'It has been repeated numerous times with numerous plant species
0:23:48 > 0:23:49'ever since.
0:23:52 > 0:23:55'But enduring by being smuggled through time
0:23:55 > 0:23:59'on the back of another species is usually a survival strategy
0:23:59 > 0:24:01'adopted by different types of organisms.
0:24:01 > 0:24:03'Parasites.
0:24:04 > 0:24:06'And it is one of the oldest
0:24:06 > 0:24:09'and most persistent parasites that is my next survivor.
0:24:15 > 0:24:18'Its home is the English countryside.
0:24:20 > 0:24:23'But not on land. We're heading back in time
0:24:23 > 0:24:25'and into water, where life began.
0:24:28 > 0:24:32'It's a species currently being sought by Adam Hilliard
0:24:32 > 0:24:35'and his team from the UK Environmental Agency.'
0:24:40 > 0:24:43We come on a beautiful spring day to this beautiful,
0:24:43 > 0:24:49clear, chalk stream in search of a very special old-timer.
0:24:49 > 0:24:50A fish.
0:24:52 > 0:24:57A fish that has survived for more than 400 million years.
0:24:59 > 0:25:02'It's a creature that resembles an eel
0:25:02 > 0:25:04'but is, in fact, a jawless fish.'
0:25:08 > 0:25:11Well, this is rather an inelegant
0:25:11 > 0:25:14but no doubt very effective way of fishing.
0:25:14 > 0:25:16How does it work? What are you doing?
0:25:16 > 0:25:19Basically, we're doing an electric fishing survey.
0:25:19 > 0:25:22On our boat, there, we've got a generator which provides power
0:25:22 > 0:25:25to the control box at the front of the boat, there.
0:25:25 > 0:25:28And then the control box feeds the power out to the electrodes,
0:25:28 > 0:25:31the anodes we've got here and the cathode at the back,
0:25:31 > 0:25:33the positive and the negative.
0:25:33 > 0:25:35The fish are attracted towards the anodes here.
0:25:35 > 0:25:38We then net the fish out, put them into an aerated bin
0:25:38 > 0:25:40and do that over a 100-metre stretch
0:25:40 > 0:25:44and we can work out numbers of fish and weight of fish within that area.
0:25:44 > 0:25:47- So, you're doing a kind of census? - Effectively, yeah.
0:25:47 > 0:25:50We look at the numbers of fish, the diversity of the fish.
0:25:50 > 0:25:52We've caught five different species today.
0:25:52 > 0:25:55Brown trout, bullhead, stickleback, grayling and, of course,
0:25:55 > 0:25:58the brook lamprey as well.
0:25:58 > 0:26:01This is one of the very few habitats in which it successfully lives.
0:26:01 > 0:26:03- Yeah.- Why do you think that is?
0:26:03 > 0:26:06Well, the River Lambourn is a very clean water source.
0:26:06 > 0:26:09It's got very good habitats for the lamprey's sort of
0:26:09 > 0:26:13various life stages. The sort of larval stage where they live in silt,
0:26:13 > 0:26:16and the adult stages where they spawn and produce the eggs
0:26:16 > 0:26:18which the larval form come from.
0:26:18 > 0:26:22So, this place, as well as being beautiful
0:26:22 > 0:26:24is rather a special conservation area.
0:26:24 > 0:26:27It is, yes. It's a special area of conservation.
0:26:27 > 0:26:30- OK, well, thank you, Adam. I'd better let you get on with it.- OK.
0:26:33 > 0:26:36'Regrettably, although the purity of the water is as good
0:26:36 > 0:26:38'as it ever was,
0:26:38 > 0:26:40'brook lamprey numbers have declined in recent years
0:26:40 > 0:26:45'as foreign invaders, like these North American crayfish,
0:26:45 > 0:26:48'have colonised their habitat.
0:26:50 > 0:26:53'But the lamprey burrow down here,
0:26:53 > 0:26:57'their young living on microscopic algae.'
0:27:02 > 0:27:07We're going to try and catch one of these slippery customers.
0:27:07 > 0:27:11But it's not as easy as you might think. How are we doing, Adam?
0:27:12 > 0:27:15Um, not so good at the moment.
0:27:16 > 0:27:19- Ah, well done.- There we go. - Now, is it a grown-up?
0:27:19 > 0:27:24- This is an adult brook lamprey, yes. - Oh, excellent. Can I have a look?
0:27:25 > 0:27:29- An adult brook lamprey. - Oh, my goodness, it's about...
0:27:32 > 0:27:33Can you sort of...?
0:27:38 > 0:27:42Perhaps we'll have better luck next time. Let's have another go.
0:27:44 > 0:27:47- There you go.- There, oh, ah, yes. There we are.
