How Old Is It - 06 - The Solar System

in how older stars we found that the Sun will burn hydrogen for 10 billion years but because the Sun is a field star we could not determine how long ago the hydrogen burning started in how old is the earth-moon system we found that the oldest solid earth and moon material was 4.3 billion years old but we could not determine the age of the earth from its original start because the giant impact turned the mantle to magma in this chapter will cover the age of the solar system itself which will give us both the age of the Sun and the age of the earth to get a handle on the age of the solar system we'll need to review planetary formation theory and each such theory would need to explain our solar system as we see it today we'll start with a look at some of the key characteristics of our system we have the Sun at the center and for relatively small rocky planets in the inner solar system and for much larger gaseous planets in the outer solar system they are all in nearly circular orbits and they are all in the same orbital plane none of the planets are orbiting outside the plane like some comets asteroids and dwarf planets do our theory of planetary formation will need to explain these facts in our how older stars segment we covered how the circumstellar disk feeds the central object leading to the formation of protostars Tatari stars and eventually fully formed helium fusion burning stars the process from the beginning of the protostar phase to a fully fledged star is estimated to take from 1 to 200 million years during this period the debris in the disk is forming planets in the nucleosynthesis segments of the lambda cold dark matter Big Bang Theory chapter we covered the content of clouds like these for the first generation of stars at that time it was limited to hydrogen some helium and just traces of beryllium and lithium planetary nebulae form when normal stars run out of hydrogen the violent process created pressures and temperatures large enough to fuse hydrogen and helium into heavier elements and eject them into the interstellar medium from which giant molecular clouds like this are formed these include carbon nitrogen and oxygen along with even smaller amounts of heavier elements like silicon and sulfur and iron but this kind of star transition does not have energy to fuse enough protons to create atoms larger than iron supernova explosions occur when supermassive stars run out of hydrogen these seed even heavier elements into the interstellar medium like LED Circo Neum silver tungsten and gold but even at these extreme energies it is unlikely that a supernova could produce elements larger than land this is because of the repulsive force of light charges is so strong the Coulomb force creates the Coulomb barrier you may recall from our last chapter on how older stars that a proton in our Sun can collide a trillion times a second with other protons and still not fuse for a billion years but neutrons have no charge and they're fusing has no such barrier it has long been theorized that the heaviest elements like thorium protactinium and uranium were created by neutron star mergers in 2017 using large laser interferometers that we covered in the gravitational waves segment of the how fast is a video book just such a merger was detected now known as a key lanova it's understood that neutron star mergers are the origin of the majority of all the heaviest elements found throughout the universe for our collapsing cloud we know that it contained all 94 natural elements because we find them here on earth 99% of the mass of the circumstellar disk is in the form of gas with just 1% in the form of dust the solid dust has little effect on the star formation but it's key to planetary formation dust is the only solid grains available for growing planets dust itself cannot be formed directly from purely gaseous material at the low densities found in interstellar molecular clouds instead solid grains are known to form in planetary nebulae supernova and in the outer atmospheres of cool supergiant stars the dust in the interstellar medium extinguishes light from stars via absorption and scattering the scattering leads to emissions of their own comparing dusty clouds to non dusty clouds using spectral absorption and emission lines shows that almost all the iron magnesium silicon much of the carbon and some of the oxygen and nitrogen are contained in the dust this makeup is similar to the terrestrial amorphous non crystalline rocks if the temperature permits they are surrounded by a mantle of water ice the original dust grains in the cloud are no longer available for direct observation but to this day there are similar objects in our solar system called interplanetary dust particles they are being collected in the thermosphere by the International Space Station here's an electron microscope view of one of them it's 10 micrometers in length that's around a hundred times larger than interstellar dust NASA also uses high-flying aircraft to collect dust at high altitudes before it gets close enough to the surface to mix with earth elements in 2018 the team of scientists from the university of hawaii examine this dust with electron microscopes they mapped the element distributions and discovered that these glassy grains are made up of sub grains that aggregated together prior to the formation of the comet the interplanetary dust particles came from these represented samples of the early interstellar dust dust is the base material for planet formation the dust grains run into each other and stick forming larger and larger grains mixing compounds and eventually forming