(dramatic music) - [Narrator] In the fiery beginning of our young solar system, world's are born. And obliterated. (dramatic music) Gas giants stir chaos and a young Sun vents its rage.
(dramatic music) How did Earth survive against all odds? (dramatic music) Gazing down from space we marvel at Earth's bountiful oceans, its continents, and life giving atmosphere. We ask how did our planet begin?
How did it come support life? And life to support Earth? (intense music) The story of Earth starts within a giant spiral galaxy, the Milky Way.
At 100,000 light years across the galaxy is a cauldron of swirling dust clouds and glowing gas. (intense music) This simulated view shows a 50 million year span, a cosmological blink of an eye. (intense music) In that time millions of stars die in powerful explosions called supernovae, shown here as flashes of light.
(intense music) They seed the cosmos with the stuff of planets. Carbon, silicon, iron and more. (intense music) One explosion has packed enough punch to send a nearby cloud of stardust into collapse.
(intense music) Huge volumes of dust and gas stream into its core. (intense music) This cloud is about as cold the universe gets. But the tighter it's packed the more it heats up.
(intense music) A storm erupts at its center, a vast raging hurricane of dust, gas and ice crystals. (intense music) In its eye temperatures soar, a star ignites and our Sun is born. (intense music) The Sun is being fed by a slowly spinning disk.
The cradle of our solar system. Within the disk planets take shape in a long violent process. It starts with dust gathering into sand-like grains.
(intense music) They form pebble sized objects within clouds of loose gravel. (intense music) Over millions of years gravity draws them together to form rocks, ice balls and boulders. (intense music) These objects coalesce into miniature planets, or planetesimals.
One such body, the primordial Earth, is growing steadily, but it's fate hangs in the balance. (intense music) We once thought that planet formation followed a predictable pattern. Our planetary neighbors bear this out with their nearly circular orbits.
And the neat division between gaseous outer planets. Jupiter. Saturn.
Uranus. And Neptune. And rocky inner planets.
Mercury. Venus. Earth.
And Mars. This division originates soon after a star ignites. The young Sun produces hot winds that drive lighter hydrogen gas to the outer part of the disk.
Beyond a point called the ice line large gas planets grow quickly by sweeping up gas pushed out by the Sun. The dusty inner region, devoid of gas and ice, is where rocky worlds like Earth form. This is not necessarily how most solar systems end up.
(intense music) A new generation planet finding telescopes has found that gas planets the size of our Neptune commonly patrol the inner zones. (intense music) Jupiter sized giants have been found orbiting so close to the star that hot stellar winds are stripping them of gas. (intense music) Then there's a class of large rocky planets called Super Earths.
How did those planets get there? Why did our own inner planet stay so small? Much of what we know about the formation of our solar system comes from asteroids that haven't changed since they formed almost 5 billion years ago.
Most are so small that they simply burn up in our atmosphere. (intense music) A few larger ones survive the fall. Scientists have been able to dig these planetary shards by measuring molecular variations called isotopes, in particular metals.
They appear to come from two distinct asteroid populations that formed in the inner and the outer solar system. Something must have driven a wedge between these two regions, preventing the objects from mixing. (intense music) If this great divider was the young Jupiter it had to have grown quickly.
It would have cut off the flow of matter into the inner solar system, staling the formation of large rocky planets, or Super Earths. Jupiter would then play a central role in one of the most impactful chapters in the history of our solar system. (intense music) Scientists have used super computers to model Jupiter's rise by simulating the interaction of dust, gas, ice and boulders in the early solar system Each flash marks a collision.
Each ring tracks the orbit of a would be planet. (intense music) Giant Jupiter forms on the periphery, its orbit shown in blue. (intense music) As it grows Jupiter succumbs to the gravitational pull of the inner solar system.
It begins to spiral toward the Sun. (intense music) Scientists call Jupiter's big move the grand tack, named for the term a sailboat takes into the wind. (intense music) Along the way Jupiter plows through clouds of cosmic debris.
(intense music) What it doesn't swallow it flings out of the solar system. (intense music) The closer Jupiter draws toward the Sun the more cosmic clutter it clears away. (intense music) The simulation tracks Jupiter all the way into the orbit of present day Mars.
