the stuff you see around you is all a complex composition of billions upon billions of atoms each atom has different properties which are determined largely by the number of protons contained in its nucleus this is how the periodic table of elements something anyone who's taken a chemistry class is familiar with is organized but as i showed in my previous video the universe shortly after the big bang only consisted of the lightest elements hydrogen helium and lithium along with some of their isotopes yet we find in nature today elements as heavy as california element 98 on
the chart how is this possible if no atoms heavier than lithium were created at the beginning where did all these elements present in the universe today come from and perhaps most importantly where did carbon nitrogen and oxygen the elements that enabled life to exist and for creatures like us to even ask this question in the first place come from the fascinating journey of the life-enabling atoms of the universe is coming up right now first i'd like to thank this week's sponsor magellan tv one of the videos that inspired this subject for me is called sun
and math it's a two-part series the first of which takes you on a fascinating journey from the big bang to the birth of the sun to the start of life on earth and then to the dawn of man and how the sun has played a critical role throughout our history and culture magellan is a new kind of streaming documentary service created by the filmmakers themselves you'll not only find science videos like sun and man but also thousands of other videos on subjects like history nature travel and technology magellan has a special holiday offer right now
for arvanash beers you can get a buy one get one free gift card for an annual membership it's a great gift that you can give to someone that will cost you nothing if you sign up for a year it's just here for the holidays so be sure to take advantage of this by clicking the link in the description you should be aware that the origin of the elements of the periodic table is an active area of research we're still learning the details so what we'll discuss here is based on the best theories we currently have
in a recent video we looked at the early universe and the events that led to the first atoms being formed check out that fascinating story if you haven't already there are 118 known elements as of today but the heaviest 20 do not occur naturally they are man-made in labs but that still leaves quite a few to build the universe with 98 elements where did they come from well let's first look at where the very first atoms came from in the first minutes after the big bang nucleosynthesis occurred this is the process in which newly formed
protons and neutrons started to form nuclei or the cores of what would later become the first atoms at this point we didn't have neutral atoms but only the charged nuclei of atoms mostly protons which are the nuclei of hydrogen atoms they were positively charged without any electrons orbiting them this nucleosynthesis process occurring only minutes after the big bang produced only light nuclei about 75 percent were just single protons or hydrogen nuclei and 25 helium nuclei consisting of two protons and two neutrons and a few other isotopes were also produced in trace amounts the big bang
nucleosynthesis ended when the universe was only about 20 minutes old we mainly had only the nuclei of hydrogen helium at this point but from all these light nuclei near the beginning all the atoms we have today were formed how did this happen well after the first 20 minutes the universe needed to cool down substantially from about 5 billion kelvin to about 3 000 kelvin this took about 380 000 years at this point a process called recombination took place this was the point when the universe was cool enough for the nuclei to capture electrons to become
neutrally charged atoms instead of just free-floating charged nuclei and electrons in a plasma state prior to this energies and temperatures were too high for electrons to stay bound around nuclei so that's how we got the first atoms in the universe but we basically only had the first two elements of the periodic table so now we need to account for the remaining 96 naturally occurring elements going back to recombination after this period in the history of the universe the universe became dark in that there were no stars at this point but soon enough as hydrogen gas
condensed into the first stars the universe came out of the dark ages and these stars began to shine stars shine thanks to a process called fusion in the first stars this happened when hydrogen atoms combine to form helium atoms this process takes place in the core of stars where temperatures and pressures are high enough to initiate fusion this process releases energy in the form of heat and light i made a detailed video on how this process occurs in our own sun if you're interested in the details the process happens something like this you start with
four hydrogen atoms and then with the help of the weak force which can turn a proton into a neutron you can fuse two pairs of hydrogen atoms into two deuterium atoms which is just an isotope of hydrogen with an extra neutron then you can borrow two more hydrogen nuclei or protons and fuse this with deuterium to form two helium-3 atoms which is an isotope of helium containing just one neutron instead of two then you can fuse the two helium-3 atoms together releasing the two protons you borrowed and the end result is a stable helium atom
the helium-4 atom along with the two protons energy is also released during this fusion process now as it turns out you can continue this fusion process to make heavier and heavier atoms you might think it was the sun that produced all the other elements of the periodic table thanks to this fusion process well that's not quite the case it's more complicated than that stars like our sun which is only a medium-sized star compared to other stars we can observe are only able to continue this fusion process up until elements like carbon or nitrogen are formed
why does it stop there the problem has to do with energy you get a lot of energy from fusing hydrogen but as you start to fuse heavier elements the energy you get becomes less and less a star is just fighting to survive the battle between two forces gravity which tries to collapse the star and radiation pressure from the fusion process which counteracts gravity and tries to explode the star so it's a kind of tug of war between these forces a balancing act smaller stars cannot produce enough energy or radiation pressure when fusing heavier elements and
thus lose the battle against gravity they eventually collapse and become small white dwarfs at this point fusion stops the stars cool and shine no more bigger stars however can win the battle up to a point as large stars begin to die different elements are produced in layers or shells within the star so for example there would be a layer of oxygen calcium silicon and so forth due to the higher gravity and temperatures the heavier nuclei will be synthesized closer to the center while lighter elements will be made closer to the surface at some point though