0:27:47 > 0:27:50It's a charming, little creature.
0:27:50 > 0:27:54And I think this one's a little bit calmer. You can see its, kind of,
0:27:54 > 0:28:01eel-like body, but can you see its little head is sucking onto my hand?
0:28:01 > 0:28:04With a special adaptation at the mouth end.
0:28:04 > 0:28:09It hasn't got a proper jaw at all but it has got little teeth.
0:28:09 > 0:28:13This is a very harmless relative of a rather more sinister animal
0:28:13 > 0:28:16that lives in bigger rivers and seas
0:28:16 > 0:28:20that lives by being a parasite on other fish.
0:28:20 > 0:28:24It rasps with its suckers into the flesh of the fish.
0:28:26 > 0:28:30'The ancient ancestors of the brook lamprey possibly survived
0:28:30 > 0:28:35'the toxic waters of the Great Dying by using the same survival tactic
0:28:35 > 0:28:37'as modern sea lamprey.
0:28:39 > 0:28:43'They use their jawless mouths to rasp onto other fish,
0:28:43 > 0:28:46'burrowing into their flesh.
0:28:48 > 0:28:51'As long as there were other fish to prey on,
0:28:51 > 0:28:54'there would surely be lampreys.'
0:28:54 > 0:28:58I can see it gasping for air, can you? Poor little thing.
0:28:58 > 0:29:02I think I maybe ought to put it back into its natural medium, don't you?
0:29:02 > 0:29:06And leave it to live another 400 million years, let's hope.
0:29:14 > 0:29:16The animals and plants we've seen so far
0:29:16 > 0:29:18prove the importance of one thing.
0:29:18 > 0:29:20Habitat.
0:29:20 > 0:29:23But as well as pure streams and rainforests,
0:29:23 > 0:29:27you can find survivors, sometimes, in the most unexpected places.
0:29:38 > 0:29:42'Hong Kong is one of the most densely-populated areas
0:29:42 > 0:29:44'in the world.
0:29:44 > 0:29:48'There are more skyscrapers here than any other place on Earth.
0:29:50 > 0:29:53'And much of the city is built on land reclaimed from the sea.
0:29:58 > 0:30:02'Yet, some truly ancient survivors are still to be found
0:30:02 > 0:30:06'lurking in the waters off this cramped island.
0:30:07 > 0:30:10'First is a sea creature related to the lamprey.
0:30:12 > 0:30:15'It's commonly called the lancelet.
0:30:15 > 0:30:19'And, believe it or not, it's one of our most distant ancestors.
0:30:21 > 0:30:23'To find it, I join an old friend,
0:30:23 > 0:30:26'Dr Paul Shin of Hong Kong University.
0:30:27 > 0:30:30'Together, we must dare the seaworthiness
0:30:30 > 0:30:32'of a local fishing boat.
0:30:34 > 0:30:39'At the rear of the boat, which doubles as our host's home,
0:30:39 > 0:30:41'the family has a Daoist shrine.
0:30:43 > 0:30:48'They light traditional incense sticks to bless our journey.
0:30:48 > 0:30:53'The South China Seas can be choppy and unpredictable.'
0:30:53 > 0:30:55OK, lower.
0:30:58 > 0:31:00'Finally, when we reach our destination,
0:31:00 > 0:31:03'it's time to lower the steel jaws of the dredger
0:31:03 > 0:31:07'to the sandy seafloor in the hope it will trap our quarry,
0:31:07 > 0:31:09'the lancelet.'
0:31:11 > 0:31:13So, the lancelet is another animal
0:31:13 > 0:31:15that's survived for 500 million years.
0:31:15 > 0:31:17- Exactly.- In this special place.
0:31:17 > 0:31:20What's special about this habitat, do you think?
0:31:40 > 0:31:41So, the animal literally
0:31:41 > 0:31:44gathers food from the surrounding waters and lives on that?
0:31:44 > 0:31:46Yes.
0:31:46 > 0:31:49And they grow and reproduce in this very special habitat.
0:32:28 > 0:32:32'The sandy waters turn up a variety of different,
0:32:32 > 0:32:34'as well as ancient, sealife.
0:32:34 > 0:32:36'Here are tiny sea urchins,
0:32:36 > 0:32:40'whose relatives survived from the age of dinosaurs.
0:32:46 > 0:32:50'But after much frantic dredging and dedicated shifting
0:32:50 > 0:32:54'and sieving, at last, one of us finds the elusive lancelet.
0:32:58 > 0:33:01'We've struck survivor gold.'
0:33:06 > 0:33:10It's an extraordinary thought that a creature so delicate,
0:33:10 > 0:33:16so fragile, could last for such an inconceivably long period of time.