mineral rich pebble sized objects that grow to Boulder size the near-earth asteroid 2015 TC 25 is an example of an object this size with a 4 meter diameter that's 13 feet it's one of the smallest asteroids ever detected the process continues to grow the rocks into rubble heaps large enough for a little gravity to hold them together ru is an example of an object this size it's one kilometer wide and weighs in at just under a half a trillion kilograms Japan landed rovers on this asteroid in 2018 you can see the rubble nature of the object with this picture taken from the surface by the time enough matter has accumulated into objects like these we have what astronomers call planetesimals these can extend from several to hundreds of kilometers in diameter Comet 67p visited by the rosetta mission in 2014 is thought to be a combination of two planetesimals that bound together in a slow speed collision their combined mass is just under 10 trillion kilograms this is a ROKAF it was discovered in 2014 out in the Kuiper belt by the new horizons search team using the Hubble Space Telescope this object is 36 kilometers across that's 22 miles it's considered a minor planet like Pluto like p67 it has two lobes that collided slowly a close examination of the surface shows lighter lines separating sections of the lobe these indicate that a rock auth was built piece by piece by the coalescing of over a dozen smaller planetesimals [Music] by the time this collide and merge process creates objects with enough mass to produce a gravitational strength that exceeds the structural strength of the rocks the object is forced into a spherical shape Ceres is a good example of this and once the mass reaches around fourteen billion trillion kilograms solid mass convection activates the temperatures and pressures inside the object liquefy matter and the core becomes molten mercury our smallest planet is a good example of this the star Fomalhaut is a good example of this process his circumstellar disk morphed into a protoplanetary disc with at least one object large enough to be considered a planet formal he'll be over time these larger objects continue to grow by accumulating matter from the disk we find that in each region each orbit each distance from the Sun everything coalescence into one massive object these larger objects sweep out the remaining debris in their orbits this is a defining characteristic for planets all the little deviations averaged out as the smaller particles with varying elliptical orbits combined this explains orbits being nearly circular and all in the same plane but the actual process is very chaotic not as simple and straightforward as this illustration the process of accumulating matter in the disk into larger objects came to an end when the Sun ignited as a main-sequence star and it's strong solar winds blew away any remaining loose material computer model estimates for how long this process takes range from 100 million to 200 mm years here's a computer simulation created by Caltech that illustrates this chaos planets interact with a rotating disc and lose momentum moving their orbits closer to the Sun or gain momentum increasing their orbital distance from the Sun changing orbits create collisions between planets moons form and collide with each other and with planets comets and asteroids form and smash into everything but out of this chaos we get our current order there is an expected difference between how this works out for planets forming in the inner parts of a solar system and how it works out for planets forming in the outer parts of the solar system in the inner parts closer to the central star is hot at these temperatures with no pressure water molecules cannot take liquid or solid form the solar wind from the forming star pushes these molecules along with helium and hydrogen molecules into the outer solar system planetesimals in this inner region wind up with little to no gas or water that leaves metal and rock for these planets in the outer parts further from the central star the water is frozen solid and therefore behaves like rocks planets out here have metal rocks and ice this means that they're substantially more massive this extra mass produces enough gravity to hold on to the gas as well the dividing line is called frost line with a snow line and it's distance from the star is temperature dependent it will be located where the temperature falls to around 250 degrees Kelvin that's minus 10 degrees Fahrenheit the hotter the star the further out this line will be this explains the difference between the rocky planets in the inner solar system and the gas giant planets in the outer solar system our frost line is between 4 & 5 astronomical units that puts it at the far rim of the asteroid belt meteorites are asteroid or comet material that have fallen to earth there are over 40,000 meteorites that we know about some have no uranium they can be used to measure the solar system's initial lead ratios the canyon Diablo meteorite fits in this category some contain intact material from the circumstellar disk during the planetesimals impress these are the ones that never went through a melt and re hardening process like all the rocks on the earth and the moon the meteorite Ilan D fits into this category we'll start with Canyon Diablo the meteorite that was responsible for meteor crater in Arizona it is estimated to have fallen to earth around 50,000 years ago fragments of the meteorite have been actively collected since the mid 1800s the largest fragment is the Hollinger meteorite with a mass of 639 kilograms or 1400 pounds this iron meteorite contains trail light an iron sulfide