WEBVTT 00:00:14.120 --> 00:00:15.120 Nightfall… 00:00:19.240 --> 00:00:22.880 reveals our planet's connection to the universe. 00:00:28.160 --> 00:00:29.560 A shooting star. 00:00:31.200 --> 00:00:34.480 Ancient rock from the depths of space… 00:00:38.680 --> 00:00:39.880 falling to Earth. 00:00:50.320 --> 00:00:54.880 Inside it are the chemical elements that built our universe. 00:01:10.480 --> 00:01:12.160 For countless generations, 00:01:13.000 --> 00:01:16.160 sea turtles have roamed the oceans, 00:01:16.760 --> 00:01:20.480 gathering cosmic elements in the food they eat. 00:01:24.160 --> 00:01:27.720 And as they've done for hundreds of millions of years… 00:01:33.880 --> 00:01:35.560 every new generation 00:01:37.520 --> 00:01:40.360 recycles this same stardust… 00:01:43.320 --> 00:01:45.200 to produce the next. 00:01:53.800 --> 00:01:55.400 Born in The Big Bang… 00:01:56.840 --> 00:01:59.400 …and forged in the hearts of stars… 00:02:01.640 --> 00:02:05.600 …90 chemical elements have created everything. 00:02:08.120 --> 00:02:10.680 Endlessly recycled and reconfigured 00:02:11.680 --> 00:02:15.160 throughout the entire history of the universe. 00:02:18.240 --> 00:02:19.480 And now… 00:02:21.640 --> 00:02:23.440 using the same elements, 00:02:24.760 --> 00:02:27.400 each new turtle begins a life cycle… 00:02:33.960 --> 00:02:37.600 …that mirrors the lives of the stars. 00:03:18.400 --> 00:03:20.960 On Australia's Great Barrier Reef… 00:03:28.680 --> 00:03:31.120 …something magical has happened. 00:03:37.880 --> 00:03:40.280 After 50 days beneath the sand, 00:03:41.480 --> 00:03:46.880 chemical elements from across the cosmos have created life. 00:03:49.280 --> 00:03:52.480 Combining to form the next generation 00:03:53.480 --> 00:03:54.960 of green sea turtles. 00:04:18.400 --> 00:04:22.400 The eggs have now exhausted their supply of life-giving elements. 00:04:39.760 --> 00:04:45.160 And today, the baby turtles will take their first taste of air. 00:04:59.080 --> 00:05:03.000 And as her brothers and sisters scramble to make it to the water… 00:05:08.600 --> 00:05:09.800 a little female… 00:05:12.560 --> 00:05:14.400 is last to be born. 00:05:20.120 --> 00:05:22.160 In order to grow to adulthood, 00:05:23.880 --> 00:05:27.720 she will need to harvest chemical elements from across the ocean. 00:05:36.800 --> 00:05:38.400 It's a dangerous journey… 00:05:41.120 --> 00:05:43.280 …with treachery at every turn. 00:05:50.400 --> 00:05:51.880 But for the baby turtles, 00:05:53.200 --> 00:05:56.360 the call of the ocean is irresistible. 00:06:09.840 --> 00:06:11.200 From a nest of 100, 00:06:12.320 --> 00:06:14.880 sometimes only one will survive. 00:06:18.680 --> 00:06:20.840 Sometimes none. 00:07:13.560 --> 00:07:15.080 But despite the risk, 00:07:17.240 --> 00:07:19.040 the little female knows 00:07:19.560 --> 00:07:21.880 she must make it to the water. 00:07:59.880 --> 00:08:01.320 She spots an opening… 00:08:04.680 --> 00:08:05.920 and takes her chance. 00:08:20.880 --> 00:08:21.720 Today… 00:08:24.400 --> 00:08:25.720 she's a lucky one. 00:08:29.080 --> 00:08:34.400 The hatchling won't stop swimming until she has left the reef far behind. 00:08:47.120 --> 00:08:51.520 Safely past the predators that gather in the shallow coastal waters, 00:08:52.720 --> 00:08:55.920 she'll disappear into the great void of the open ocean… 00:09:03.200 --> 00:09:07.600 to spend her childhood feeding on atoms. 00:09:14.240 --> 00:09:20.920 Atoms whose origins go back through the entire life of the cosmos. 