(intense music) Jupiter's grand tack has further reduced the mass of the inner solar system. Now any planet's that form there will be relatively small. (intense music) In time another giant planet, Saturn, grows large enough to pull Jupiter back out.
(intense music) Earth, at that time, would have been an embryo of the planet it would one day become. (intense music) With Jupiter's departure, Earth and a few dozen hungry competitors are free to scour the inner solar system for scraps. (intense music) Which ones will survive depends on the luck of the cosmic draw.
(intense music) Over the 50 million years since Jupiter departed the inner solar system the roller derby of planets goes wild. (intense music) As the remaining planets tug on one another their orbits destabilize. Collisions between them are inevitable.
(intense music) What's left is a handful of would be worlds, including the planets we know today, and at least one other. (intense music) Its existence was deduced in the wake of one of the most celebrated milestones in the history of human exploration. (dramatic music) On July the 16th, 1969 Apollo 11 blasts off.
(dramatic music) In 13 launches the US heavy lift launch vehicle, the mighty Saturn 5 rocket, never failed to safely deliver its payload. (dramatic music) Six times in the four years from 1969 to 1972 Apollo space craft drifted down over a pocked lunar surface. (soft music) 12 astronauts climbed out to experience the Moon up close.
They set up experiments. Made measurements. And collected rocks as they walked, or drove across the alien terrain.
(intense music) The world cheered as the astronauts returned to Earth. Their exploits symbolized a spirit of optimism. A bright ray of hope in a troubled time.
They were the first, and so far the last, humans to travel beyond Earth and land another world. (soft music) Few suspected at the time that the rocks they brought back to Earth would spur a chain of major discoveries about the Moon and Earth. Back in NASA labs scientists found that rocks from the Moon have much in common with those from Earth.
In particular they share forms of oxygen regarded as blood types for solar system bodies. (soft music) The two bodies share a common and violent history. That history is written across the lunar surface.
The Moon is pocked with large old craters, surrounded by concentric rings. You can see them in this image of the Mare Orientale captured recently by NASA's lunar reconnaissance orbiter. The rings suggest that a giant impacter came down on a roiling, red hot liquid surface, sending ripples outward.
(soft music) The astronauts encountered relatively light rocks strewn about the landing sites, probably forced to the surface by heavier material as it sunk down into the magma. They also picked up rocks eventually nicknamed creep, for the constituents potassium, rare Earth elements and phosphorus. These rocks of a type called Anorthosite are a product of a molten surface.
What had turned the Moon into an ocean of molten rock? And what is the connection to Earth? The most widely accepted theory takes us back to a time four and a half billion years ago.
(intense music) At this time Earth may harbor volcanoes on its surface, with a thin toxic atmosphere. (intense music) Our planet has sofar withstood the on slot of planet formation. It now awaits the test of its life.
(intense music) Another planet, about half its size, is closing in. This is Theia, a world have might have been. Instead its journey ends here as it bears down on Earth.
(intense music) Imagine the view from Earth as the ultimate threat looms large on the horizon. (intense music) Theia rocks Earth to the core. (intense music) The impact sheers away a third of our planet but instead of destroying Earth, Theia becomes part of it.
A computer simulation captures the first 24 hours. Debris unleashed by the collision envelopes Earth in a dense atmosphere of vaporized rock. The cloud coalesces into a ring, a belt of molten rubble.
(intense music) Much of the orbiting debris rains back to the surface, but within a century what's left gathers into a single wondrous body, Earth's companion, the Moon. (thoughtful music) After the impact our planet is left spinning rapidly, on a slightly tilted axis. (thoughtful music) The Moon orbits much closer to Earth than it does today, for its surface our world would have filled the sky.
(thoughtful music) As the Moon gradually slips into a more distant orbit its exerts a drag on Earth, that slows our planet's spin, and steadies its tilt. (thoughtful music) The Moon serves as a reminder of the cataclysm that almost spelled the end of our planet. (thoughtful music) But from here on it would be a welcome constant, a source of stability, and ultimately, beauty.
(thoughtful music) But the violence was by no means over. Unlike Earth, where erosion and geological events have erased all traces of the distant past, the Moon holds a record of the battering that followed. The myriad craters that line the lunar surface tell of time up to 4 billion years ago, when Jupiter and Saturn hurled a barrage of objects toward the inner solar system.