0:33:16 > 0:33:20And yet, that's exactly what has happened with the lancelet.
0:33:20 > 0:33:22Particularly when you compare it
0:33:22 > 0:33:26with the big, Sherman tank-like horseshoe crab.
0:33:26 > 0:33:31But, even more extraordinary, this little, tiny, fragile animal
0:33:31 > 0:33:35is probably the nearest thing we have to our own, distant ancestor.
0:33:45 > 0:33:50Here, Richard, you can see now, a very nice part of the lancelet.
0:33:50 > 0:33:52Can you see?
0:33:54 > 0:33:57Oh, yeah. That's very, very nice indeed.
0:33:58 > 0:34:01'In search of what makes this tiny ancestor of ours
0:34:01 > 0:34:07'such a determined survivor, we return to Paul's lab.'
0:34:09 > 0:34:10This is the lancelet,
0:34:10 > 0:34:14and it's been stained to reveal some of its internal structure.
0:34:14 > 0:34:18And the head end is this end
0:34:18 > 0:34:22and the most important feature is probably the notochord,
0:34:22 > 0:34:25which is this little, tubular structure at the front end.
0:34:25 > 0:34:28This is the feature that connects us
0:34:28 > 0:34:33with all other chordates including vertebrates,
0:34:33 > 0:34:36- like fish, mammals and other organisms.- That's right.
0:34:36 > 0:34:39And above the notochord is the nerve cord.
0:34:39 > 0:34:43- And that runs all the way along the back.- That's correct.
0:34:43 > 0:34:45This is the same nerve cord that runs up our spines
0:34:45 > 0:34:48and the spines of fish and other vertebrates.
0:34:48 > 0:34:52And moving along the body of the animal... Ah, well, now.
0:34:52 > 0:34:55- Here we've got the gonads.- Yes.
0:34:55 > 0:34:59Lots of them. I don't know how many pairs.
0:34:59 > 0:35:03- 20 pairs.- 20 pairs.
0:35:03 > 0:35:07So no shortage of genetic material here, then.
0:35:07 > 0:35:10- And both sides, too. - And both sides, good Lord.
0:35:10 > 0:35:14There we are, lots of gonads.
0:35:14 > 0:35:19And then, at the back end, well, you can call it a tail, can't you?
0:35:21 > 0:35:25- You can call it, yes, tail.- There's the fin. The caudal fin.- Yes.
0:35:25 > 0:35:31And in the centre, some very obvious, rather strong muscles.
0:35:31 > 0:35:36So, this is why the animal can swim and move about quite strongly
0:35:36 > 0:35:38and propel itself and wiggle around.
0:35:38 > 0:35:40- That's right.- Very good.
0:35:41 > 0:35:45'The lancelet has neither a skeleton nor much of a brain.
0:35:45 > 0:35:49'But it does have the beginnings of a backbone.
0:35:51 > 0:35:55'In 2008, its mitochondrial DNA was sequenced
0:35:55 > 0:35:59'which confirmed, for once, what my biology master told me
0:35:59 > 0:36:01'when I was still a youth.
0:36:01 > 0:36:04'It's related to the vertebrates.
0:36:04 > 0:36:07'It is like a vertebrate with almost everything subtracted.
0:36:07 > 0:36:09'A half-sketched blueprint.
0:36:10 > 0:36:13'Yet, without the ancestors of the lancelet,
0:36:13 > 0:36:19'bony fish, reptiles, amphibians, birds, mammals
0:36:19 > 0:36:22'and even us might never have come to exist.'
0:36:26 > 0:36:29So, why did the lancelets survive?
0:36:29 > 0:36:32As a filter feeder, its needs were simple,
0:36:32 > 0:36:35but then many other simple organisms did not survive the Great Dying.
0:36:35 > 0:36:37It must be something else.
0:36:37 > 0:36:42And that something else was the survival of its habitat
0:36:42 > 0:36:43in shallow seas.
0:36:43 > 0:36:47Survival of habitat buoyed it through the time of crisis.
0:36:50 > 0:36:53'The lancelet isn't the only survivor from deep time
0:36:53 > 0:36:56'that still lives in Hong Kong.
0:36:56 > 0:36:59'With Paul as my guide,
0:36:59 > 0:37:02'we set off to hunt for another elusive sea creature.
0:37:04 > 0:37:09'And our adventure begins with a monstrous warning.'
0:37:11 > 0:37:14'The sandy flats surrounding Hong Kong's New Territories
0:37:14 > 0:37:16'may be constantly shifting,
0:37:16 > 0:37:19'but they're a remarkably persistent habitat.
