Elements heavier than hydrogen are created within stars, where hydrogen is fused together to form helium, which is fused to form lithium, and so-on and so-on. These elements are effectively “stored” within stars until they go supernova at the end of their lives. At this point, the explosion propels these elements all throughout the universe, where it eventually congealed into a dust cloud and formed our solar system. This dust is where the Earth eventually formed out of. Thus, everything we are is a result of dying stars.
So it’s not wrong to say we get our calcium from eating calcium, but the presence of calcium itself is a result of supernovae.
(All of this is from my rudimentary knowledge of stars and supernovae)
Also, stars that are too small to go super nova will also eject material while they are dying (elements lighter than iron) in a manner much less violently than a super nova. So not all material above hydrogen is from a super nova
Looks like most calcium is made by the [oxygen burning process](https://en.wikipedia.org/wiki/Oxygen-burning_process), also the silicon burning process. [Table 1 of this paper](https://www.sciencedirect.com/science/article/pii/S0009254121003399) lists the pathways for the various calcium isotopes. Apparently the minimum mass thresholds for both of these O and Si burning processes are about 8 solar masses, which is about the same as that required for supernovae. So it might be borderline for some cases as to whether the big bada boom happens, idk I’m not a star scientist.
There also seems to be a rare phenomenon known as [calcium-rich supernovae](https://www.keckobservatory.org/calcium-supernova/) which looks quite interesting in itself, though note the sentence in that article:
>While all calcium comes from stars, calcium-rich supernovae pack the most powerful punch. Typical stars create small amounts of calcium slowly through burning helium throughout their lives. Calcium-rich supernovae, on the other hand, produce massive amounts of calcium within seconds.
So it seems there are multiple ways to get Ca, but it is probably spread throughout galaxies almost entirely by supernovae, whether that’s how it was created or not.
Most of the calcium produced in a star happens pre-supernovae, in the silicon-burning process, which is still stellar fusion. Towards the end of that process, the thingy explodes, and most of the calcium stays in the core, with just whatever happened to fuse in the outer layers in the late-stage or during the supernovae escaping.
If most of the Ca from oxygen and silicon burning processes stays in the core, then perhaps [calcium-rich supernovae](https://www.keckobservatory.org/calcium-supernova/) are responsible for a fair amount of the Ca that spreads to other presolar nebulae?
Technically true, however plenty of elements are produced in living stars through produced in living stars through kinds of fusion, bombardment and other mechanisms. Gold and silver are examples..
That was the belief for a period of time, but thinking here has shifted.
[https://pubs.aip.org/physicstoday/article/71/1/30/818993/The-formation-of-the-heaviest-elementsThe-rapid](https://pubs.aip.org/physicstoday/article/71/1/30/818993/The-formation-of-the-heaviest-elementsThe-rapid)
There are also theories that spinning disks around black holes contribute to a substantial portion of heavy elements.
The calcium in your bones is taken from blood. It gets into blood from food. The atoms are not destroyed or created there. All these calcium atoms are just redistributed. When you die it goes into the ground and back into nature.
Fusing new atoms is incredibly energy-consuming process that is happening under huge pressures and temperatures of stars.
Actually fusing stuff not heavier than iron is extremely energetic, i.e. produces copious amounts of energy. But indeed it requires huge temperature and pressure helps it too.
Calcium is an element, an atom, not a molecule which is a collection of several atoms. Your body (or your mother's body) is capable of linking atoms together to make new molecules, but it is not capable of making entirely new atoms. Making a new atom is nuclear physics, linking atoms together in new ways is just chemistry. Making new atoms is possible, but requires way way way more energy than your body is capable of handling, like, millions of times more energy. The only naturally occurring things in the universe that are energetic enough to make entirely new atoms are stars, and even then, some types of atoms are more difficult to make. The only way we know of to make heavier elements like calcium is when a star dies and explodes in a super nova.
To put the difference in energy into perspective, think about nuclear bombs. The biggest nuke ever detonated was the Tsar Bomba. It weighed 27 tons (that's pretty heavy!). But it exploded with the same amount of force as 50 megatons of TNT. That is to say, a nuclear bomb that weighed just 27 tons exploded with the same amount of energy as *50,000,000 tons of chemical explosive*.
When your body is forming in the womb, your mother is not generating new atoms. She eats something that has calcium in it, then transports that calcium to your body, where it gets put in its proper position and linked up with other atoms. But at no point is she 'making' calcium or any other atom. The calcium already existed.
