Why does life exist? Follow the energy

The following is an excerpt from “Why Do We Exist?: The Nine Realms of Universe that Make You Possible” by Hakeem Oluseyi.

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Life is concentrated energy.

A single year of sunshine delivers more energy to Earth’s surface than all of Earth’s known fossil fuel reserves combined. Yet, for the time being, we primarily power our modern society using petroleum, coal, and gas.

Fossil fuels possess remarkably high energy concentrations. Take a gallon of gasoline. This meager volume of liquid possesses the capacity to propel a vehicle weighing over two tons a distance greater than twenty miles at a considerable speed.

Fossil fuels, such as gasoline, derive their name from their origin as the remnants of ancient life, including wetland forests transformed into coal and algae and zooplankton transformed into petroleum. It is truly striking to consider that the force driving much of our modern society is rooted in the energy stored in past life-forms.

But why does life exist at all? Unsurprisingly, I am not the first scientist to ponder this question or seriously consider its answer. There is a theory that explains the emergence of life as a natural consequence of molecules self-organizing to absorb and then dissipate heat energy. In other words, life spontaneously comes into existence specifically to facilitate the process of energy leaving matter—the idea of minimization mentioned at the conclusion of the previous chapter.

The origin of life on Earth remains a topic of much scientific debate and speculation. But there are some elements of the process that we have deciphered. What is certain is that Earth’s geological conditions in its early history constrained how, when, and where life began on this, our home. Once formed, life became a geological force, modifying the planet and altering itself in response, creating a never-ending process of change, adaptation, and the emergence of greater and greater biological complexity. (You might think I’m talking about us here, with all the recent and well-founded alarm over climate change and fancy words like “Anthropocene” coming into the lexicon, but really, I’m talking about any form of life that can modify the planet’s chemistry. For example, cyanobacteria perform photosynthesis, modifying atmospheric and ocean chemistry—and they ain’t us.)

But we’re getting ahead of ourselves. Before organic evolution, there was molecular evolution. As we have learned, stars synthesize most elements. Some elements are created in the process of core fusion. Some are made in envelopes of old stars. Some are created when stars explode. And some are created when the cores of dead binary stars collide—all the gold you’re wearing, for example, comes from this process. However, none of these processes produces the complex molecules on which life depends.

Nature excels at forming simple molecules consisting of one or two types of atoms. You are already familiar with many of these abundant, small molecules. Nitrogen (N2), oxygen (O2), and hydrogen (H2) gases are common molecules consisting of only one type of atom. Substances like water (H2O), carbon dioxide (CO2), methane (CH4), and ammonia (NH3) are common molecules consisting of two types of atoms.

The types of molecules life uses, such as amino acids for building proteins and nucleotide bases for RNA and DNA, contain many more atoms and are much more complex. Due to their complexity, they are harder to build, easier to destroy, and much rarer than nature’s abundant, simple molecules. For life to take hold, there must be an evolutionary process that uses simple molecules as the starting material and, over time, builds more complex molecules.

This type of molecular evolution proceeds by adding energy to small molecules, breaking them apart, and then allowing them to recombine spontaneously into more complex forms until a self-replicating molecule is formed. In a famous set of experiments, scientists in the 1950s filled a flask with water, methane, and hydrogen and then added energy through an electrical spark. They didn’t produce self-replicating molecules, but they did produce eleven of the twenty amino acids on which Earth life is based.

In the decades since the 1950s, origin-of-life experiments have become considerably more sophisticated. In 2018, researchers in Ontario, Canada, created a machine called the Planet Simulator, which mimicked conditions on early Earth. After running the experiment for only a couple of months, the researchers discovered that it had spontaneously produced “protocells” and RNA strands. Their work confirmed the basic idea behind the RNA world hypothesis, a leading theory for the development of early life. They concluded that life is “probably a relatively frequent process in the universe.”

If this is true, what are the minimum requirements for basic life? And what constitutes basic life?

First, we need a self-contained vessel to form a cell membrane, which creates an enclosed volume separate from the rest of existence. A cell’s membrane is what allows life to stay organized and become more complex, even though nature tends to favor disorder. The second law of thermodynamics says that, over time, things naturally break down and become more random. But inside a living cell, the opposite happens: The cell builds structures, carries out precise chemical reactions, and maintains order. This isn’t magic; it results from the membrane’s ability to control what happens inside.

