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Comic-style illustration with a scene with an impact to planet Earth that strikes with a red fiery impact. In the center, multiple ball-and-stick molecular models float against a dark background, rendered in red, white, blue, and gray. On the right, the scene transitions to lush green vegetation, with flowers and vines.

4.1. Where do life's building blocks come from?

A core learning question from the Astrobiology Learning Progressions

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3.5. How can we tell if something is alive or not?

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4.2. What are the sources of life's building blocks within the Earth?

Grades K-2 or Adult Naive Learner

Your family may use a recipe to make dinner. This recipe explains how to put all of the ingredients together in order to make something healthy and delicious. Anything that is alive needs to have some kind of food that helps it to grow and move and live. All things that are alive may like different types of food, but it turns out that many of the ingredients for this food are the same.

Portrait photo of Comic-style illustration with a scene with an impact to planet Earth that strikes with a red fiery impact. In the center, multiple ball-and-stick molecular models float against a dark background, rendered in red, white, blue, and gray. On the right, the scene transitions to lush green vegetation, with flowers and vines.
Ancient meteorite bombardment may have delivered building blocks needed for life on early Earth, seeding our planet with the chemistry needed for life.
NASA/Aaron Gronstal

Grades 3-5 or Adult Emerging Learner

If you’ve ever helped to make dinner, you might have used a recipe that told you how to make the food. It tells you what ingredients to use and how to put them together to make something delicious. The food we eat gives us the energy to grow and move. Not all living things like the same type of food, but it turns out that most of the food for living things is made with the same ingredients.

There are living things all over Earth and even some things that live deep in the ground or up in the sky, so the ingredients needed for life must also be everywhere. The Earth is very old so the ingredients for living things must also have been around for many, many years. People who wonder if there is life somewhere other than Earth are investigating if the ingredients for living things are there or not.

Portrait photo of Comic-style illustration with a scene with an impact to planet Earth that strikes with a red fiery impact. In the center, multiple ball-and-stick molecular models float against a dark background, rendered in red, white, blue, and gray. On the right, the scene transitions to lush green vegetation, with flowers and vines.
Ancient meteorite bombardment may have delivered building blocks needed for life on early Earth, seeding our planet with the chemistry needed for life.
NASA/Aaron Gronstal

Grades 6-8 or Adult Building Learner

In order to better understand where life could exist beyond Earth, we need to consider what living things on Earth have in common. For instance, all living things on Earth need certain chemical elements in order to survive: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. We sometimes abbreviate this list and call it CHNOPS (which is pronounced like “sh-nops”). Similar to cooking, the CHNOPS elements are very much like the ingredients for a recipe: you need to have the right ingredients to make the recipe.

Where did the CHNOPS atoms come from? Well, just like most of the atoms in our bodies, most of the CHNOPS atoms on Earth came from space! Hydrogen is the most common element in the universe and it was formed along with most of the helium during the big bang. Meanwhile, elements like carbon, nitrogen, oxygen, phosphorus, and sulfur were made inside of stars, during the explosions of stars known as supernovae, and even when two really heavy stars (known as neutron stars) bumped into each other. When our solar system formed, a large amount of the CHNOPS elements were included in the Sun, the planets and other things in our solar system. Since other solar systems, with their own stars and planets, likely form in similar ways as our own, they also likely have a lot of the CHNOPS elements. This means that the basic ingredients for life as we know it are almost everywhere!

So why don’t we see alien life all over the place, even in our own solar system? Well, having the ingredients for a recipe is just one important part. The other important part is putting those ingredients together in the right way to make the recipe work. An important step in figuring out if there are other living things out there in the cosmos is finding the places where the CHNOPS elements (and other possible ingredients for life) have come together in the right way to make the recipe of life work.

Portrait photo of Comic-style illustration with a scene with an impact to planet Earth that strikes with a red fiery impact. In the center, multiple ball-and-stick molecular models float against a dark background, rendered in red, white, blue, and gray. On the right, the scene transitions to lush green vegetation, with flowers and vines.
Ancient meteorite bombardment may have delivered building blocks needed for life on early Earth, seeding our planet with the chemistry needed for life.
NASA/Aaron Gronstal

Grades 9-12 or Adult Sophisticated Learner

In order to better understand where life could exist beyond Earth, we need to consider what living things on Earth have in common. For instance, all living things on Earth need certain chemical elements in order to survive. If we look at all of the organisms on Earth, from the microbes living in hot springs to Orchids to Blue Whales, we see that the fundamental building blocks of life are all the same: all living things contain primarily carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. We sometimes abbreviate this list of life’s building blocks and call it CHNOPS (which is pronounced like “sh-nops”). Similar to cooking, the CHNOPS elements are very much like the ingredients for a recipe: you need to have the right ingredients to make the recipe.

Where did the CHNOPS atoms come from? Well, just like most of the atoms in our bodies, most of the CHNOPS atoms on Earth came from space! Hydrogen is the most common element in the universe and it was formed along with most of the helium during the Big Bang. Our current knowledge tells us that most of these atoms formed in just the first few minutes after the Big Bang happened. Other, larger atoms, including elements like carbon, nitrogen, oxygen, phosphorus, and sulfur (the rest of the CHNOPS elements), were made inside of stars, during the explosions of stars known as supernovae, and even when two neutron stars bumped into each other (this is called a neutron star merger). Events like supernovae cause space to become filled with dusts and gases containing all of these other elements, so when our solar system formed, a large amount of the CHNOPS elements were included in the Sun and the planets and other things in our solar system. Since other solar systems, with their own stars and planets, likely form in similar ways as our own, they also likely have a lot of the CHNOPS elements (and we can see this looking at the elements inside of other stars using something called spectroscopy). This means that the basic ingredients for life as we know it are almost everywhere!

So why don’t we see alien life all over the place, even in our own solar system? Well, having the ingredients for a recipe is just one important part. The other important part is putting those ingredients together in the right way to make the recipe work. An important step in figuring out if there are other living things out there in the cosmos is finding the places where the CHNOPS elements (and other possible ingredients for life) have come together in the right way to make the recipe of life work.

Portrait photo of Comic-style illustration with a scene with an impact to planet Earth that strikes with a red fiery impact. In the center, multiple ball-and-stick molecular models float against a dark background, rendered in red, white, blue, and gray. On the right, the scene transitions to lush green vegetation, with flowers and vines.
Ancient meteorite bombardment may have delivered building blocks needed for life on early Earth, seeding our planet with the chemistry needed for life.
NASA/Aaron Gronstal