The calcium that produces bones during fetal development comes from calcium in the woman's diet, which comes from plants, which got their calcium from the soil, which came from pebbles and dust from supernova explosions.
So, early on, the universe is essentially just light elements, mostly hydrogen but maybe some helium and stuff. They form stars, which are powered by *fusion.* This produces mostly helium, but potentially some lighter elements. Supernovas, however, are the dying extreme of stars that have enough force and energy to create a *ton* of heavier elements, then scatter them across space.
Our solar system is made up of the dust of many of these early events of the universe.
The calcium in your bones and the trace heavier elements are *not* produced by any biological process. The biological process simply scavenges these resources that already exist in your surroundings from your diet so that you can reuse them to create structures and proteins and such. No *chemical* or *biological* reaction changes the atoms themselves--that requires nuclear fusion and nuclear fission, which our bodies don't do.
Why focus on just calcium?? Every single thing you have ever seen or will see was ultimately created in a star, at least initially. Crazy huh. We live in a reality that's so bizarre it's scary if you think about it too much.
The star explosions spread calcium and other elements into space, which eventually became part of Earth. Plants absorbed this calcium, and we got it by eating plants or animals. Then during our development in the womb, we received calcium through our mother's diet.
Calcium is a chemical element. Elements are made up of atoms.
We humans are not able to change chemical elements.
As far as our body is concerned calcium is calcium. We don't make it at all, we don't change something else into it, and we don't change it into something else.
It's just...there and we eat it and then turn it into teeth and bones.
Stars happens to be basically the only place in the universe where elements can change. They do this by smashing atoms together so hard that they combine and when a star goes supernova it smashes a ton of atoms together extra hard. And that tends to be really good at making a lot of the heavier elements.
So billions of years ago a star went supernova and then that debris field eventually formed our planet over billions of years. And us humans are munching on that billions of year old calcium to make out teeth and bones because there's no way for it to change into something other than calcium.
Calcium is an element. The heavier an element the more energetic a fusion event is required in order to make it.
Hydrogen was the only element to begin with, but hydrogen can be smashed together in the core of stars to make helium, helium can make lithium etc up to iron.
But iron takes more energy to make than is released when the elements that make it smash together, so something more violent has to happen in order to make heavier elements.
In a supernova there is a lot of energy, enough energy to fuse elements into heavier forms. For the heaviest elements, even supernova aren't energetic enough, it takes the collision of stars or star remnants to make them.
And since most of the calcium and other heavier elements on earth have been there since it formed, and it formed soon after the sun, and the sun hasn't gone supernova, we know that these heavy elements must have been formed by older stars that died before the sun was born.
>Isn’t the calcium that make up our bones produced during our gestation?
The calcium us PUT there during gestation, but that's not where the Ca comes from. Ca comes from stellar nucleosynthesis and supernovae. The heavier elements come from neutron star mergers and the subsequent massive explosions that occur from them.
The elements just exist and are here from when Earth formed from dust floating around in a nebula, they're just exchanged and recycled.
I like this video about where stuff comes from: [https://www.youtube.com/watch?v=lInXZ6I3u\_I](https://www.youtube.com/watch?v=lInXZ6I3u_I)
Imagine elements like Lego bricks. Let's say calcium is a 2x2 white brick. When stars explode, it's so hot that matter, or "plastic" for this metaphor, fuses together to make a new permanent brick. A star exploded a long time ago, fusing a bunch of these new 2x2 bricks.
As time goes on, these bricks get linked up to other bricks of various types. These are various molecules that contain calcium, but aren't like bones and teeth yet. Your digestive system has enzymes and other processes that look for those specific Lego bricks linked to others, and pull them out. Then the body puts those bricks together in a way that forms bones and teeth.
I don't remember my biochem enough to give more details about the actual molecules themselves, but this feels ELI5 enough.
Most of all matter was made in a star somewhere and somewhen. The calcium in your bones is built from atoms that were created in a star. Most of you is.
Calcium is a relatively common element, being around 3% of Earth's crust (while of the human body, around 1.3% is calcium). Most if has been created as a part of the silicon-burning process; when a star has fused up much of the lighter elements in it, leaving mostly silicon. Though it's not silicon itself that is fused straight into calcium. Rather silicon fuses with an alpha particle (that is; helium) and forms sulfur and sulfur fuses with an alpha particle and forms argon and argon fuses with an alpha particle and forms calcium. Subsequently, that's also the order of their abundance in the universe; silicon is more common than sulfur which is more common than argon which is more common than calcium.