even in bigger stars the fusion process requires more energy than the energy produced from fusion large stars can produce elements up to iron but the process stops there why unlike the lighter elements before it iron releases no energy when fused this is because iron has the largest nuclear binding energy of all elements in other words it has the most stable nucleus so the fusion process stops at iron and the bigger stars also die but it's still remarkable that stars in their core can take hydrogen as the main ingredient and eventually fuse them to form elements
up to around iron now you might say well this explains less than half the periodic table what about the other elements for this we have to consider other details such as what happens when stars reach the end of their life when a massive star that is one that can continue the fusion process up to iron dies they explode this can be seen even on earth it's a supernova as a dim star can briefly shine with the luminosity of an entire galaxy but this bright light lasts very briefly usually no more than two minutes how does
this happen when a massive star runs out of fuel it cools off this causes the outward pressure from the energy of fusion to drop gravity wins out in the tug of war between it and outward pressure and the star suddenly collapses imagine something a million times the mass of the earth collapsing to the size of a large city 30 kilometers in diameter and something like 15 seconds the collapse happens so quickly that it causes enormous shock waves that cause the outer part of the star to explode leaving a small dense core usually a neutron star
or black hole elements beyond iron are not usually produced in the core of stars but are formed in this explosion the extreme temperatures in a supernova can reach billions of degrees this drives additional nucleosynthesis of elements heavier than iron and actually the latest research shows that even most of the iron on earth actually comes from these supernovae explosions as well and not from the core of stars this supernova yields elements from iron all the way to zirconium element 40 which is a lot heavier than iron element 26 note when i say heavy in terms of
elements i mean the atom is bigger it contains more protons and neutrons smaller stars like ours with less mass don't end their life like this as mentioned earlier they can only produce elements up to about nitrogen when such smaller stars are dying their cores collapse as their nuclear fuel starts to run out this causes the outer layers to expand into a red giant in a few billion years our own sun will become a red giant expanding all the way perhaps to earth's orbit this outer layer containing elements up to nitrogen will eventually evaporate into space
and a small object about the size of earth called a white dwarf will remain these are very dense bodies the size of earth but with a sun-like mass and are a thousand times less bright than the sun so now we've accounted for most elements up to zirconia so where do the rest come from it turns out that smaller stars like our sun have another trick of their slave by which they can produce heavier elements you have to remember that stars like the sun are made from the remnants of previously exploded stars typically in a nebula
composed of gases from many exploded stars of the past so although the sun doesn't produce elements much heavier than nitrogen it contains heavier elements even up to iron because these were present in the original gases from which it was formed and as you might have guessed there are more ways to produce heavier elements than just fusing two atoms together low-mass stars produce excess neutrons as a by-product of fusion and because they are neutral in charge it is relatively energy efficient for a free neutron to get captured by the nucleus of a heavier element when these
green neutrons merge with the heavy elements they produce an even heavier isotope of the element then over time due to the weak force some of the neutrons transmute or turn into protons inside the nucleus this way a heavy element like iron turns into a heavier element like cobalt the cobalt by absorbing more neutrons can turn into nickel this process can continue to make heavier and heavier elements and thanks to this stars can make elements from strontium all the way to lead and bismuth so now we can account for elements all the way up to element
83 but we still have elements heavier than this to explain there is yet another mechanism to produce the heaviest elements the core of a supernova after exploding in some cases can become a neutron star that is a star composed of neutrons it's believed that when two neutron stars merge they can free up a lot of neutrons this abundance of neutrons can get absorbed by heavy atoms near the neutron stars and over time these heavier elements become even heavier as some of the neutrons transmute into protons this process can produce elements all the way to plutonium
element 94. now what about the naturally occurring elements beyond plutonium where did they come from well it turns out that these super heavy naturally occurring elements only have very unstable isotopes so we find them typically only around radioactive sources they're naturally produced in very minute amounts as elements like uranium which is much more abundant absorbs neutrons these neutrons transmute over time to produce isotopes of heavier elements in fact this is believed to be the only source of the naturally occurring elements on earth heavier than uranium the remaining 20 elements that you see on the periodic
table are man-made they do not occur naturally and are highly unstable lasting sometimes only fractions of a second now i should mention that there are three elements namely boron beryllium and some lithium that are not produced by any of the mechanisms that i talked about they are produced when cosmic rays during a supernova explosion split heavier elements and a kind of fission reaction now and even though there are so many elements on the periodic table it's interesting to note that 98 of the visible matter in the universe is made up of only two of them
hydrogen and helium the remaining 96 natural elements make up only two percent of what we can see so most of the atoms in our bodies and on earth like carbon nitrogen and oxygen are part of a minuscule portion of the visible matter in the universe but this does not necessarily mean that life is rare because these are not exotic elements they can be detected throughout the universe for example in nebulae where stars similar to the sun are being formed where planets will also most likely form and they will also be composed of the same set
of elements that we can find right here on earth if life is not abundant in the universe it's probably not due to the lack of any exotic elements and if you have a question please leave it in the comments because i try to look at all of them i'll see you in the next video my friend [Music] you