0:37:21 > 0:37:23'Many inter-tidal zones, like this one,
0:37:23 > 0:37:26'have hardly changed in 250 million years,
0:37:26 > 0:37:30'giving my next survivor, a shelled animal called lingula,
0:37:30 > 0:37:33'a place to hide out for a very long time.
0:37:37 > 0:37:40'Fortunately, Dr Shin's assistant Jessica is on hand
0:37:40 > 0:37:42'with a sharp eye to help.'
0:37:49 > 0:37:53Well, this is fabulous. This is, this is lingula.
0:37:53 > 0:37:58This is a real, living fossil.
0:37:58 > 0:38:02And let's see if I can get it out of the mud from its home.
0:38:02 > 0:38:03Have I managed?
0:38:04 > 0:38:08- Have I got its stalk?- Yeah, long stalk.- Well, that's great.
0:38:08 > 0:38:11That really is great. OK, let's wash him off.
0:38:13 > 0:38:15So we can have a look.
0:38:15 > 0:38:17Do you know, I'm used to seeing these things
0:38:17 > 0:38:23as fossils in rocks that are greater than 400 million years old.
0:38:30 > 0:38:32You see, it's a simple kind of shellfish
0:38:32 > 0:38:35although it's not a mollusc, not related to any kind of mollusc.
0:38:35 > 0:38:40It's got a valve at the top and it's got this funny, fleshy stalk
0:38:40 > 0:38:44hanging down below that anchors it in the mud
0:38:44 > 0:38:48and allows it to pull itself down when the tide is out.
0:38:48 > 0:38:52And when the tide comes in, it lifts itself up
0:38:52 > 0:38:54and it opens its little valves at the top
0:38:54 > 0:38:57and extracts edible particles and micro-organisms,
0:38:57 > 0:39:01using a little contraption on the inside covered in tiny hairs.
0:39:02 > 0:39:05This mode of life has allowed the animal
0:39:05 > 0:39:09to continue happily onwards through many millions of years
0:39:09 > 0:39:12while many other organisms have died out around it.
0:39:12 > 0:39:15It's a very special thing to see, indeed.
0:39:18 > 0:39:21'Many shell-bearing animals are molluscs,
0:39:21 > 0:39:24'but, in fact, lingula belongs to a distinct group of animals
0:39:24 > 0:39:26'called brachiopods,
0:39:26 > 0:39:30'most of which did not make it through the Great Dying.
0:39:32 > 0:39:35'On the outside, lingula doesn't offer us
0:39:35 > 0:39:37'very many clues as to how it survived.
0:39:43 > 0:39:47'But peering at the hinged shell, we can see the edible stalk
0:39:47 > 0:39:51'which it uses to anchor itself in place in the sand.
0:39:54 > 0:39:58'Also, the two valves that take seawater inside the animal,
0:39:58 > 0:40:02'where tiny edible particles are removed by a kind of ribbon
0:40:02 > 0:40:05'carrying cilia, called a lophophore.
0:40:08 > 0:40:11'While little hairs around the valve edges
0:40:11 > 0:40:16'prevent large, unwanted particles entering the feeding chamber,
0:40:16 > 0:40:18'any edible material is eventually passed
0:40:18 > 0:40:20'into a simple digestive system.
0:40:22 > 0:40:24'Lingula almost certainly survived
0:40:24 > 0:40:28'because it was a filter feeder whose habitat lay at the edge
0:40:28 > 0:40:30'of the toxic world.
0:40:32 > 0:40:36'It is also a simple but effective life form living in a habitat
0:40:36 > 0:40:41'that has hardly changed in hundreds of millions of years.
0:41:02 > 0:41:05'My last Hong Kong survivor is easy to find in the city's markets.
0:41:09 > 0:41:11'It litters seafloors all over the world
0:41:11 > 0:41:13'and market stalls all over China.'
0:41:19 > 0:41:24My quest for survivors has brought me to some odd places,
0:41:24 > 0:41:29perhaps none quite so strange as this fish stall in Hong Kong.
0:41:29 > 0:41:32Well, I can see all sorts of interesting things
0:41:32 > 0:41:35like dried puffer fish and I think they must be bladders,
0:41:35 > 0:41:37swim bladders of some kind.
0:41:39 > 0:41:43Oysters, perhaps smoked oysters, I'm not quite sure.
0:41:43 > 0:41:48Bottled fish, dried shrimps - they look rather appetising -
0:41:48 > 0:41:51but I can't quite see the thing I want.
0:41:52 > 0:41:55Ah, that's more like it.
0:41:57 > 0:42:00Sea cucumbers. Holothurians.
0:42:03 > 0:42:06Refugees from the Ordovician.
0:42:06 > 0:42:10Though, I must say, they don't look particularly appetising.
