Life is made of a few kinds of building blocks: amino acids (for proteins), sugars, fats, and the "letters" of DNA and RNA. Scientists have made many of these in the lab from simple ingredients, and found them in rocks that fell from space. How they first came together into a living cell is still being worked out.
Life didn't come from "nothing". It most likely came from chemistry: simple molecules that formed naturally on the early Earth and in space, then joined into longer chains that could copy themselves. Many steps have been shown in the lab; some haven't yet. "We don't know yet" is an honest answer. "So a god did it" isn't an answer at all.
"Life can't come from non-life." "The odds of a cell forming by chance are like a tornado building a jumbo jet." "Atheists believe everything came from nothing."
1. The ladder from atoms to cells
Click each step. The label shows how solid the evidence is.
- 1Atoms
- 2Simple molecules
- 3Building blocks
- 4Chains
- 5Self-copying RNA
- 6Bubbles
- 7First cells
2. Made in a jar: the Miller–Urey experiment
In 1953, Stanley Miller and Harold Urey filled a sealed flask with water and gases thought to be on the early Earth, and zapped them with sparks to imitate lightning. Within a week the water turned brown with amino acids, the building blocks of proteins. In 2008, scientists re-tested Miller's old sealed vials with modern equipment and found more than 20 different amino acids.1
Nobody "designed" those molecules. Energy plus simple ingredients made them. The early Earth had lightning, volcanoes, hot springs and ultraviolet light for hundreds of millions of years.
3. Delivered from space
You were right to think of space. Many of life's ingredients form on dust grains and inside asteroids, and they've been falling onto Earth ever since it formed.
| Space rock | What was found |
|---|---|
| Murchison meteorite (fell in Australia, 1969) | More than 70 kinds of amino acids, plus sugars and DNA/RNA bases. |
| Asteroid Ryugu (sample returned by Japan's Hayabusa2, 2020) | Uracil, one of the four "letters" of RNA.2 |
| Asteroid Bennu (sample returned by NASA's OSIRIS-REx, 2023) | 14 of the 20 amino acids life uses to build proteins, and all 5 of the bases used in DNA and RNA, plus the salty water they formed in.3 |
Because these samples were sealed and handled to avoid contamination, we know the molecules were made in space, not on Earth.
That idea is called panspermia. It's possible, and some microbes can survive a surprising amount of space exposure, but there's no evidence for it yet. And it only moves the question to another planet. What's well supported is that the ingredients come from space.
4. The "RNA world"
Today, DNA stores information and proteins do the work. Each needs the other, a chicken-and-egg problem. RNA can do both jobs: it stores information like DNA, and some RNA molecules (ribozymes) speed up chemical reactions like proteins. Even in your cells today, the core of the ribosome, the machine that builds every protein, is made of RNA. Many scientists think early life ran on RNA alone.
- In 2009, chemists showed that two RNA "letters" can form from simple chemicals in conditions like the early Earth.4
- Labs have evolved RNA molecules that can copy other RNA chains, though not yet a full copy of themselves.
- Fatty molecules like those in soap form hollow bubbles on their own in water. These can grow, divide, and trap RNA inside, much like a simple cell.
5. Where and when
- Water early. Tiny zircon crystals from Australia show Earth had liquid water about 4.4 billion years ago, soon after it formed.
- Life early. The oldest widely accepted fossils, layered microbe mats called stromatolites, are about 3.5 billion years old. Some evidence points older.
- Where? Leading ideas include hot springs on land that dry out and refill (concentrating chemicals), and deep-sea hydrothermal vents, which supply energy and minerals.
6. "A tornado in a junkyard"
The famous argument says a cell forming at random is like a tornado building a jumbo jet. But no scientist thinks a cell formed in one random step. Chemistry isn't random: atoms bond in predictable ways, and simple molecules assemble into bigger ones on their own, the way salt forms crystals. Each step builds on the last.
7. Watch it explained
Amino acids, sugars and DNA/RNA bases form naturally, in labs and in space. Life appeared on Earth within about a billion years of the planet forming.
Life is too complex to have come about naturally, so it must have been created.
Some critics, like chemist James Tour, argue that origin-of-life labs are far from making a living cell, that experiments rely on careful human control, and that the gap is bigger than popular accounts admit. That's partly fair: nobody has made life from scratch yet. The reply: a gap in our knowledge isn't evidence for any particular explanation. Every past gap (lightning, disease, the motion of planets) that was once filled with "God did it" turned out to have a natural cause. See how science works on the "god of the gaps".
Sources
- Johnson et al., "The Miller volcanic spark discharge experiment", Science 322 (2008).
- Oba et al., "Uracil in the carbonaceous asteroid (162173) Ryugu", Nature Communications 14 (2023).
- Glavin et al., Nature Astronomy (January 2025) and McCoy et al., Nature (January 2025); American Museum of Natural History, "Studies find life's building blocks in Bennu asteroid samples".
- Powner, Gerland & Sutherland, "Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions", Nature 459 (2009).