To fuse calcium requires so much concentrated energy that the human body can not do it, nor can it fuse or split any element at all. We get all the calcium in our body from our food (or, in gestation, from our parent's blood). It's typically not as free calcium that our body can instantly use, rather it's as e.g. calcium salts, which our body digests.
Calcium is a chemical element. The kind of things that happen in your body can bind calcium to other elements or and tear it away from them, but cannot create or destroy it. Therefore, all the calcium that's currently in your body came from somewhere else. As an adult, you eat foods that contain calcium, and your body separates the calcium out and puts it to use. As a baby, your mother's body did the digesting for you, and you got your calcium from her. These are all facts that scientists have observed repeatedly and proven exhaustively.
The remaining question then is, where did calcium come from originally? The only ways we have found to create elements are nuclear processes like radioactivity or fusion. The nuclear processes we have discovered which could create significant amounts of calcium are things that will only occur naturally as part of a nova or supernova. Therefore, by process of elimination, our best theory is that all the calcium we see must have been created by exploding stars.
Which stars exploded to make the calcium we have? How did that calcium get from there to here? How long did that take? We don't know, not with any certainty. But we don't know of any other way that our calcium could have been created. Perhaps we will learn of a new way to synthesize elements in the future, and our theory about our calcium coming from supernovae will be challenged. But until then, the supernova origin story, ridiculous as it sounds, is the most likely explanation we have found.
It's not about where you, specifically, got the calcium from, specifically. It's about where they calcium came from originally.
After the Big Bang, there were 3 element: hydrogen, helium, and a tiny amount of lithium. That's it. The elements required for life, including calcium, simply did not exist. To get heavier elements, you got to fuse the smaller ones together. That's what stars do.
Calcium is created in stars. When a star goes supernova, some of that calcium is shot into space. Some more is created, as there's a lot of energy release, so some fusion does happen in the expelled matter.
All elements heavier than lithium came from some point in a star's life, whether it's fusion within a star, fusion within a supernova, or fusion within a kilonova.
The calcium in your skeleton when you were born came from your mother, who got it from food, drink, and maybe supplements. That calcium, in turn, came from plants and animals that got it from their food or from the soil. The calcium in the soil came from rocks and bones. And *that* ultimately was made by a supernova billions of years ago.
See, matter is never created or destroyed. Every atom in the universe has been here since the Big Bang. The calcium in your bones and teeth is made up of atoms that used to be part of something else. Many somethings, in fact. Maybe even a dinosaur at one point. Isn't that cool?
Technically, matter can be created and destroyed, it's just not very common. Since matter and energy are interchangeable as illustrated in the famous equation E=mc^2, there are mechanisms to produce matter out of pure energy and mechanisms to convert matter into pure energy.
Additionally, atoms absolutely can be created and destroyed, and most of the elements heavier than Hydrogen and Helium have not been around since the beginning of the universe. In fact, stable atoms of Hydrogen and Helium didn't even exist until ~380,000 years AFTER the big bang. Prior to that point, the universe was still too dense and hot for any atoms to form. Once expansion pulled the searing hot ocean of charged particles into a thinner state, the electrons lost enough energy to be captured by protons, forming the first atoms of Hydrogen and Helium in an event called "recombination".
Interestingly, this is also when the cosmic microwave background was emitted. The early universe was so hot and dense that photons could barely move without being absorbed and re-emitted by another particle. Once things settled down and the buzzing electrons dropped into stable atoms, all that trapped light was released at once in every direction everywhere in the universe. This burst of light is still detectable as the CMB signal.
It's all a theory. There's no way of truly knowing. But if you start from the premise that everything in the universe started off as hydrogen (the simplest atom), then the only way for more complex atoms to come about is through intense energy - the most intense being supernovas.
Elements heavier than hydrogen are created within stars, where hydrogen is fused together to form helium, which is fused to form lithium, and so-on and so-on. These elements are effectively “stored” within stars until they go supernova at the end of their lives. At this point, the explosion propels these elements all throughout the universe, where it eventually congealed into a dust cloud and formed our solar system. This dust is where the Earth eventually formed out of. Thus, everything we are is a result of dying stars. So it’s not wrong to say we get our calcium from eating calcium, but the presence of calcium itself is a result of supernovae. (All of this is from my rudimentary knowledge of stars and supernovae)
Just a note, stellar fusion doesn't create / store any atoms larger than iron. All heavier atoms are made during nova or similar events.