0:42:10 > 0:42:12And I believe these have to be soaked for four days
0:42:12 > 0:42:15before you can even begin to cook them.
0:42:15 > 0:42:19So, maybe we should find a shortcut and go to a restaurant
0:42:19 > 0:42:20and see what happens.
0:42:22 > 0:42:25'Sea cucumbers survived the Great Dying.
0:42:26 > 0:42:29'Their name suggests they are plants, but they are animals,
0:42:29 > 0:42:32'distant relatives of sea urchins and starfish.
0:42:34 > 0:42:36'An old Chinese proverb says,
0:42:36 > 0:42:40'"In China, we eat everything with legs except the table."
0:42:44 > 0:42:46'Sea cucumbers don't need legs.
0:42:48 > 0:42:50'They use collagen to twist
0:42:50 > 0:42:53'and contort their bodies into almost any shape
0:42:53 > 0:42:56'and any sheltering crevice.
0:42:56 > 0:42:58'A handy form of defence.
0:43:01 > 0:43:03'Sightless, brainless, hermaphrodites.
0:43:04 > 0:43:08'They're also scavengers, which may be the best strategy
0:43:08 > 0:43:10'for getting through an extinction event.
0:43:10 > 0:43:14'Especially one as severe as the Great Dying.
0:43:20 > 0:43:23'But my current preoccupation is rather less academic.
0:43:23 > 0:43:25'What do they taste like?'
0:43:28 > 0:43:31I'm a little bit apprehensive about eating something
0:43:31 > 0:43:36that, in the dried state, looks rather like a turd.
0:43:36 > 0:43:40But here it is, properly prepared. So I'm going to give it a taste.
0:43:40 > 0:43:42After 400 million years of existence.
0:43:44 > 0:43:47And, um, well...
0:43:49 > 0:43:51..rubbery hardly does it justice.
0:43:54 > 0:43:57'It's a good job the chef knows what he's doing.
0:43:57 > 0:44:00'Living sea cucumbers secrete a poison that can kill fish
0:44:00 > 0:44:03'and cause blindness in humans.'
0:44:03 > 0:44:05Yummy.
0:44:08 > 0:44:12'Poison is a defence sea cucumbers share with creatures
0:44:12 > 0:44:16'even further down the evolutionary tree of life.
0:44:16 > 0:44:17'The sea sponges.
0:44:20 > 0:44:23'But sea sponges don't use toxins for attack,
0:44:23 > 0:44:28'they use them to make themselves inedible.
0:44:28 > 0:44:32'But this is just one of an array of survival skills that make them
0:44:32 > 0:44:36'some of the most ancient and toughest creatures on Earth.
0:44:45 > 0:44:49'To learn from an expert, I join Dr John Hooper
0:44:49 > 0:44:52'on the way to Magnetic Island on the Barrier Reef.
0:44:54 > 0:44:56'Here, sea sponges are found in abundance,
0:44:56 > 0:45:00'and some local specimens live to be hundreds of years old.
0:45:04 > 0:45:08'John explains how their bewildering array of chemical powers
0:45:08 > 0:45:12'make them among the most versatile animals in the world.'
0:45:14 > 0:45:16I've got your favourite organism here, the sponge.
0:45:16 > 0:45:18And also, of course, one of the great survivors
0:45:18 > 0:45:22for our consideration because it's been around for,
0:45:22 > 0:45:25well, the group has been around for 600 million years.
0:45:30 > 0:45:33It's probably got all kinds of chemical defences
0:45:33 > 0:45:36- hidden away in its tissues. Is that right?- Yes, that's right.
0:45:36 > 0:45:39There's two principal reasons why sponges survived.
0:45:39 > 0:45:42One is they've got these cells called archaeocytes, they're totipotent,
0:45:42 > 0:45:46which means they can change from one function to another, and then back again.
0:45:46 > 0:45:50Very few other animals or any organisms can do that.
0:45:50 > 0:45:53So, it gives them a plasticity of growth form.
0:45:53 > 0:45:55So, if you put a sponge in a particular environment,
0:45:55 > 0:45:58it'll adapt to that environment morphologically.
0:45:58 > 0:46:01But probably the real survivorship is that, as you can see,
0:46:01 > 0:46:04this thing doesn't have arms or legs or any spikes
0:46:04 > 0:46:09or any way of removing predators or defending itself against parasites.
0:46:09 > 0:46:12So, remarkably enough, they've evolved, sponges have evolved
0:46:12 > 0:46:16an arsenal of biochemical compounds.
0:46:16 > 0:46:18What, special poisons, toxins, defences?
0:46:18 > 0:46:22You name it, they've done it. And they haven't just done it by themselves,
0:46:22 > 0:46:24some chemicals are very much sponge-produced ones.