00:09:26.640 --> 00:09:30.040 To the time our universe 00:09:30.640 --> 00:09:32.440 was in its infancy. 00:09:48.000 --> 00:09:53.080 Expanding from nothing to everything in an instant. 00:09:56.280 --> 00:09:59.800 Our universe was born in The Big Bang. 00:10:07.400 --> 00:10:08.280 At first, 00:10:09.040 --> 00:10:11.800 it was nothing but a hot, dense fog. 00:10:19.080 --> 00:10:21.480 But as it continued to expand… 00:10:24.360 --> 00:10:26.000 the fog began to cool. 00:10:29.400 --> 00:10:32.040 And on the tiniest scale imaginable… 00:10:33.600 --> 00:10:35.960 …something astounding began to occur. 00:10:42.000 --> 00:10:45.400 The first atoms condensed out of the fog. 00:10:50.120 --> 00:10:52.400 Atoms of hydrogen. 00:10:56.040 --> 00:10:59.600 The very first element in the universe. 00:11:06.640 --> 00:11:07.800 And in the ocean, 00:11:08.680 --> 00:11:11.920 juvenile turtles are hunting it down. 00:11:15.160 --> 00:11:17.480 As they emerge from the blue 00:11:17.560 --> 00:11:20.120 to forage in the shallow waters of the reef. 00:11:24.920 --> 00:11:26.560 This is Stella. 00:11:27.760 --> 00:11:30.640 One of the lucky ones that made it off the beach 00:11:31.280 --> 00:11:32.520 and into the ocean. 00:11:41.480 --> 00:11:44.680 She's already more than 2,000 times her hatching weight 00:11:45.840 --> 00:11:46.880 and growing fast. 00:11:51.840 --> 00:11:55.360 Feeding on creatures she's found drifting in the open ocean, 00:11:56.840 --> 00:11:59.880 she's harvested one element more than any other. 00:12:08.640 --> 00:12:09.480 Hydrogen. 00:12:12.560 --> 00:12:16.800 It makes up more than half of all the atoms in the food she eats. 00:12:20.800 --> 00:12:24.480 And is the most abundant element in all living things. 00:12:28.600 --> 00:12:29.680 From fish 00:12:30.960 --> 00:12:32.200 to invertebrates. 00:12:38.960 --> 00:12:41.320 Anemones and coral. 00:12:54.440 --> 00:12:58.560 Hydrogen atoms formed at the dawn of the universe 00:12:59.520 --> 00:13:03.200 have been passed on from star to planet, 00:13:04.320 --> 00:13:05.920 planet to animal… 00:13:08.320 --> 00:13:11.280 and from prey to predator. 00:13:22.080 --> 00:13:23.480 Which means, for Stella, 00:13:24.280 --> 00:13:27.000 the waters around the reef are full of danger. 00:13:30.880 --> 00:13:33.920 Tiger sharks, hungry for the same atoms, 00:13:34.000 --> 00:13:37.000 hunt sea turtles throughout their adult lives. 00:13:45.280 --> 00:13:48.560 Stella's main defense is her trusty armor. 00:13:52.280 --> 00:13:55.280 Its bone toughened with calcium and phosphorus. 00:14:02.320 --> 00:14:05.320 Elements that date back to another pivotal moment… 00:14:09.400 --> 00:14:11.280 in the life of our universe. 00:14:21.920 --> 00:14:25.680 For the first 300 million years after The Big Bang… 00:14:28.080 --> 00:14:31.000 there are no planets and no stars. 00:14:34.080 --> 00:14:36.600 The dark ages of the universe. 00:14:42.360 --> 00:14:44.120 Concealed in the gloom, 00:14:44.640 --> 00:14:48.600 vast tendrils of hydrogen gas crisscross the cosmos. 00:14:53.280 --> 00:14:55.560 And then, incredibly, 00:14:56.200 --> 00:14:58.680 as they were drawn together by gravity… 00:15:02.400 --> 00:15:04.520 …the first stars were born. 00:15:11.120 --> 00:15:13.000 This is the cosmic dawn. 00:15:16.720 --> 00:15:20.880 The moment the lights came on. 00:15:28.000 --> 00:15:30.680 And deep within those first stars… 00:15:34.880 --> 00:15:37.080 a remarkable process began. 00:15:42.800 --> 00:15:46.080 Temperatures and pressures were so extreme… 00:15:48.080 --> 00:15:50.360 …that new elements were created. 