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Comic-style illustration of two meteorite impacts making a fiery red, orange, and yellow splash into an ocean. The sky above is dull yellow and cloudy.

4.3. What are the sources of life's building blocks outside the Earth?

A core learning question from the Astrobiology Learning Progressions

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5.1. How did life first emerge on Earth?

Grades K-2 or Adult Naive Learner

Have you ever seen a shooting star? People sometimes say to wish for something when a shooting star goes across the night sky. But did you know that a shooting star is actually not a star at all, but instead a piece of rock or ice landing on Earth from space? When a rock or a piece of ice falls onto Earth from space, it makes a glowing light in the sky at night. Sometimes, these things from space can even fall onto the ground and become part of our planet. Since living things need Earth to live and grow, there is a connection between these pieces of rock and ice in space and living things on Earth.

Portrait photo of Comic-style illustration of two meteorite impacts making a fiery red, orange, and yellow splash into an ocean. The sky above is dull yellow and cloudy.
Meteorite bombardment on the early Earth may have delivered building blocks needed for life to emerge.
NASA/Aaron Gronstal

Grades 3-5 or Adult Emerging Learner

Have you ever seen a shooting star? People sometimes say to wish for something when a shooting star goes across the night sky. But did you know that a shooting star is actually not a star at all, but instead a piece of rock or ice falling from space? When a rock or a piece of ice falls onto Earth from space, it makes a glowing light in the sky at night. These pieces of space stuff have been falling onto Earth for a really long time. Sometimes, these things from space can even fall onto the ground and get mixed in with the rocks and the dirt on our planet. Since living things need Earth to live and grow, there is a connection between these pieces of rock and ice in space and living things on Earth. So it’s important for scientists to study these pieces of stuff from space.

Portrait photo of Comic-style illustration of two meteorite impacts making a fiery red, orange, and yellow splash into an ocean. The sky above is dull yellow and cloudy.
Meteorite bombardment on the early Earth may have delivered building blocks needed for life to emerge.
NASA/Aaron Gronstal

Grades 6-8 or Adult Building Learner

When Earth and the other planets were forming in the solar nebula around 4.5 billion years ago, not all of the material ended up inside of the planets and all of the moons. There were a lot of smaller pieces leftover; from itty, bitty microscopic stuff to pieces of rock and ice that can be many miles across. These are things like the asteroids and the comets in our solar system.

Throughout Earth’s history these pieces of rock and ice have continued to rain down from space to Earth’s surface. We often use the word “meteoroid” to describe these pieces of space stuff that can fall onto Earth. Once in our atmosphere, the piece of rock or ice will burn up and produce a streak of light. It’s that light that we call a “meteor” or a “shooting star”. Sometimes the chunks of material are so big that they even hit the ground. In that case, we call it a “meteorite.”

Meteorites of all shapes and sizes have impacted Earth. Investigations of the material in meteorites have shown that the chemical elements needed for life can be found inside of these space rocks. These elements are known as the CHNOPS elements (carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur). In fact, scientists who do research on meteorites have even found that many of the types of molecules made up of CHNOPS elements that are used by living things on Earth are inside of those space rocks as well. These molecules include things like sugars and amino acids. Amino acids are the building blocks of proteins for all living things. Not only have we found the basic building blocks of life in meteorites, but we’ve also now used spacecraft to show that we can find them on the surfaces of asteroids and comets. We’ve even detected molecules made up of the CHNOPS elements within the dust of the interstellar medium – the material that exists between the stars in our galaxy.

All of this tells us that the CHNOPS elements and some of the basic building block molecules for life as we know it are actually quite common in the universe. Research on the connection between these materials from space and the presence of life on Earth will need to continue in order to better understand the history of life on Earth and to figure out if there could be other life somewhere out there.

Portrait photo of Comic-style illustration of two meteorite impacts making a fiery red, orange, and yellow splash into an ocean. The sky above is dull yellow and cloudy.
Meteorite bombardment on the early Earth may have delivered building blocks needed for life to emerge.
NASA/Aaron Gronstal

Grades 9-12 or Adult Sophisticated Learner

When Earth and the other planets were forming in the solar nebula around 4.5 billion years ago, not all of the material ended up inside of the planets and all of the moons. There were a lot of smaller pieces leftover; from itty, bitty microscopic stuff to pieces of rock and ice that can be many miles across. These are things like the asteroids and the comets in our solar system.

Throughout Earth’s history these pieces of rock and ice have continued to rain down from space to Earth’s surface. We often use the word “meteoroid” to describe these pieces of space stuff that can fall onto Earth. Once in our atmosphere, the piece of rock or ice will burn up and produce a streak of light. It’s that light that we call a “meteor” or a “shooting star”. Sometimes the chunks of material are so big that they even hit the ground. In that case, we call it a “meteorite”.

Meteorites of all shapes and sizes have impacted Earth. Investigations of the material in meteorites have shown that the chemical elements needed for life can be found inside of these space rocks. These elements are known as the CHNOPS elements (for carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur). In fact, scientists who do research on meteorites have even found that many of the types of molecules made up of CHNOPS elements that are used by living things on Earth are inside of those space rocks as well. These molecules include things like sugars and amino acids. Amino acids are the building blocks of proteins for all living things. Not only have we found the basic building blocks of life in meteorites, but we’ve also now used spacecraft to show that we can find them on the surfaces of asteroids and comets. We’ve even detected molecules made up of the CHNOPS elements within the dust of the interstellar medium (the material that exists between the stars in our galaxy).

The molecules that include carbon are often referred to as “organic molecules”. These include a lot of the molecules made up of CHNOPS elements that are important for life. Sometimes when we talk about these organic molecules that can come to Earth from space, we call the “exogenous” materials. That means that they came from somewhere else (as compared to something that is “endogenous”). Our research has told us that the early solar system had a lot more rocks and ice orbiting about that could crash into Earth and other worlds. Just as today, those materials likely had a lot of exogenous organic molecules on and in them. So, in the early history of Earth, there were a lot more meteorites falling to Earth and bringing along these exogenous organic molecules. We don’t yet know if these meteorites were an important source of materials for Earth life, but it seems likely that they could have brought a lot of the CHNOPS elements to Earth for living things to later use.

So we know that the CHNOPS elements and even some of the basic building block molecules for life as we know it are actually quite common in the universe. Research on the connection between these materials from space and the presence of life on Earth will need to continue in order to better understand the history of life on Earth and to figure out if there could be other life somewhere out there.

Portrait photo of Comic-style illustration of two meteorite impacts making a fiery red, orange, and yellow splash into an ocean. The sky above is dull yellow and cloudy.
Meteorite bombardment on the early Earth may have delivered building blocks needed for life to emerge.
NASA/Aaron Gronstal