0:46:24 > 0:46:27So, it's part of their metabolism. What do they eat?
0:46:27 > 0:46:29They break down the waste products,
0:46:29 > 0:46:32they re-use those waste products as a chemical arsenal.
0:46:32 > 0:46:34Also, these things are called sponge hotels.
0:46:34 > 0:46:36- So, they're full of bacteria.- Yeah.
0:46:36 > 0:46:39So, they have evolved defence mechanisms to harvest
0:46:39 > 0:46:43those bacteria and re-use their chemicals and the waste products
0:46:43 > 0:46:46in their own defences - it's called sequestering.
0:46:46 > 0:46:50Or they pull in the toxins from the coral reefs above them
0:46:50 > 0:46:53and they re-use those toxins and modify them.
0:46:53 > 0:46:57- So, simple they may be, but complex also, they certainly are.- Indeed.
0:47:01 > 0:47:05'Sponges can filter five times their own body weight every hour.
0:47:06 > 0:47:09'They can also grow in very oxygen-poor water,
0:47:09 > 0:47:12'which has to be one of the reasons they survived
0:47:12 > 0:47:14'the toxic seas of the Great Dying.'
0:47:17 > 0:47:20'Another is also almost certainly
0:47:20 > 0:47:23'the sponge's incredibly long life span.'
0:47:24 > 0:47:26Now, how old is that specimen?
0:47:26 > 0:47:30This specimen would be, probably, around about 100 years old.
0:47:30 > 0:47:33It takes 100 years to make something the size of a large walnut?
0:47:33 > 0:47:36One quarter of a millimetre per year growth rate.
0:47:36 > 0:47:38This one here, which is a bit larger,
0:47:38 > 0:47:40is probably a couple of hundred years old.
0:47:40 > 0:47:44And we know of specimens from the Outer Great Barrier Reef approximately this big,
0:47:44 > 0:47:46which would be thousands of years old.
0:47:46 > 0:47:50Presumably they're capable of reproducing themselves
0:47:50 > 0:47:53- during that long period? - That's right.
0:47:53 > 0:47:56So, a combination of a capacity to live an enormously long time
0:47:56 > 0:48:01and to protect themselves from all sorts of attacks
0:48:01 > 0:48:04probably adds up to a great survival strategy.
0:48:04 > 0:48:09Well, the proof's in the evidence as you see in front of you.
0:48:13 > 0:48:17'Sponges are even older than the eroded mountain tops
0:48:17 > 0:48:22'of the 500 million-year-old Remarkable Rocks.
0:48:22 > 0:48:24'But life itself is even older.
0:48:30 > 0:48:35'Sponges may appear to confuse the dividing line between vegetable
0:48:35 > 0:48:39'and animal, but my next survivor confuses the dividing line
0:48:39 > 0:48:42'between animal and mineral.
0:48:42 > 0:48:46'Tucked away on the remote western edge of Australia is Shark Bay.
0:48:48 > 0:48:52'Here, in this natural time machine, endure colonies of species
0:48:52 > 0:48:57'that have survived almost since life first began on our planet.
0:48:59 > 0:49:02'These simple-looking objects are the magicians that transform
0:49:02 > 0:49:07'the Earth into a place habitable by animals.'
0:49:10 > 0:49:12They're stromatolites.
0:49:14 > 0:49:16This one's just a few thousand years old.
0:49:16 > 0:49:19That's its kind of lumpy, crusty appearance when fresh.
0:49:19 > 0:49:27If you break it, you'll see it's full of fine layers, laminations,
0:49:27 > 0:49:33rather like filo pastry, running parallel to the edge.
0:49:33 > 0:49:40Each layer is built up by a thin film of living cells, bacteria.
0:49:44 > 0:49:48'These particular bacteria utilise carbon dioxide
0:49:48 > 0:49:52'to build up their laminations and exhale oxygen.
0:49:52 > 0:49:54'Just as plants do today.
0:49:57 > 0:50:01'This had the effect of releasing oxygen into the early atmosphere,
0:50:01 > 0:50:08'transforming it into the air that we could all breathe.
0:50:08 > 0:50:10'But it was a slow process.'
0:50:10 > 0:50:17This one is no less than 3,500 million years old.
0:50:17 > 0:50:20That's 3.5 billion years.
0:50:20 > 0:50:26Inside, a section shows the same kind of fine layering.
0:50:32 > 0:50:38It's probably the oldest organic structure anywhere on Earth.
0:50:41 > 0:50:46If it hadn't been for these tiny cells, breathing out oxygen,
0:50:46 > 0:50:49organisms like ourselves that need oxygen
0:50:49 > 0:50:51would not be able to live today.