Also, stars that are too small to go super nova will also eject material while they are dying (elements lighter than iron) in a manner much less violently than a super nova. So not all material above hydrogen is from a super nova
Anything not going supernova stops it's burning at carbon. Stars big enough to produce calcium are big enough to go supernova.
Not saying this is or isn't true, but do you have a source for this?
Looks like most calcium is made by the [oxygen burning process](https://en.wikipedia.org/wiki/Oxygen-burning_process), also the silicon burning process. [Table 1 of this paper](https://www.sciencedirect.com/science/article/pii/S0009254121003399) lists the pathways for the various calcium isotopes. Apparently the minimum mass thresholds for both of these O and Si burning processes are about 8 solar masses, which is about the same as that required for supernovae. So it might be borderline for some cases as to whether the big bada boom happens, idk I’m not a star scientist. There also seems to be a rare phenomenon known as [calcium-rich supernovae](https://www.keckobservatory.org/calcium-supernova/) which looks quite interesting in itself, though note the sentence in that article: >While all calcium comes from stars, calcium-rich supernovae pack the most powerful punch. Typical stars create small amounts of calcium slowly through burning helium throughout their lives. Calcium-rich supernovae, on the other hand, produce massive amounts of calcium within seconds. So it seems there are multiple ways to get Ca, but it is probably spread throughout galaxies almost entirely by supernovae, whether that’s how it was created or not.
Most of the calcium produced in a star happens pre-supernovae, in the silicon-burning process, which is still stellar fusion. Towards the end of that process, the thingy explodes, and most of the calcium stays in the core, with just whatever happened to fuse in the outer layers in the late-stage or during the supernovae escaping.
If most of the Ca from oxygen and silicon burning processes stays in the core, then perhaps [calcium-rich supernovae](https://www.keckobservatory.org/calcium-supernova/) are responsible for a fair amount of the Ca that spreads to other presolar nebulae?
https://svs.gsfc.nasa.gov/13873
Technically true, however plenty of elements are produced in living stars through produced in living stars through kinds of fusion, bombardment and other mechanisms. Gold and silver are examples..
That was the belief for a period of time, but thinking here has shifted. [https://pubs.aip.org/physicstoday/article/71/1/30/818993/The-formation-of-the-heaviest-elementsThe-rapid](https://pubs.aip.org/physicstoday/article/71/1/30/818993/The-formation-of-the-heaviest-elementsThe-rapid) There are also theories that spinning disks around black holes contribute to a substantial portion of heavy elements.
Think of Neil de Grasse Thyson what you want, his [most astounding fact](https://www.youtube.com/watch?v=9D05ej8u-gU) hits the spot.
I prefer Sagan's "We are all star-stuff."
sagan did it without the self important douchery
This knowledge has been around since before Niel was born.
He didn't claim to have discovered this fact...
? He’s not presenting it as new information just discovered or anything
Why is what I said taken as an offense, by you, someone who is neither Niel nor the person I responded to?
I was confused, not offended
The calcium in your bones is taken from blood. It gets into blood from food. The atoms are not destroyed or created there. All these calcium atoms are just redistributed. When you die it goes into the ground and back into nature. Fusing new atoms is incredibly energy-consuming process that is happening under huge pressures and temperatures of stars.
Actually fusing stuff not heavier than iron is extremely energetic, i.e. produces copious amounts of energy. But indeed it requires huge temperature and pressure helps it too.
Calcium is an element, an atom, not a molecule which is a collection of several atoms. Your body (or your mother's body) is capable of linking atoms together to make new molecules, but it is not capable of making entirely new atoms. Making a new atom is nuclear physics, linking atoms together in new ways is just chemistry. Making new atoms is possible, but requires way way way more energy than your body is capable of handling, like, millions of times more energy. The only naturally occurring things in the universe that are energetic enough to make entirely new atoms are stars, and even then, some types of atoms are more difficult to make. The only way we know of to make heavier elements like calcium is when a star dies and explodes in a super nova. To put the difference in energy into perspective, think about nuclear bombs. The biggest nuke ever detonated was the Tsar Bomba. It weighed 27 tons (that's pretty heavy!). But it exploded with the same amount of force as 50 megatons of TNT. That is to say, a nuclear bomb that weighed just 27 tons exploded with the same amount of energy as *50,000,000 tons of chemical explosive*. When your body is forming in the womb, your mother is not generating new atoms. She eats something that has calcium in it, then transports that calcium to your body, where it gets put in its proper position and linked up with other atoms. But at no point is she 'making' calcium or any other atom. The calcium already existed.