mineral that has almost no uranium since the mineral contains no uranium all the lead present in the tree alight is the lead originally present when the meteorite formed this includes the radiogenic isotopes at 206 and 207 that decayed from uranium before the meteorite formed as well as the natural non radiogenic led to o4 thus using mass spectrometry as always this Canyon Diablo troilite gives us the primordial ratios for lead 206 / 204 and 207 / 204 in fact these two numbers are generally used as the standard for our solar system's original led concentrations in 1969 a Hyundai created a fireball over the northern Mexico sky as the meteorite burst numerous fragments rained down around the small village of Pablito a hyundai over 2,000 kilos of debris have been found and new pieces are still being discovered every now and then it's a type of meteorite called carbonaceous chondrite that's a stony meteorite with lots of carbon in containing small mineral granules called chondrules a lot of meteorites have experienced significant heat that melted and reorganized their minerals but on day was not one of them its pieces remained as they were when they formed here's a slice of it we're particularly interested in the little pale whitish gray bits called calcium aluminum inclusions CA is for short these are thought to be the very first solids condensed in the circumstellar disk dating these would give us the starting date for the solar system but they're interesting pieces of the meteorite are these round darker grey bits these were the first liquid droplets to condense out of the disk gas they are also some of the oldest minerals that formed in the solar system but not as old as CA is we are interested in to findings associated with a hyundai one is the ratio of uranium 238 to uranium 235 isotopes in the on day it was around one hundred and thirty seven point eight eight uranium 238 for each uranium 235 this ratio has held up across earth moon and meteorite rocks the other is the ratio of radiogenic lead 207 and 206 to non radiogenic than 204 a large number of these ratios were determined from the various CA is and chondrules who will use just one with lead 207 over 204 at twenty two point seven six and 206 over 204 at thirty point zero six these ratios for uranium and lead from a Yan day and primordial lead from Canyon Diablo are very important for dating meteorites only how old is the earth-moon system we covered radioactivity half-life and the law of radioactive decay it showed that the present amount of radiogenic led in a sample will equal the initial amount plus however much gets created by the decay of the parent uranium for lead 207 the parent is uranium 235 for lead 206 the parent is uranium 238 with this equation we used Arthur Holmes system for uranium decay into lead inside zircon crystals to date the oldest rocks on the earth and the moon but that won't work for meteorites they don't have any zircon crystals so by the mid 1940s Arthur Holmes and others that extended the uranium-lead dating method into a lead lead method called the Holmes how Turman system that took into account led to owe for the natural non radiogenic lead isotope this is the system that tells us the age of meteorites the earth planets and the entire solar system so we'll take a minute to show how it works the idea is to start with the uranium to lead growth equations and produce an equation that fits the definition for the slope of a line we start by dividing both sides of the growth equation by the number of bled 2:04 isotopes we move the lead term on the right side of the equation to the left side leaving only uranium on the right we then divide the top equation by the bottom this creates ratios on the left and right we then replace the uranium ratio on the right with the known value 1 over 137 point 8 8 found in a yon day and elsewhere this knocks out the need to measure uranium content altogether if we graph this equation using the 207 to 204 ratio as the y axis and the 206 to 204 ratio as the x axis we see that the left-hand side of our homes how durman's equation is the slope of a straight line the right-hand side depends only on time for any given time T will have a straight line replacing the initial lead ratios with the standard from Canyon Diablo we see that all lines pass through this point now if we have T stand for the amount of time since the material formed we can use the present-day lead ratios from the I on day CA I for the other point on the line other ratios from a on day CA is also fall on this line in fact all the materials formed around time these CI is formed will fall on this line that's why this isochron is called the geo cron it represents the age of the solar system's planetesimals building blocks so now we have an equation for this earliest time T is a transcendental equation cannot be solved algebraically the computer iteration processing gets us as close as we want the solution gives us T equal to four point five six seven billion years plus or minus 70 million years this is the oldest age of all meteorites meteors asteroids comets moons planets including the earth as well as the Sun in fact whenever you hear that the Sun is four-and-a-half billion years old that number came from this homes how durman's process for radiometric dating now that we have a handle on star development from how older stars and some key dates from uranium lead analysis of rocks and meteorites we can estimate the age of the solar system as a whole give or take a few million years here and there our first data point is provided by uranium decay a neutron star merger would have seeded our cloud with relatively