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"Comic-style illustration showing organic chain molecules washing from land into body of water, depicted by grey arrows, illustrating prebiotic chemistry and polymerization reactions.

5.1. How did life first emerge on Earth?

A core learning question from the Astrobiology Learning Progressions

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5.2. How did the first cells arise?

Grades K-2 or Adult Naive Learner

Have you ever had a mystery to solve? Like a time when you knew something happened, but you didn’t really know how? Maybe you felt like you needed to find some clues to figure out what happened. That’s how scientists feel about figuring out how life got going here on Earth long ago. If you have a mystery and are curious, you start looking for clues. Scientists are doing that right now. They may not figure it all out before you are a grown up. When you get older maybe you could help find clues to this mystery as well. What kinds of clues do you think would be helpful in learning about things that happened long ago?

Portrait photo of "Comic-style illustration showing organic chain molecules washing from land into body of water, depicted by grey arrows, illustrating prebiotic chemistry and polymerization reactions.

Grades 3-5 or Adult Emerging Learner

The Earth is really old. It’s older than any grownups you know, it’s older than human civilization, and it’s older than the time when the dinosaurs were alive. But, as old as Earth is, we’ve found evidence that tells us that living things have been around on Earth for almost as long as our planet has been here.

Life started on Earth so long ago that it’s hard for us to know exactly how it started. But there are scientists out there who are collecting information from old rocks, running experiments in laboratories, and using computer programs to test their ideas in order to learn more about the origin of life on Earth. It’s a pretty big mystery to try to uncover and we might never know for sure how life started, but we’re getting closer and closer to understanding how it could have happened.

Portrait photo of "Comic-style illustration showing organic chain molecules washing from land into body of water, depicted by grey arrows, illustrating prebiotic chemistry and polymerization reactions.

Grades 6-8 or Adult Building Learner

The Earth is really old. Using the tools of science, we have learned that Earth is about 4.5 billion years old. As old as Earth is, we’ve found evidence that tells us that living things have been around on Earth for almost as long as our planet has been here. We have evidence that tells us that life may have been on Earth as far back as about 4 billion years ago.

Life started on Earth so long ago that it’s hard for us to know exactly how it started. But there are scientists out there who are trying to figure that out. They include people who study the fossils of ancient bacteria or look for other signs of ancient life in old rocks. There are also people who are running experiments in laboratories to see how the basic building blocks of life can come together to make living things. And there are people who use computer programs to test our ideas about how life might have started.

Uncovering the origin of life on Earth is a pretty big mystery to try to solve. We might never actually know for sure how life started, but we’re getting closer and closer to understanding how it could have happened here on Earth and possibly on other worlds as well.

Portrait photo of "Comic-style illustration showing organic chain molecules washing from land into body of water, depicted by grey arrows, illustrating prebiotic chemistry and polymerization reactions.

Grades 9-12 or Adult Sophisticated Learner

One of the greatest mysteries about life on our planet is when and how it first started. Life appears to have been here for a very long time. Using the tools of science, we have learned that Earth is about 4.5 billion years old. And, as old as Earth is, we’ve found evidence that tells us that living things have been around on Earth for almost as long as our planet has been here. We have evidence that tells us that life may have been on Earth as far back as about 4 billion years ago and maybe even before that.

Life started on Earth so long ago that it’s hard for us to know exactly how it started. But there are scientists out there who are trying to figure that out. They include field scientists who study the fossils of ancient bacteria or look for other signs of ancient life in old rocks. For instance, they sometimes will look at the isotopes of elements like carbon that are trapped in old rocks to see if they imply biological activity. If they find such evidence, they can then also use other information from the rocks to figure out what kind of environment was available for the potential living things that were around when the rock formed. There are also scientists who are running experiments in laboratories to see how the basic building blocks of life can come together to make living things. For example, some lab experiments can be set up to figure out what conditions would be necessary for cell membranes to form without life. It turns out that some molecules can come together to make pockets just like cells under the right conditions. Outside of studying clues that we can find in the rocks and running experiments in labs, we can also use computer programs to test our ideas about how life might have started. All of these kinds of research projects have helped us to learn a lot more about how life might have come about on our planet.

Many scientists agree that the earliest life would have needed a good bit of water, the fundamental CHNOPS elements present to make organic molecules, and some way to concentrate simple organic molecules (since that would be necessary to make more complex molecules for biological processes). This can happen in tidal zones around the ocean, in little droplets of water that get sprayed into the atmosphere from ocean waves, where hydrothermal vents form on the ocean floor, or maybe even in small ponds or lakes when they dry up. It would also have been necessary to bring these molecules together in just the right way to make some chemical reactions more likely to occur. It turns out that some minerals, including pyrite (made of iron and sulfur) and many clays, are really good at orienting molecules in ways that causes them to react with each other. Life as we know it is based on cells, so an environment where life emerges would also need naturally-made containers with an inside and outside. It turns out that little enclosures with lipid membranes, just like cells, can form without life (also called “abiotically”). Depending on the chemistry of the fluid involved, these non-living cells can form automatically.

Environmental niches being investigated as potential places for the origin of life on Earth include surface waters such as lakes and ponds, sea ice, hydrothermal vents, tide pools, and hot springs. All of these areas currently have living things thriving in them, many of which are considered to be extremophiles. Investigations on the genetics of known organisms on Earth has suggested that the earliest life might have been thermophilic (adapted to hotter environments), which has caused a lot of people to suspect that hydrothermal systems might be important for the formation of life. As we learn more about how life on Earth may have started, it helps us to better understand the places we should first look at on other worlds in our solar system and beyond if we want to see if alien life exists. For instance, the possibility for hydrothermal vents to be active and possible sites of living processes in the oceans of Europa and Enceladus make these two moons really important places for us to study.

Uncovering the origin of life on Earth is a pretty big mystery to try to solve. We might never actually know for sure how life started, but we’re getting closer and closer to understanding how it could have happened here on Earth and possibly on other worlds as well. Perhaps the emergence of life on a world isn’t just something that happens on it, but rather to it. Some people suspect that the development of life is a natural process that occurs for many worlds in the Universe, but we can’t test that idea or figure out how common life may be until we’ve first discovered whether or not we’re alone.

Portrait photo of "Comic-style illustration showing organic chain molecules washing from land into body of water, depicted by grey arrows, illustrating prebiotic chemistry and polymerization reactions.