00:15:52.520 --> 00:15:56.400 Atoms of hydrogen were forced together to make helium. 00:15:58.800 --> 00:16:01.880 As they fused, energy was released. 00:16:04.520 --> 00:16:09.200 Creating a chain reaction that produced increasingly heavier elements. 00:16:12.320 --> 00:16:15.640 Including those essential for life. 00:16:17.640 --> 00:16:21.360 Three helium atoms combined to make carbon. 00:16:26.800 --> 00:16:29.480 The element on which all life is based. 00:16:31.760 --> 00:16:34.560 Carbon and helium made oxygen. 00:16:36.120 --> 00:16:37.400 The air we breathe. 00:16:39.680 --> 00:16:42.880 Oxygen atoms combined to make phosphorus. 00:16:44.920 --> 00:16:47.160 Then silicon and calcium. 00:16:50.200 --> 00:16:52.800 The elements that make up every living thing 00:16:54.320 --> 00:16:58.800 were created in the hearts of the very first stars. 00:17:31.000 --> 00:17:31.880 For Stella, 00:17:33.160 --> 00:17:35.040 some elements are so important… 00:17:38.600 --> 00:17:41.080 …she'll travel great distances to find them. 00:17:51.600 --> 00:17:56.000 The warm, shallow waters between Australia and Papua New Guinea 00:17:57.360 --> 00:17:59.800 are a paradise of vibrant seagrass. 00:18:04.200 --> 00:18:06.680 The prairies of the ocean. 00:18:16.120 --> 00:18:21.960 Stella has traveled all the way here to access their magic ingredients. 00:18:32.560 --> 00:18:34.000 As it grows, 00:18:34.080 --> 00:18:37.200 seagrass absorbs elements from outer space 00:18:37.920 --> 00:18:40.680 that have found their way to the ocean floor. 00:18:43.880 --> 00:18:48.040 Burgeoning fronds rich in calcium and phosphorus 00:18:49.760 --> 00:18:53.280 provide Stella with precisely the minerals she needs 00:18:55.080 --> 00:18:58.320 to build and sustain her protective shell. 00:19:01.880 --> 00:19:06.000 Hardening her armor for the trials ahead. 00:19:14.400 --> 00:19:16.960 Stella will spend her adolescent years 00:19:17.680 --> 00:19:19.200 searching the ocean 00:19:20.920 --> 00:19:24.240 for atoms born in the stars. 00:19:33.240 --> 00:19:35.080 Her journey toward maturity… 00:19:37.320 --> 00:19:40.800 paralleled in the story of our universe. 00:19:45.680 --> 00:19:48.920 Because three billion years after The Big Bang… 00:19:53.880 --> 00:19:56.680 …the universe was also coming of age. 00:20:02.640 --> 00:20:08.440 It was entering an incredibly active phase of star formation. 00:20:12.200 --> 00:20:13.240 As they grew, 00:20:13.960 --> 00:20:17.280 stars were pulled together into vast galaxies. 00:20:20.080 --> 00:20:21.800 Like our Milky Way. 00:20:25.000 --> 00:20:26.880 And within those galaxies, 00:20:28.160 --> 00:20:30.840 the chemical elements each star produced… 00:20:34.520 --> 00:20:40.960 …were transformed into planets and moons. 00:20:49.920 --> 00:20:51.480 After billions of years, 00:20:53.320 --> 00:20:58.880 chemical elements have matured into the Earth we know today. 00:21:23.080 --> 00:21:25.800 Stella is now fully grown herself. 00:21:29.880 --> 00:21:31.240 Over a meter long, 00:21:32.280 --> 00:21:35.600 she has a thick shell covered in green algae. 00:21:39.240 --> 00:21:42.400 Ideal camouflage for cruising coral reefs. 00:21:46.600 --> 00:21:49.120 She is now at one with the ocean. 00:21:55.800 --> 00:21:57.440 Atoms from the stars 00:21:59.320 --> 00:22:02.600 perfectly adapted to life at sea. 00:22:11.000 --> 00:22:13.120 Just one example of life on Earth… 00:22:15.280 --> 00:22:18.320 exquisitely shaped from the cosmos. 