Two questions that get mixed up
One of the most common objections to evolution goes like this: “Evolution cannot even explain how life started.”
The reply is simple and honest. It does not try to.
Evolution is a theory about how living populations change over generations. It starts with things that already reproduce, already pass on traits, and already make small copying errors. Once you have those three ingredients, evolution follows.
How that first reproducing system came to exist is a different question. It has its own field, usually called abiogenesis or origin-of-life research, with its own experiments and its own arguments.
Mixing the two is like blaming a doctor who studies how children grow for not knowing how the first human ancestor appeared. Both are real questions. They are not the same question.
Why admitting the gap costs nothing
Some people expect this admission to be a win against evolution. It is not, and it helps to see why.
Think about fire. Physicists and chemists understand burning very well. They can tell you about oxygen, fuel, heat, and the chemical reactions involved. Now suppose a house burns down and nobody ever works out what started it. A dropped match? A faulty wire? Lightning?
The unknown cause does not damage the chemistry of combustion. The two are separate questions, tested by separate evidence.
Evolution is in the same position. It rests on fossils in dated rock layers, on DNA comparisons between living species, and on change observed directly in bacteria, insects, and finches. None of that evidence depends on knowing how the first cell formed.
What we do know: the timeline
Some parts of this story are not in doubt.
- The Earth is about 4.54 billion years old, measured mainly from meteorites using radioactive clocks.
- The earliest widely accepted evidence of life is roughly 3.5 billion years old. Microbial structures and chemical signatures from the 3.48-billion-year-old Dresser Formation in the Pilbara region of Western Australia are among the best examples.
- Some researchers argue for older traces. In 2016, a team reported cone-shaped structures in 3.7-billion-year-old rocks at Isua in Greenland and read them as fossil microbial mats. Other scientists re-examined the same rocks and concluded the shapes were made by heat and pressure, with no life involved. That argument is still open, which is why the safer statement is “about 3.5 billion years”.
So life appeared on a young planet, in a window of a few hundred million years. That is the target any origin-of-life explanation has to hit.
The Miller-Urey experiment, 1953
In 1953, at the University of Chicago, a graduate student named Stanley Miller worked with the chemist Harold Urey on a famous experiment.
Miller sealed water and a mixture of gases into glass apparatus. He heated the water to make vapour and fired electric sparks through the gas, standing in for lightning. Then he let the mixture circulate for days.
The water turned brown. When Miller analysed it, he found amino acids, the units that link together to build proteins.
That result mattered because it broke an old assumption. Many chemists had believed that the molecules of life could only be made by living things. Miller showed that simple chemistry, energy, and time could make them with no organism involved.
What the experiment did not show
Miller did not make life. He made building blocks. A pile of bricks is not a house.
There is also a fair criticism. Miller used a gas mixture that scientists in the 1950s thought matched the early Earth. Later research suggested the early atmosphere was probably less rich in those gases than he assumed.
The follow-up nobody expected
Miller kept his sample vials. After he died in 2007, a team including his former student Jeffrey Bada went through the stored extracts. Some came from a second apparatus Miller had built and never fully analysed. The team ran the old samples through modern equipment, far more sensitive than anything available in 1953.
Their results appeared in the journal Science in 2008, in a paper led by Adam Johnson. The vials from the setup that mimicked a steamy volcanic eruption held more than twenty amino acids. That is a wider range than the classic 1953 run produced. Volcanic settings, with lightning and steam, look like plausible chemical workshops on the early Earth.
Building blocks arriving from space
On 28 September 1969, a meteorite broke up over Murchison, in Victoria, Australia. More than 100 kilograms of it were collected, quickly, before it sat around gathering Earth chemistry.
The Murchison meteorite is packed with organic molecules. Researchers have identified a large set of amino acids in it, and most of them are not used by life on Earth at all. That mismatch is important: it shows the molecules are not contamination from soil or fingers. Isotope measurements confirm an extraterrestrial origin.
The lesson is not that life came from space. It is that the chemistry needed for life forms readily in ordinary places in the solar system, without any biology to help. The building blocks are common.
The RNA world idea
Modern life uses a division of labour. DNA stores information. Proteins do the chemical work. But DNA needs proteins to be copied, and proteins need DNA to be built.
That looks like a chicken-and-egg problem. The RNA world hypothesis offers a way around it.
RNA is a cousin of DNA. Like DNA, it can store information in a sequence of chemical letters. But in the early 1980s, Thomas Cech and Sidney Altman found that some RNA molecules do a second job as well. They act as catalysts, which means they speed up chemical reactions the way proteins do. RNAs that do this are called ribozymes. The discovery won a Nobel Prize in 1989.
So RNA can do both jobs, at least partly. If early life used RNA for storage and for chemistry, the chicken-and-egg problem softens. DNA and proteins could take over the two roles later, each doing its job better.
There is a striking piece of supporting evidence inside you right now. The ribosome, the machine every living cell uses to build proteins, forms the crucial chemical bond using RNA, not protein. Biologists often call that a molecular fossil of an earlier world.
The idea is not finished, though. Making RNA from scratch under early-Earth conditions is chemically difficult, and researchers still argue about how it happened.
Hydrothermal vents
Another line of work looks at the deep sea floor.
Hydrothermal vents are places where water heated by rock pours out into cold ocean. Some are the scalding black smokers. Others, like the Lost City field discovered in the Atlantic in 2000, are cooler and alkaline, and they build tall chimneys of porous mineral.
Those porous chimneys are interesting for three reasons. They provide tiny compartments. They provide a steady energy supply. And they build up chemical differences across thin mineral walls, a little like the differences living cells use to make energy today.
Laboratory groups build reactors to test whether that setting can drive the needed reactions. Some results are encouraging. Other researchers argue the gradients in real vents do not behave the way the hypothesis requires. This is normal, healthy scientific disagreement, and it is not settled.
What is still unknown
It would be dishonest to end this page with a tidy answer. Here is the real state of play.
- Nobody has made a self-copying system from simple chemicals in a laboratory, start to finish.
- There is no agreement on where it happened: warm pools, volcanic springs, deep-sea vents, or ice.
- There is no agreement on what came first: information, metabolism, or membranes.
- The record is hard to read, because the Earth destroyed nearly all rock from that era.
Origin-of-life research has real experiments, real chemistry and real progress. It does not have a finished answer.
What science does and does not claim
Being clear about the boundaries helps everyone.
Science claims that life on Earth shares common ancestry, and that populations change through inheritance, variation, and selection. The evidence for that is strong and comes from many independent directions.
Science does not currently claim to know how the first living system arose. Researchers have serious hypotheses under test, and they say openly that the question is open.
Science also does not claim that an unsolved question means “therefore nothing natural could have done it”. An unsolved problem is a place to keep working, not a conclusion.
Many people hold religious beliefs about why there is life at all. That is a different kind of question from how the chemistry worked, and a page like this one has nothing to say about it. Plenty of scientists who study evolution are religious, and plenty are not.
The short version
Evolution explains how life changes. It does not explain how life began, and it never promised to.
The origin of life is a genuinely open problem, with a fascinating pile of partial answers: amino acids from sparks in 1953, amino acids in a meteorite that fell in 1969, RNA molecules that can act as catalysts, and vents that make gradients on the sea floor.
Saying “we do not know yet” about that first step takes nothing away from the evidence for what came after. If you want to see that evidence, start with what is evolution and then read the evidence section.