A recent study draws on the sizes and number of lunar craters to model the impacts endured by Earth. At least four impacts would have been large enough to remake the surface of our planet and to radically alter the course of its history. (intense music) Smashing into a crust rich in radioactive uranium and potassium, they tore these elements from the planet and sent them into space.
(intense music) This process, called impact erosion, left a crust that would cool more quickly when the impacts finally died down. Less disruptive impacts are thought to have carried in massive amounts of water, or released water bound to minerals deep below the surface. (thoughtful music) Half a billion years after the birth of the Moon, Earth has become a world of water.
It seas span every horizon, broken only by volcanic islands. (waves rumble) The Moon, still in close orbit, whips up tides that lash rocky volcanic shores. (thoughtful music) Earth's atmosphere is a mix of hydrogen, nitrogen and carbon dioxide, laced with water vapor.
Land and sea are rich with chemicals, carbon, nitrogen, oxygen, iron and more, that came with the damn of the solar system. (thoughtful music) The Earth has what it needs to accomplish its ultimate feat, to nurture life. But there's a problem.
(thoughtful music) Its water is slowly disappearing. (intense music) The young Sun, while dimmer than it is today, is prone to powerful flares. (intense music) They strike the Earth's upper atmosphere.
When a solar particle hits a water molecule, H2O, it can blast it apart. Lightweight hydrogen wafts into space, while heavier oxygen sinks to the surface and binds with rocks. (thoughtful music) We now know what a devastating effect this can have.
Spacecraft observations show that Mars, long ago, harbored ample stores of water. (thoughtful music) Its surface is etched by the meandering paths of ancient rivers and lined with sediments laid down on lake and ocean beds. Mars today is a lifeless world, graced with a thin carbon dioxide atmosphere, there is little or no water left.
(thoughtful music) Using special sensors orbiting spacecraft have documented the ongoing loss of water in Mars's upper atmosphere, stripped by solar radiation. (thoughtful music) Scientists have observed this same process of work on Earth's sister planet, Venus. (intense music) The result, Venus's atmosphere today is a witch's brew of noxious chemicals, including thick sulfurous clouds.
(intense music) Down at the surface Venus's atmosphere is choked with high concentrations of carbon dioxide, a potent greenhouse gas that traps the Sun's heat. (intense music) CO2 has turned Venus into a cauldron. With surface temperatures of almost 500 degrees Celsius, Venus is the hottest planet in the solar system.
(intense music) This hostile environment is reinforced by active volcanoes that dot its surface, spewing sulfur and carbon dioxide. (intense music) How did Earth avoid such a grim fate? For one, our planet has a protective shield that both Venus and Mars lack.
(intense music) It's a magnetic field that deflects the most powerful waves of radiation the Sun can throw at us. Generated by the exchange of heat between Earth's core and its crust, this magnetic field is a legacy of rapid surface cooling early in the planet's history. It's just our first line of defense.
(volcano rumbles) Another line of defense began to simmer away across the surface of our planet as early as 4 billion years ago. Life. (soft music) Long standing theories see life's crucible in the stirrings of undersea volcanic vents.
Heat and chemical reactions over long periods of time produced proteins and nucleic acids, the chemistry of life. (soft music) More recent ideas point to hot springs and other volcanic features that dotted the land masses of early Earth. (soft music) No one knows exactly how or where life gained its first foothold.
(soft music) What we know is that it did emerge and that it spread thanks to a key breakthrough, the ability to turn sunlight into energy. (soft music) Photosynthesis, the process that fuels plant life, made its first appearance in simple bacteria over 3 billion years ago. (soft music) Using one of the world's most powerful super computers scientists have sought to model its chemical secrets.
(soft music) Step one is to capture sunlight. Passing through a transparent membrane to the center of the bacteria we encounter a cluster of spherical pods. Each one is equipped with special sensors designed to harvest solar energy.
When a photon hits it excites rings of chlorophyll molecules. (soft music) This energy is transferred across a family of proteins, the machines of life. (soft music) Down the line electrons and protons carry the energy through a chain of chemical reactions.
(soft music) The energy driving these reactions came from the Sun. The cell must now convert it into action. It's the energy stored in protons that gets things moving.