0:50:55 > 0:50:59'Arguably, stromatolites are victims of their own success.
0:51:00 > 0:51:03'By changing the composition of the atmosphere
0:51:03 > 0:51:05'and making other forms of life possible,
0:51:05 > 0:51:09'they eventually drove themselves to the margins.
0:51:13 > 0:51:18'But persistent, marginal, amazingly inhospitable habitats
0:51:18 > 0:51:23'are where I will find the very oldest of all survivors.'
0:51:29 > 0:51:33This is a vision of a world 3.5 billion years ago.
0:51:35 > 0:51:41Here, in hot water, live countless, tiny micro-organisms -
0:51:41 > 0:51:45we call them archea and bacteria - that relish the heat.
0:51:47 > 0:51:52Under these hot springs, delicate crusts and algal mats
0:51:52 > 0:51:54and mats of bacteria combine together
0:51:54 > 0:51:58to form ancient, living communities.
0:51:59 > 0:52:03Still here, even after 3.5 billion years.
0:52:10 > 0:52:13'Yellowstone is itself a unique habitat
0:52:13 > 0:52:16'where survivors from a much later extinction event,
0:52:16 > 0:52:19'the end of the Ice Age, still thrive.
0:52:20 > 0:52:24'The bison are prepared for a sudden cold snap, but I'm not.'
0:52:25 > 0:52:28Welcome to springtime in the Northern Rockies, Richard.
0:52:28 > 0:52:32Well, you know, it's amazing to think that with all this snow
0:52:32 > 0:52:37there are still little organisms out here flourishing in extreme heat.
0:52:37 > 0:52:41Yes, it's not a question of surviving - they like it here,
0:52:41 > 0:52:42they love it here.
0:52:42 > 0:52:44You take them out of this environment,
0:52:44 > 0:52:48they either stop metabolising or they just altogether die.
0:52:48 > 0:52:49This is home sweet home.
0:52:49 > 0:52:54'With my guide, the intrepid Dr Tim McDermott, we set off
0:52:54 > 0:52:59'to seek out survivors that would not be out of place on an alien world.'
0:52:59 > 0:53:02Look at the different colours in these pools.
0:53:02 > 0:53:04Yeah, we have the yellows and the browns and the reds
0:53:04 > 0:53:07and the turquoise and the blacks.
0:53:07 > 0:53:10There's a bubbling hole, is that hydrogen sulphide coming out?
0:53:10 > 0:53:14Hydrogen sulphide and carbon dioxide, both are coming up there.
0:53:14 > 0:53:17And you can see the yellow and red round that hole there, the source,
0:53:17 > 0:53:19that's elemental sulphur.
0:53:19 > 0:53:21- So, pure sulphur.- Yes. - And then around that, a brown ring.
0:53:21 > 0:53:23Yes, that's iron.
0:53:23 > 0:53:26And what's happening is, hydrogen sulphide and the ferrous iron
0:53:26 > 0:53:29are coming to the surface and the microbes are transforming
0:53:29 > 0:53:32both of those chemicals to now form the same chemicals
0:53:32 > 0:53:33that we can now see.
0:53:33 > 0:53:37So, that's their food and the food leaves a coloured stain behind.
0:53:37 > 0:53:39Precisely, this is how they make a living.
0:53:39 > 0:53:43And then outside that, green, I see. That's from alga, yes?
0:53:43 > 0:53:46Yes, it's a lone eukaryotic organism out here in Norris Geyser Basin.
0:53:46 > 0:53:49Everything else is archea and bacteria.
0:53:49 > 0:53:52So, just in this small area we can see five different organisms,
0:53:52 > 0:53:56all leaving a different colour imprint on the ground.
0:53:56 > 0:53:58- Precisely.- Well, that's fantastic.
0:53:58 > 0:54:00And snowy.
0:54:00 > 0:54:04'These slippery walkways are certainly treacherous in the snow.
0:54:04 > 0:54:07'One slip, and I'd be in for a scalding bath.
0:54:07 > 0:54:09'But it's a curious fact
0:54:09 > 0:54:14'that something that's effectively immortal can, at the same time,
0:54:14 > 0:54:16'be so brittle and fragile.
0:54:17 > 0:54:20'Like so many of our other survivors,
0:54:20 > 0:54:24'these organisms still persist because their unique habitat does.
0:54:24 > 0:54:29'A habitat that still replicates the conditions of our planet
0:54:29 > 0:54:31'not so long after it was born.
0:54:33 > 0:54:36'From the extremophiles of Yellowstone,
0:54:36 > 0:54:41'with their unique, high-temperature home,
0:54:41 > 0:54:43'to the strange plants of Daintree...