The membrane surrounds the cell’s internal environment, creating a space where it can organize itself without interference from the outside. It acts like a manager, ensuring that the right molecules are directed to their intended locations while maintaining balance between different cellular components. Inside, the cell is filled with tiny compartments, each with its own function, and the membrane helps control the movement of energy and materials between them. This allows the cell to store energy, build complex molecules, and conduct reactions in a controlled manner, rather than allowing everything to mix randomly.

Because of this controlled organization, the cell isn’t overwhelmed by entropy. Instead, it channels energy into creating order, keeping itself running smoothly, and even evolving into more sophisticated forms over time.

For Earth life, cell membranes are formed from a type of fat molecule known as a lipid. Lipids form abundantly in nature and have a remarkable property: When placed in water, they spontaneously self-organize into spherical structures—essentially primitive membranes. These kinds of lipid-based protocells are exactly what the Planet Simulator experiment produced. The fact that they formed so readily in a simulated early Earth environment suggests that protocells may not be rare or difficult to generate. On the contrary, they might be one of the easiest and most natural steps toward life.

Speaking of water, a liquid solvent is needed because it provides a flexible, dynamic environment where molecules can move, interact, and undergo the chemical reactions necessary for life. A solid would lock molecules in place, preventing them from mixing and reacting, while a gas would be too chaotic, with molecules moving too fast and too far apart to sustain stable interactions. (And you can forget about plasma—it’s way too crazy in there!) A liquid, however, strikes the right balance: It allows molecules to dissolve, come together, and react in a controlled yet adaptable way.

Water, the liquid solvent of life on Earth, is particularly good at this because it can dissolve a wide range of substances, making it easy for cells to transport nutrients, remove waste, and maintain a stable internal chemistry. It also helps proteins and other biological molecules fold into the right shapes to function properly, and it supports the flow of energy that cells need to survive. Water is also abundant not only on Earth but throughout our solar system and the universe.

Hypothetically, other liquids could support life in different conditions. For example, some scientists speculate that methane, which is liquid at extremely cold temperatures, might serve as a solvent for alien life. Laboratory experiments have shown that many of the molecules utilized by life are stable in more exotic liquids—including ammonia and even sulfuric acid (the Alien alien, with acid for blood, could be real!)—so water isn’t strictly necessary, but a liquid is. Life needs a medium where molecules can move and interact in a way that allows complexity to emerge and sustain itself.

After a vessel and a liquid, the next two ingredients required are large, complex genetic messenger molecules like RNA and DNA, and proteins necessary for structure and metabolism.

The Planet Simulator experiment showed that these molecules can form spontaneously in nature, and not just on Earth. As of 2022, all five nucleotide bases that form RNA and DNA have been found in meteorites. As for proteins, we’ve known since the 1950s that the amino acids used by proteins can be spontaneously produced.

Other experiments provide even more compelling data. In 2022, researchers analyzing samples from the asteroid Ryugu discovered more than twenty types of amino acids. This finding was particularly exciting because the Hayabusa2 probe collected pristine subsurface asteroid material. Before landing on the asteroid, Hayabusa2 deployed a small explosive device called the small carry-on impactor. This device launched a copper projectile into Ryugu’s surface at high speed, creating a crater and exposing fresh subsurface material.

Following this operation, the spacecraft descended to the newly formed crater area. Hayabusa2 then used its sampling horn to collect the excavated subsurface material. During this process, a five-gram metal bullet was fired into the surface, stirring up debris that was funneled into the spacecraft’s sample container. This method ensured that pristine material from beneath Ryugu’s weathered outer layer was captured for analysis back on Earth, untainted by Earth’s atmosphere or microorganisms, providing a pure glimpse into the asteroid’s composition.

In early 2025, scientists made a remarkable discovery in the samples returned by NASA’s OSIRISREx mission from the asteroid Bennu. They identified thirty-three different amino acids, including fourteen of the twenty amino acids life uses to build proteins. This finding is extraordinary because it represents the most diverse array of amino acids ever found in extraterrestrial material. The Bennu samples were also found to be rich in carbon, nitrogen, and ammonia, suggesting that asteroids might have played a crucial role in supplying the raw materials for life on our planet.