equal amounts of uranium-235 and uranium-238 the time it takes for the ratio to reach today's value of one uranium 235 for every one hundred and thirty seven point eight eight uranium 238 is six billion years for almost 1.4 billion years the cloud orbited the Milky Way in hydrostatic equilibrium and then for some as yet unknown reason the equilibrium was broken and it started to collapse within a million years the colliding giant molecular cloud broke up into fragments with our fragment being one of them over the next million years a circumstellar disk formed around a central object accreting mass from the disk material orbiting around it from here on we'll cover the development of the core object and the circumstellar disk in parallel over the course of the next million years the central object continued to accumulate matter and its core temperature reached ten thousand degrees Kelvin at this temperature it began to shine by a normal non-nuclear means that made it a protostar it may have looked like this one just nine hundred and fifty light years away during this time most of the matter continues to reside in the circumstellar disk it's losing large quantities of material to the central object but by the time the protostar forms the disk still has 99% of the solar system's mass some dust may have been colliding and sticking together but the vast majority of whatever formed in the disk during this period was eventually lost to the forming star the protostar phase does not last long for stars the size of our Sun over the next million years it accumulated massive amounts of matter from the disk and shrank significantly as gravity took hold his core temperature rose to five million degrees this put the Sun into its teatari phase named after the star dattari in fact it may have looked like Qatari the young Sun was still growing by accumulating large amounts of material from its surroundings so it was not yet stable unlike the short lifespan for protostars t-tauri stars could last for a hundred million years during this phase the disc experienced a growing solar wind from the developing star this wind started pushing on the lighter gas and dust close to it forming a snow line beyond which water ice could form with the Sun at only 5 million degrees Kelvin this line would be much closer to the star that it is today over the next 30 million years the sun's core temperature would have reached 10 million degrees throughout the disk some dust grains began to stick together forming larger particles these particles continued to randomly collide and stick creating planetesimals reaching the size of boulders or small asteroids [Music] the oldest of the starting material found so far was in the Ilan day meteorite and dated by a lead isotope contents to be four point five six seven billion years old by convention astronomers use this date for the age of the Sun and its solar system often round it up to 4.6 billion years estimates are that the Sun remained in its teatari phase for an additional 67 million years as it migrated to the main sequence in that time it reached 15 million degrees Kelvin at its core as the sun's solar wind picked up it dispersed the remaining gas and dust around it back into the interstellar medium this ended mass accumulation and the Sun settled into hydrostatic equilibrium during this period in the disk the forming of planetesimals increased as the objects began to attract each other via gravity objects grew to Planet sizes and swept out the debris in the vicinity of their orbits the disc experienced a chaotic period of collisions that resulted in nine major planet sized objects along with dozens of moons and millions of asteroids and comets in addition as the Sun heated up the snowline moved out to where we find it today just outside the asteroid belt this line separated the four waterless inner solar system planets from the five water rich outer solar system planets the giant impact hypothesis has a collision between the Earth and a mars-sized planet liquefying the crust of both planets and forming the moon from ejected matter based on uranium-lead dating of zircon crystals found in Australia and on the moon this happened 4.3 billion years ago that would be 200 million years after the original earth formed given the mass of our Sun we know that in the beginning it had enough hydrogen to shine for a total of 10 billion years we now figure that it has been burning for 4.6 billion years therefore we can expect that it will burn for 5.4 billion more years before it runs out of fuel I'm impressed by how we have been able to reconstruct our solar system's formation we started with a giant molecular cloud rotating around the Milky Way every 213 million years 26,000 light years from the center it was seeded with uranium around here a little over an eighth of a revolution from our current position it rotated an additional six and a half times before the cloud segment started to collapse here where we find the Perseus arm today it took only half of a revolution more to form the entire solar system today we have a beautiful planet with a Sun that will sustain us for billions of years but even more spectacular than the rise of the earth over a 300 million year period is what happened in the 4.3 billion years since our temperate watery earth formed life [Music] you

Channel: David Butler

Views: 78,382

Rating: 4.84199 out of 5

Keywords: STEM, Astronomy, Allende, uranium, lead, rocks, solar system, sun, planet formation, circumstellar, dust, planetesimals, planet, solar wind, Snow Line, meteorite, Holms

Id: ZeA4X59_zdc

Length: 32min 6sec (1926 seconds)

Published: Tue Jun 16 2020