0:54:43 > 0:54:47'and even the sea cucumbers of Hong Kong...' Hmm.
0:54:50 > 0:54:53'..All animals and plants are adapted to their own habitat.
0:54:53 > 0:54:55'If it persists,
0:54:55 > 0:54:59'then they will usually survive, along with their home.'
0:55:01 > 0:55:03We're used to thinking, perhaps,
0:55:03 > 0:55:06of those really richly biodiverse places,
0:55:06 > 0:55:10like rainforests and coral reefs, as needing special protection.
0:55:12 > 0:55:16But other places, where species that have endured for millions
0:55:16 > 0:55:20and millions of years still live on, are, perhaps, even more valuable
0:55:20 > 0:55:24as windows seeing back deep into geological time,
0:55:24 > 0:55:28telling us about our own history and the history of life.
0:55:28 > 0:55:33I call these places time havens and I think they're worth protecting.
0:55:33 > 0:55:36Well, Kevin, what survivors have we got here?
0:55:36 > 0:55:40'Unglamorous these time havens and the species that live in them may be,
0:55:40 > 0:55:46'but because of human interference, many are now under greater threat
0:55:46 > 0:55:49'than at any time since the Great Dying.'
0:55:49 > 0:55:53Well, that's a true, living fossil for you.
0:55:53 > 0:55:55'Luckily, there are those amongst us
0:55:55 > 0:55:59'determined to help our greatest survivors survive.'
0:55:59 > 0:56:03- The second species that we have. - Oh, what a giant.
0:56:03 > 0:56:07This is the Chinese horseshoe crab. Be careful.
0:56:07 > 0:56:10- This is also a lady.- Fantastic.
0:56:10 > 0:56:13And, oh, look, the spikes are almost getting me that time.
0:56:15 > 0:56:18'Kevin Laurie is a retired Hong Kong policeman
0:56:18 > 0:56:21'who shares my passion for horseshoe crabs.
0:56:21 > 0:56:24'They were once common in Hong Kong's waters, but pollution,
0:56:24 > 0:56:28'fishing and industrialisation have taken a heavy toll.'
0:56:28 > 0:56:32My goodness. So, they take a long time to grow.
0:56:32 > 0:56:34It's a very slow generation time.
0:56:34 > 0:56:38'Kevin has joined Dr Paul Shin in trying to repopulate
0:56:38 > 0:56:41'the dwindling numbers of horseshoe crabs
0:56:41 > 0:56:43'found around the New Territories.
0:56:45 > 0:56:48'Bred in captivity, when they're a year old,
0:56:48 > 0:56:53'these tiny horseshoe crabs are released back into the wild.'
0:56:57 > 0:57:00OK, these are the babies from the breeding programme.
0:57:00 > 0:57:02I took them out this morning. These are yearlings.
0:57:02 > 0:57:06Yearlings, sweet little creatures.
0:57:06 > 0:57:09And they'll go and feed on the seagrass
0:57:09 > 0:57:11and then mature further out to sea
0:57:11 > 0:57:14and then come back and breed in 16 years' time.
0:57:16 > 0:57:2116 years to become adults. 16 or 17 months all on this seagrass bit.
0:57:23 > 0:57:26Well, let's put some more of these little creatures
0:57:26 > 0:57:29back into the wild and help them to grow to adults.
0:57:32 > 0:57:36Just lay them on the mudflats - and there's one moving off,
0:57:36 > 0:57:37quite quickly.
0:57:37 > 0:57:40They're beginning to bury themselves already.
0:57:40 > 0:57:44Well, they may not do a great deal, these horseshoe crabs,
0:57:44 > 0:57:46but what they do, they do extremely well.
0:57:46 > 0:57:49Maybe that's one of the secrets of their survival.
0:57:51 > 0:57:55'As I watched the next generation of crabs hide itself away in the mud
0:57:55 > 0:58:00'of this time haven, I'm struck by a final poignant thought.
0:58:02 > 0:58:04'Had the Great Dying never happened,
0:58:04 > 0:58:08'life as we know it might be profoundly different,
0:58:08 > 0:58:12'and human beings might never have evolved in the first place.
0:58:12 > 0:58:15'So it is no exaggeration to say,
0:58:15 > 0:58:20'we are all the sons and daughters of disaster.'
0:58:23 > 0:58:26'In the next episode, I go in search of survivors
0:58:26 > 0:58:30'from the most dramatic of all extinction events.
0:58:30 > 0:58:34'The asteroid impact that wiped out the dinosaurs.'
0:58:41 > 0:58:44Subtitles by Red Bee Media Ltd
0:58:44 > 0:58:48E-mail subtitling@bbc.co.uk