00:22:35.560 --> 00:22:39.000 Stella is now ready for the next stage of her life. 00:22:43.680 --> 00:22:47.000 Because she's about to become a mother herself. 00:22:50.200 --> 00:22:51.320 Inside her body… 00:22:53.960 --> 00:22:56.480 she's carrying a clutch of 100 eggs. 00:22:58.280 --> 00:23:01.080 The first of many she'll have over her lifetime. 00:23:03.680 --> 00:23:07.880 Her own precious cargo of stardust. 00:23:15.760 --> 00:23:17.120 All across the reef, 00:23:18.360 --> 00:23:20.720 atoms are being assembled into new life. 00:23:25.480 --> 00:23:30.160 Creating one of the richest ecosystems on Earth. 00:23:35.920 --> 00:23:38.000 But our planet… 00:23:41.320 --> 00:23:42.400 …is an outlier. 00:23:44.960 --> 00:23:47.120 In the rest of the solar system, 00:23:47.200 --> 00:23:49.160 the very same elements 00:23:49.240 --> 00:23:54.000 have created worlds far less suited to life. 00:23:59.920 --> 00:24:01.320 Closest to the sun, 00:24:02.080 --> 00:24:05.000 Mercury is a planet rich in carbon. 00:24:07.880 --> 00:24:09.680 But rather than creating life, 00:24:11.560 --> 00:24:13.800 the carbon is baked into its crust. 00:24:16.160 --> 00:24:19.920 On a world scorched by starlight. 00:24:22.520 --> 00:24:26.440 While in the farthest reaches of the solar system, 00:24:26.520 --> 00:24:28.560 Neptune's freezing temperatures 00:24:29.480 --> 00:24:33.520 cause carbon and hydrogen to form clouds of methane. 00:24:36.680 --> 00:24:40.880 The suffocating gas that gives it its brilliant blue. 00:24:46.640 --> 00:24:47.960 And even on Mars, 00:24:49.160 --> 00:24:51.960 a planet with all the same ingredients as Earth… 00:24:54.320 --> 00:24:56.880 the lack of an oxygen-rich atmosphere 00:24:57.520 --> 00:25:00.880 means complex life couldn't survive here. 00:25:07.800 --> 00:25:12.080 Only on Earth are conditions just right. 00:25:18.320 --> 00:25:19.320 But even here, 00:25:20.120 --> 00:25:22.280 competition for elements is fierce. 00:25:24.200 --> 00:25:25.040 And danger… 00:25:27.560 --> 00:25:29.040 …is never far away. 00:25:44.880 --> 00:25:48.400 Luckily, Stella has become an expert at hide-and-seek. 00:26:29.920 --> 00:26:31.400 Safe for now… 00:26:34.320 --> 00:26:37.320 Stella faces the biggest challenge of her life. 00:26:39.520 --> 00:26:42.280 To return to the Great Barrier Reef 00:26:43.920 --> 00:26:45.600 and the island of her birth… 00:26:49.480 --> 00:26:51.880 to lay her own eggs in the sand. 00:26:58.880 --> 00:27:01.440 But a lifetime spent wandering the ocean 00:27:02.200 --> 00:27:05.600 means she's now 2,000 kilometers away. 00:27:09.840 --> 00:27:11.520 How Stella navigates home 00:27:12.160 --> 00:27:14.760 is one of the wonders of the natural world. 00:27:21.400 --> 00:27:22.760 Deep within the Earth, 00:27:23.600 --> 00:27:26.600 our planet's core generates a magnetic field… 00:27:28.840 --> 00:27:33.880 which gives every place on its surface a unique magnetic signature. 00:27:37.560 --> 00:27:39.120 When she hatched, 00:27:39.200 --> 00:27:43.520 her island's signature was imprinted in Stella's brain. 00:27:46.200 --> 00:27:48.200 And to find her way back, 00:27:48.280 --> 00:27:51.600 she'll rely on yet another chemical element. 00:27:53.760 --> 00:27:56.880 One that connects her to the planet's core. 00:28:00.400 --> 00:28:05.080 An element that's only created when stars die. 00:28:10.680 --> 00:28:12.720 In a nearby part of the galaxy, 00:28:13.720 --> 00:28:15.680 two and a half million years ago, 00:28:16.720 --> 00:28:20.520 a dramatic change took place in the core of a giant star. 00:28:25.280 --> 00:28:29.360 For all its life, it had been powered by nuclear fusion. 