(soft music) Streaming into watery spaces within the cell they flow toward a towering molecular structure. As they enter their electrical charges turn a protein like a crank. This turning motion initiates a chemical reaction, one that is essential to all life on Earth.
Two molecules join to form a third called ATP, shown in in blue. It is the universal energy currency in every cell that has ever lived. Like a biological battery ATP stores energy captured from the Sun, repackaged in a stable form that the cell can now use to break down food, to power locomotion, to fuel reproduction, to live.
(soft music) ATP made it possible for microorganisms to flourish and evolve. (soft music) As bacteria gave rise to plants, a more advanced form of photosynthesis released a byproduct. Oxygen.
(soft music) This new supply of free oxygen surpassed the amount absorbed by the land and the oceans. In the atmosphere it bound with hydrogen, preventing its escape into space while forming a new molecule of water. (soft music) This process would gradually stem the loss of Earth's oceans, though not completely.
A recent study concluded that our planet has still lost up to 25% of its original stores of water. (soft music) Across the surface of our planet water began to work in tandem with life, the Sun and geology to power a remarkable planetary engine. The climate.
(soft music) The climate is driven in part by the unevenness of solar heating due to the cycles of day and night, and the seasons. (soft music) These factors moderate global temperatures, sending warm tropical winds toward the poles and cold polar air toward the equator. (soft music) Tides and currents mix cold water from the deep with the warm surface.
Solar energy is trapped in the atmosphere by water vapor, along with carbon dioxide, the greenhouse gas that ruined Venus. What keeps CO2 in check is the special ingredient that sets Earth apart, life. (soft music) The oceans are chalk full of it.
(soft music) Microscopic phytoplankton take in CO2 driven into the ocean by waves or drawn up from the deep by currents. (soft music) They send the carbon atoms on a journey up the food chain. Phytoplankton get eaten by zooplankton, like these Radiolarians, a creature that dates back to a time over 500 million years ago, when life exploded across Earth's oceans.
Moving up in scale Copepods are tiny bug like crustaceans, and the single largest source of protein in the sea. Octopus larvae are part of a vast zoo of creatures, smaller than the tip of your finger. (soft music) They get eaten by small fish and they in turn by larger creatures.
(soft music) At each step in the food chain the carbon that began as part of a diffused gas in the air is passed onto larger and larger animals. The larger the body, the greater the mass of carbon. (soft music) From whales down to tiny phytoplankton, marine life is part of a global system of removing CO2 from the atmosphere then gradually releasing it back.
(intense music) The key to this carbon cycle is Earth's ability to store it long term. (intense music) A NASA satellite is tuned to read chlorophyll, a chemical tracer for plant growth. In sync with the seasons plants take in vast amounts of carbon dioxide while releasing the oxygen we breathe.
On land carbon finds its way into the ground when plants and animals die and decay. The Earth too gets into the act. (intense music) Exposed rocks take in CO2 when it rains, erosion sends it into the oceans.
(intense music) If it becomes part of the marine food chain carbon rich matter can sink all the way to the sea bottom in the form of waste. (intense music) In time carbon rich sediments can turn to oil, or to rock, like limestone. Carbon can return to the environment if rocks become exposed or if the Earth begins to erupt.
(intense music) Every year over 100 million tons of carbon dioxide are spewed into the oceans and atmosphere by volcanoes. (soft music) Acting on time scales of a day to millions of years the carbon cycle has helped to make our planet habitable. Its success depends on life itself.
(soft music) Earth today, endowed with ocean, atmosphere and land. With light and warmth. With life that's bountiful and in balance.
(soft music) As we study the intricacies of what makes our planet tick we marvel at what it took to achieve all that. (intense music) The aftershocks of supernova. (intense music) The violence of Jupiter.
(intense music) A chance collision. (intense music) And the gift of a moon. (intense music) Of water and life.
(intense music) The more we're able to reconstruct our planet's past the more singular it seems. That is until we realize how many other solar systems are out there. (intense music) We ask, is Earth just one of countless habitable worlds in a galaxy bursting with life?
Or is it a wondrous twist of fate? A remarkable convergence of chemistry, energy and chance? Our planet became a paradise, but is it the only one?