And now the search is tightening closer to home. In September 2025, NASA announced what it called “the clearest sign yet” of possible life on Mars, based on chemical fingerprints preserved in the ancient mudstones of Jezero Crater. The Perseverance rover discovered that organics and reactive minerals, such as iron and sulfides, are bound together in ways that, on Earth, typically trace back to microbial activity. While non-biological explanations remain on the table, the discovery raises the possibility that simple life not only arose on our neighboring planet but left behind signatures we can still read billions of years later. At the moment, this is just circumstantial evidence, similar to circumstantial evidence we’ve found on our planet that hints at Earth’s earliest life. But in the case of the Martian samples, the circumstantial evidence is stronger, and it could be conclusive if we can safely return the samples to Earth for detailed study.

These findings don’t just tell us about the past; they also hint at the potential for life elsewhere in the universe. At a minimum, the universe appears to be brimming with protocells, amino acids, and RNA.

The process of transforming nonliving matter into self-replicating cells is one thing. Going from these cells to an advanced technological civilization like ours is another matter entirely. And here is where Earth’s rare conditions come into play. To consider how humans came to exist, we must again indulge the absurd and escape some of our normal deception. Virtually every single animal on Earth and most fungi require oxygen for aerobic respiration. This is a metabolic process that takes glucose and oxygen and converts them into water, carbon dioxide, and energy in the form of ATP molecule chemical bonds (these bonds provide energy for other cellular functions, such as those that help our muscles contract, our nervous systems transmit signals, and our cells make other cells).

Likewise, all nonparasitic plants and algae require sunshine for photosynthesis, which happens to run counter to respiration: Here, plant cells take water, carbon dioxide, and energy (in the form of sunlight) and convert these into glucose and oxygen.

These two complementary processes are vital to the vast majority of life on Earth.

But when life on Earth was just getting started, neither oxygenic photosynthesis nor aerobic respiration had developed. Those early cells were simple and rudimentary, and couldn’t deal with oxygen, which is highly reactive (just think of what oxygen does to iron). In fact, oxygen was lethal to early life-forms on Earth. Complex Earth life, which requires oxygen and which produces it in abundance, had to evolve. And as luck would have it, it did evolve right here on planet Earth.

Why? You might think it’s because of our abundant water. But that’s not enough. Lots of bodies in our solar system contain water. At least two moons of Jupiter—Ganymede and Europa—have even more water than Earth.

What makes Earth special is that our liquid water is bathed in sunlight.

So far, we have identified nine other ocean worlds in our solar system: Europa, Ganymede, Callisto, Titan, Enceladus, Pluto, Triton, Mimas, and Ceres. The oceans of these worlds are covered by miles of ice, rock, or a completely opaque atmosphere—and sometimes all three. Only one of these boasts abundant surface liquids of any sort: the Saturnian moon Titan. But Titan’s atmosphere is so thick that 90 percent of the light that reaches the tops of its clouds is absorbed before making it to the surface. Titan is ten times farther from the Sun than Earth, which means that the tops of Titan’s clouds receive only 1 percent of the sunlight that Earth does, which in turn means that Titan’s surface receives only 0.1 percent of Earth’s surface irradiance. It’s dark down there! If indigenous conscious beings are walking (or rolling or swimming or flying) around on Titan, they don’t even know that stars exist!

These conditions are typical not only of our planetary system but of most others as well. They are predominant. In recent years, we have discovered approximately six thousand planets around other stars, plus the thirtyeight spherical bodies within our solar system. This sample shows that atmospheres usually occur in one of two basic configurations: superthick or virtually absent. Earth is the outlier.

Excerpted from Why Do We Exist? copyright © 2026 by Hakeem Oluseyi with Nils Johnson-Shelton. Used by permission of Ballantine Books an imprint and division of Penguin Random House LLC, New York. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.

Meet the Writer

Hakeem Oluseyi

About Hakeem Oluseyi

Dr. Hakeem Oluseyi is an astrophysicist and author of “Why Do We Exist? The Nine Realms of the Universe That Make You Possible.“