00:28:35.880 --> 00:28:37.200 The energy released… 00:28:39.040 --> 00:28:41.440 …creating heavier and heavier elements. 00:28:45.200 --> 00:28:48.120 Until the core became so hot, 00:28:48.640 --> 00:28:49.880 it started creating… 00:28:51.640 --> 00:28:52.480 …iron. 00:28:55.360 --> 00:28:58.200 Which caused a fundamental change to take place. 00:29:03.080 --> 00:29:06.360 Because making iron doesn't release energy. 00:29:07.880 --> 00:29:09.160 It consumes it. 00:29:15.880 --> 00:29:18.360 As more and more of the metal was produced, 00:29:19.240 --> 00:29:22.760 it spread through the core like a disease. 00:29:27.160 --> 00:29:29.160 Feeding off the star's heat. 00:29:33.880 --> 00:29:34.880 Throttling it. 00:29:46.280 --> 00:29:48.560 With no heat source to hold it up. 00:29:52.840 --> 00:29:54.400 From this moment onward… 00:29:57.480 --> 00:29:59.680 …the star was doomed. 00:30:11.600 --> 00:30:16.200 The resulting explosion shone with the brightness of 10 billion suns. 00:30:22.000 --> 00:30:27.080 A supernova which propelled iron-rich dust across the galaxy. 00:30:35.120 --> 00:30:38.120 All the way to our planet. 00:30:43.160 --> 00:30:44.280 And even now, 00:30:45.280 --> 00:30:50.280 100 tons of stardust enters Earth's atmosphere every day. 00:30:53.080 --> 00:30:56.800 Some left over from the formation of the solar system. 00:31:00.600 --> 00:31:04.480 Some blown here from distant supernovas. 00:31:08.400 --> 00:31:13.600 A direct link between our planet and the stars. 00:31:19.680 --> 00:31:21.960 And it's the iron in this dust 00:31:22.520 --> 00:31:25.400 that allows Stella to find her way. 00:31:33.520 --> 00:31:35.200 Because deep in her brain… 00:31:38.280 --> 00:31:43.600 …specialized cells are thought to contain crystals of magnetite. 00:31:44.520 --> 00:31:48.760 An iron-rich mineral that aligns itself to the Earth's magnetic field. 00:31:52.760 --> 00:31:53.680 A compass, 00:31:55.560 --> 00:31:57.680 pointing her in the right direction. 00:32:05.440 --> 00:32:11.680 Allowing Stella to find the unique magnetic fingerprint of home. 00:32:19.480 --> 00:32:22.680 And so an element forged in a supernova… 00:32:30.360 --> 00:32:34.280 …will now guide her across kilometers of featureless ocean. 00:32:48.600 --> 00:32:49.920 Back to the island… 00:32:53.800 --> 00:32:55.480 on which she was born. 00:33:08.120 --> 00:33:12.040 But there are other creatures with magnetic homing abilities. 00:33:14.680 --> 00:33:16.480 The tiger sharks have it too. 00:33:19.600 --> 00:33:22.280 And it's leading them back to the same island. 00:33:26.560 --> 00:33:28.920 Because for a few months every year, 00:33:29.000 --> 00:33:32.600 thousands of female turtles come here to lay their eggs. 00:33:34.600 --> 00:33:37.880 It's the largest gathering of green sea turtles 00:33:37.960 --> 00:33:39.960 anywhere on the planet. 00:33:45.600 --> 00:33:47.320 And as they come to shore, 00:33:49.080 --> 00:33:50.320 the feeding begins. 00:34:03.800 --> 00:34:06.160 Stella must wait for the right moment… 00:34:08.840 --> 00:34:10.040 to find an opening… 00:34:12.160 --> 00:34:14.080 and avoid the onslaught. 00:34:32.080 --> 00:34:33.800 When the danger has passed… 00:34:37.440 --> 00:34:39.080 she finally swims ashore. 00:34:52.280 --> 00:34:53.880 After an epic journey… 00:34:57.080 --> 00:34:59.240 Stella emerges onto the sand 00:35:00.840 --> 00:35:03.320 she last touched as a hatchling. 