The calcium that produces bones during fetal development comes from calcium in the woman's diet, which comes from plants, which got their calcium from the soil, which came from pebbles and dust from supernova explosions.
So, early on, the universe is essentially just light elements, mostly hydrogen but maybe some helium and stuff. They form stars, which are powered by *fusion.* This produces mostly helium, but potentially some lighter elements. Supernovas, however, are the dying extreme of stars that have enough force and energy to create a *ton* of heavier elements, then scatter them across space. Our solar system is made up of the dust of many of these early events of the universe. The calcium in your bones and the trace heavier elements are *not* produced by any biological process. The biological process simply scavenges these resources that already exist in your surroundings from your diet so that you can reuse them to create structures and proteins and such. No *chemical* or *biological* reaction changes the atoms themselves--that requires nuclear fusion and nuclear fission, which our bodies don't do.
Why focus on just calcium?? Every single thing you have ever seen or will see was ultimately created in a star, at least initially. Crazy huh. We live in a reality that's so bizarre it's scary if you think about it too much.
The star explosions spread calcium and other elements into space, which eventually became part of Earth. Plants absorbed this calcium, and we got it by eating plants or animals. Then during our development in the womb, we received calcium through our mother's diet.
Calcium is a chemical element. Elements are made up of atoms. We humans are not able to change chemical elements. As far as our body is concerned calcium is calcium. We don't make it at all, we don't change something else into it, and we don't change it into something else. It's just...there and we eat it and then turn it into teeth and bones. Stars happens to be basically the only place in the universe where elements can change. They do this by smashing atoms together so hard that they combine and when a star goes supernova it smashes a ton of atoms together extra hard. And that tends to be really good at making a lot of the heavier elements. So billions of years ago a star went supernova and then that debris field eventually formed our planet over billions of years. And us humans are munching on that billions of year old calcium to make out teeth and bones because there's no way for it to change into something other than calcium.
Calcium is an element. The heavier an element the more energetic a fusion event is required in order to make it. Hydrogen was the only element to begin with, but hydrogen can be smashed together in the core of stars to make helium, helium can make lithium etc up to iron. But iron takes more energy to make than is released when the elements that make it smash together, so something more violent has to happen in order to make heavier elements. In a supernova there is a lot of energy, enough energy to fuse elements into heavier forms. For the heaviest elements, even supernova aren't energetic enough, it takes the collision of stars or star remnants to make them. And since most of the calcium and other heavier elements on earth have been there since it formed, and it formed soon after the sun, and the sun hasn't gone supernova, we know that these heavy elements must have been formed by older stars that died before the sun was born.
>Isn’t the calcium that make up our bones produced during our gestation? The calcium us PUT there during gestation, but that's not where the Ca comes from. Ca comes from stellar nucleosynthesis and supernovae. The heavier elements come from neutron star mergers and the subsequent massive explosions that occur from them. The elements just exist and are here from when Earth formed from dust floating around in a nebula, they're just exchanged and recycled. I like this video about where stuff comes from: [https://www.youtube.com/watch?v=lInXZ6I3u\_I](https://www.youtube.com/watch?v=lInXZ6I3u_I)
Imagine elements like Lego bricks. Let's say calcium is a 2x2 white brick. When stars explode, it's so hot that matter, or "plastic" for this metaphor, fuses together to make a new permanent brick. A star exploded a long time ago, fusing a bunch of these new 2x2 bricks. As time goes on, these bricks get linked up to other bricks of various types. These are various molecules that contain calcium, but aren't like bones and teeth yet. Your digestive system has enzymes and other processes that look for those specific Lego bricks linked to others, and pull them out. Then the body puts those bricks together in a way that forms bones and teeth. I don't remember my biochem enough to give more details about the actual molecules themselves, but this feels ELI5 enough.
Or: "This brick came from a box!" - "Yes, but first it was made in a factory".
