Date: January 3, 2012

Title: Encore:Humans Are Star Stuff

Podcaster: Carolyn Collins Petersen

Links: Loch Ness Productions

This podcast originally aired on February 10, 2009:

Description: Most of the atoms in our body once existed inside a star. This podcast traces our journey from star stuff to the stuff of life – a process that took billions of years of evolution to complete.

Bio: Carolyn Collins Petersen is a science writer and show producer for Loch Ness Productions, a company that creates astronomy documentaries and other materials. She works with planetariums, science centers, and observatories on products that explain astronomy and space science to the public. Her most recent projects were the Griffith Observatory astronomy exhibits in Los Angeles and the California’s Altered State climate change exhibits for San Francisco’s California Academy of Sciences. She has co-authored several astronomy books, written many astronomy articles, and is currently working on a new documentary show for fulldome theaters and a vodcast series for MIT’s Haystack Observatory.


Hi, I’m Carolyn Collins Petersen, TheSpacewriter.
When we think about traveling through space, we usually imagine going to Mars or colonizing the Moon, or even moving at warp speed out to the stars. It’s like we’re destined to go out there and find new places to explore because, as a species on planet Earth, we’ve never actually been very far out to space.

Well, that’s not quite true. We HAVE been in space before. Just not in our present forms.

The elements in our bodies, and all the other life forms on our planet, and the elements that make up the Sun and all the places in our solar system – they were all created long before we were even a dim glow in a cloud of gas and dust.

So, where did those elements come from?

Let’s start with hydrogen – it’s the most plentiful. And it’s what stars are made of. All the hydrogen in the universe was created during the Big Bang – the event that began the universe almost 14 billion years ago.

Hydrogen combines easily with other elements. When it joins with oxygen — it makes H2O – water – which we know is essential for life. In fact, WE are mostly water. Our skin, organs, muscles, bones, and nerves basically give the water a place to hang out.

The other elements in our bodies – the calcium in our bones, the iron in our blood, the carbon molecules that are the underpinnings of proteins and amino acids – those were all cooked up inside stars that died long before the solar system ever formed.

So, in a sense, we – and everything we see around us – are made up of the ashes of old, dead stars.

Here’s another way to think of us: we are the end product of a long-running interstellar chemistry experiment.

So, how does that experiment work? You start with stars. They cook up elements as they “burn” fuel to generate heat and light.
Now, because of the way stars live and die, the elements produced in this process of “stellar nucleosynthesis” end up in clouds of interstellar gas and dust. As stars go through their lives, they cast off mass through their stellar winds. The solar wind from our own Sun is a good example of this “mass loss.”

The older stars get the more mass they blow off. And, when they come to the ends of their lives, many stars wind up surrounded by clouds of material they’ve ejected earlier.

As a sun-like star begins to die, it lights up its envelope of gas and dust. This creates what astronomers call a planetary nebula. Our Sun could end up as one of these ghostly objects in about five billion years.

This planetary-nebula process spreads elements like carbon, and nitrogen, and oxygen out to space. But, what about the heavier elements like magnesium and silicon, iron, nickel, gold, and uranium? Those are created in stars much more massive than the Sun as they age and die.

Now, the nuclear furnace in an aging massive star doesn’t shut down quietly, like it does in the core of a planetary-nebula star. Instead, it continues to chug away, turning out heavier and heavier elements. This goes on until it tries to fuse together atoms of iron. And, fusing iron takes way more energy than the star has available.

When THAT happens, the whole furnace just shuts down, and things get very busy, very fast.

First, the star’s outer layers collapse in on its super-dense core. Then, they bounce back, causing a huge supernova explosion that creates even more heavy elements and hurls everything out to space at tremendous speeds. This process of element creation is called “explosive nucleosynthesis.”

So, that’s how the chemical elements for life are created in stars — and how space gets populated with clouds that are rich in hydrogen gas and mixtures of elements from planetary nebula formation and supernova explosions.

Now, those dense clouds slowly, slowly collapse to form new stars. And, once a star is born, the leftovers then go on to make asteroids and planetesimals: the seeds of planets. We know about this because it happened here, and we’ve seen it occurring in other places–like the Orion Nebula.

The clouds also contain molecules of what scientists call “pre-biotic” materials – things like amino acids, which form proteins. There are also sugars and other compounds that eventually combine to make life possible. And life, as biologists and chemists are finding out, takes advantage of whatever seed material there is to form, grow, and evolve.

Still, it’s not as simple as having elements and compounds floating around in space and then – poof! Life happens! It’s way more complex than that. And, how it happened on Earth is a complicated science story that researchers are still figuring out.

I think it’s pretty amazing to know that we and all other life forms are the end products of a cosmic process that began back at the Big Bang. It has continued across 13.7 billion years of star formation, galaxy evolution, and the creation of our own solar system.

The story of life’s evolution from its chemical precursors in space is the focus of a fascinating science called astrobiology. If you’d like to know more about it and how life expands from clouds of star-stuff, surf on over to and read the 365 Days of Astronomy page about Star Stuff.

Remember that chemically – and in every way that chemistry makes possible – we really ARE star stuff.

(Note: a very special thanks to Roger Cappallo, Ph.D., staff scientist at MIT’s Haystack Observatory; Joshua Roth, Ph.D, (Winchester High School physics department),and Sara Seager, Ph.D., Ellen Swallow Richards Associate Professor of Planetary Science and Associate Professor of Physics at MIT for graciously advising me on writing of the script for this episode of 365 Days of Astronomy.)

End of podcast:

365 Days of Astronomy
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