00:35:28.040 --> 00:35:30.920 The elements she spent a lifetime collecting… 00:35:36.600 --> 00:35:39.160 are now safely delivered into the sand. 00:35:45.240 --> 00:35:46.960 Stella's mission is complete, 00:35:47.520 --> 00:35:49.240 and she returns to the ocean… 00:35:52.880 --> 00:35:56.600 to begin gathering stardust once more. 00:36:00.480 --> 00:36:01.800 The cycle of her life 00:36:03.640 --> 00:36:06.520 mirroring the grandest cycle of all. 00:36:08.440 --> 00:36:11.920 The lives and deaths of the stars. 00:36:22.480 --> 00:36:25.600 Because far away across the galaxy, 00:36:27.000 --> 00:36:29.680 the ashes of countless supernovas 00:36:29.760 --> 00:36:34.480 have come together to form a giant nebula. 00:36:41.280 --> 00:36:44.480 A cloud of stardust tens of light-years across. 00:36:48.120 --> 00:36:52.600 And buried within it are places where the next generation of stars 00:36:53.840 --> 00:36:55.280 are beginning to form. 00:37:06.800 --> 00:37:08.400 Called proplyds. 00:37:10.400 --> 00:37:12.880 They're like vast cosmic eggs. 00:37:15.000 --> 00:37:17.680 Each one bigger than our solar system. 00:37:23.720 --> 00:37:26.640 Inside their shells of ionized gas, 00:37:28.560 --> 00:37:31.480 the force of gravity is pulling stardust together. 00:37:38.880 --> 00:37:42.400 And the stardust inside Stella's eggs… 00:37:45.440 --> 00:37:47.560 is also beginning to take shape. 00:37:56.200 --> 00:38:01.800 As the elements she collected are being transformed… 00:38:08.280 --> 00:38:11.800 into something that's starting to resemble a tiny creature. 00:38:24.280 --> 00:38:25.640 And within the proplyd… 00:38:27.840 --> 00:38:30.240 gases like hydrogen and helium… 00:38:33.120 --> 00:38:35.680 …are feeding an embryonic star. 00:38:44.880 --> 00:38:46.680 And what was once an embryo… 00:38:49.080 --> 00:38:51.080 is now a tiny turtle… 00:38:55.200 --> 00:38:58.880 with shell, flippers, and beak. 00:39:02.880 --> 00:39:04.680 Elements reimagined… 00:39:08.080 --> 00:39:10.280 for a life at sea. 00:39:15.160 --> 00:39:16.120 In the proplyd, 00:39:17.000 --> 00:39:20.200 the new star's development is also nearing completion. 00:39:21.480 --> 00:39:24.800 Reborn from the ashes of the previous generation, 00:39:26.120 --> 00:39:30.000 its light now reveals a family of growing planets in orbit. 00:39:34.200 --> 00:39:35.320 New worlds. 00:39:36.240 --> 00:39:40.280 But perhaps, new possibilities for life. 00:39:48.280 --> 00:39:49.920 And beneath the sand, 00:39:51.240 --> 00:39:52.760 the same stardust, 00:39:54.080 --> 00:39:58.800 passed down through countless generations of stars and turtles… 00:40:00.880 --> 00:40:03.200 will start yet another journey. 00:40:08.160 --> 00:40:09.560 Each new life 00:40:11.080 --> 00:40:15.400 directly connected to the origin of the universe. 00:40:20.840 --> 00:40:26.400 Each new story beginning at the end of the last. 00:40:34.880 --> 00:40:38.880 And so, the story of our universe continues… 00:40:40.760 --> 00:40:43.000 …with Earth's most precious resource… 00:40:46.280 --> 00:40:47.120 …water. 00:40:48.920 --> 00:40:52.800 And a family of elephants on a dangerous mission to find it. 00:40:57.000 --> 00:40:59.360 Their journey every bit as extraordinary… 00:41:01.680 --> 00:41:06.440 …as water's journey across the vastness of space to our planet. 00:41:10.640 --> 00:41:13.840 But why is Earth the only world in the solar system 00:41:14.840 --> 00:41:17.240 whose surface is covered with liquid water? 00:41:18.600 --> 00:41:21.960 And why is it so essential for life?