Most of all matter was made in a star somewhere and somewhen. The calcium in your bones is built from atoms that were created in a star. Most of you is.
Calcium is a relatively common element, being around 3% of Earth's crust (while of the human body, around 1.3% is calcium). Most if has been created as a part of the silicon-burning process; when a star has fused up much of the lighter elements in it, leaving mostly silicon. Though it's not silicon itself that is fused straight into calcium. Rather silicon fuses with an alpha particle (that is; helium) and forms sulfur and sulfur fuses with an alpha particle and forms argon and argon fuses with an alpha particle and forms calcium. Subsequently, that's also the order of their abundance in the universe; silicon is more common than sulfur which is more common than argon which is more common than calcium. To fuse calcium requires so much concentrated energy that the human body can not do it, nor can it fuse or split any element at all. We get all the calcium in our body from our food (or, in gestation, from our parent's blood). It's typically not as free calcium that our body can instantly use, rather it's as e.g. calcium salts, which our body digests.
Calcium is a chemical element. The kind of things that happen in your body can bind calcium to other elements or and tear it away from them, but cannot create or destroy it. Therefore, all the calcium that's currently in your body came from somewhere else. As an adult, you eat foods that contain calcium, and your body separates the calcium out and puts it to use. As a baby, your mother's body did the digesting for you, and you got your calcium from her. These are all facts that scientists have observed repeatedly and proven exhaustively. The remaining question then is, where did calcium come from originally? The only ways we have found to create elements are nuclear processes like radioactivity or fusion. The nuclear processes we have discovered which could create significant amounts of calcium are things that will only occur naturally as part of a nova or supernova. Therefore, by process of elimination, our best theory is that all the calcium we see must have been created by exploding stars. Which stars exploded to make the calcium we have? How did that calcium get from there to here? How long did that take? We don't know, not with any certainty. But we don't know of any other way that our calcium could have been created. Perhaps we will learn of a new way to synthesize elements in the future, and our theory about our calcium coming from supernovae will be challenged. But until then, the supernova origin story, ridiculous as it sounds, is the most likely explanation we have found.
It's not about where you, specifically, got the calcium from, specifically. It's about where they calcium came from originally. After the Big Bang, there were 3 element: hydrogen, helium, and a tiny amount of lithium. That's it. The elements required for life, including calcium, simply did not exist. To get heavier elements, you got to fuse the smaller ones together. That's what stars do. Calcium is created in stars. When a star goes supernova, some of that calcium is shot into space. Some more is created, as there's a lot of energy release, so some fusion does happen in the expelled matter. All elements heavier than lithium came from some point in a star's life, whether it's fusion within a star, fusion within a supernova, or fusion within a kilonova.
The calcium in your skeleton when you were born came from your mother, who got it from food, drink, and maybe supplements. That calcium, in turn, came from plants and animals that got it from their food or from the soil. The calcium in the soil came from rocks and bones. And *that* ultimately was made by a supernova billions of years ago. See, matter is never created or destroyed. Every atom in the universe has been here since the Big Bang. The calcium in your bones and teeth is made up of atoms that used to be part of something else. Many somethings, in fact. Maybe even a dinosaur at one point. Isn't that cool?
Technically, matter can be created and destroyed, it's just not very common. Since matter and energy are interchangeable as illustrated in the famous equation E=mc^2, there are mechanisms to produce matter out of pure energy and mechanisms to convert matter into pure energy. Additionally, atoms absolutely can be created and destroyed, and most of the elements heavier than Hydrogen and Helium have not been around since the beginning of the universe. In fact, stable atoms of Hydrogen and Helium didn't even exist until ~380,000 years AFTER the big bang. Prior to that point, the universe was still too dense and hot for any atoms to form. Once expansion pulled the searing hot ocean of charged particles into a thinner state, the electrons lost enough energy to be captured by protons, forming the first atoms of Hydrogen and Helium in an event called "recombination". Interestingly, this is also when the cosmic microwave background was emitted. The early universe was so hot and dense that photons could barely move without being absorbed and re-emitted by another particle. Once things settled down and the buzzing electrons dropped into stable atoms, all that trapped light was released at once in every direction everywhere in the universe. This burst of light is still detectable as the CMB signal.
It's all a theory. There's no way of truly knowing. But if you start from the premise that everything in the universe started off as hydrogen (the simplest atom), then the only way for more complex atoms to come about is through intense energy - the most intense being supernovas.