Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

Miller Urey Experiment

Miller Urey Experiment

Many consider discussions on how life originated on earth to be purely hypothetical, but in 1952 two American chemists--Harold C. Urey and Stanley Miller--set out to test the time's most prominent 'origin of life on earth' theory. Here, we will learn about the Miller-Urey experiment!

  • First, we will look at the definition of the Miller-Urey experiment.
  • Then, we will talk about the results of the Miller-Urey experiment.
  • After, we will explore the significance of the Miller-Urey experiment.

The Definition of the Miller-Urey Experiment

Let's start by looking at the definition of the Miller-Urey experiment.

The Miller-Urey Experiment is a key test tube earth experiment which kick-started evidence-based research into the origin of life on earth.

The Miller-Urey experiment was an experiment that tested the Oparin-Haldane Hypothesis which was, at the time, a highly regarded theory for the evolution of life on earth through chemical evolution.

What was the Oparin-Haldane Hypothesis?

The Oparin-Haldane Hypothesis suggested life emerged from a series of step by step reactions between inorganic matter driven by a large energy input. These reactions initially produced the 'building blocks' of life (e.g., amino acids and nucleotides), then more and more complex molecules until primitive life forms arose.

Miller and Urey set out to demonstrate that organic molecules could be produced from the simple inorganic molecules present in the primordial soup as the Oparin-Haldane Hypothesis proposed.

We now refer to their experiments as the Miller-Urey Experiment and credit the scientists with uncovering the first significant evidence for the origin of life through chemical evolution.

The Oparin-Haldane Hypothesis--note that this point is important--described life emerging in the oceans and under methane-rich reducing atmospheric conditions. So, these were the conditions that Miller and Urey attempted to mimic.

Reducing atmosphere: An oxygen-deprived atmosphere where oxidation can't occur, or occurs at very low levels.

Oxidizing atmosphere: An oxygen-rich atmosphere where molecules in the form of released gases and surface material are oxidized to a higher state.

Miller and Urey attempted to recreate the reducing primordial atmospheric conditions laid out by Oparin and Haldane (Figure 1) by combining four gases in an enclosed environment:

  1. Water vapor

  2. Methane

  3. Ammonia

  4. Molecular hydrogen

Miller-Urey Experiment Apparatus StudySmarter

Figure 1. Diagram of the Miller-Urey experiment. Source: Wikimedia Commons.

The pair of scientists then stimulated their faux atmosphere with electrical pules to simulate energy provided by lightning, UV rays or hydrothermal vents and left the experiment running to see if the building blocks for life would form.

Miller-Urey Experiment Results

After running for a week, the liquid simulating the ocean inside their apparatus turned a brownish-black color.

Miller and Urey's analysis of the solution showed complex stepwise chemical reactions had occurred forming simple organic molecules, including amino acids - proving organic molecules could form under the conditions laid out in the Oparin-Haldane hypothesis.

Before these findings, scientists had thought the building blocks of life like amino acids could only be produced by life, inside an organism.

With this, the Miller-Urey Experiment produced the first evidence that organic molecules could be spontaneously produced from only inorganic molecules, suggesting Oparin's primordial soup could have existed at some point in Earth's ancient history.

The Miller-Urey experiment did not, however, fully back up the Oparin-Haldane hypothesis as it only tested the initial stages of chemical evolution, and didn't dive deeper into the role of coacervates and membrane formation.

Miller-Urey Experiment Debunked

The Miller-Urey experiment was modelled on, and recreated conditions laid out under the Oparin-Haldane Hypothesis. Primarily recreating the reducing atmospheric conditions the previous pair stipulated was crucial for the formation of early life.

Though recent geochemical analysis of the earth's primordial atmosphere paints a different picture...

Scientists now think the earth's primordial atmosphere was composed mainly of carbon dioxide and nitrogen: an atmospheric makeup very different from the heavy ammonia and methane atmosphere that Miller and Urey recreated.

These two gases that were featured in their initial experiment are now thought to have been found in a very low concentration if they were present at all!

The Miller-Urey Experiment Undergoes Further Testing

In 1983, Miller attempted to recreate his experiment using the updated mixture of gases - but failed to produce much more than a few amino acids.

More recently American chemists have again repeated the famous Miller-Urey Experiment using the more accurate gaseous mixtures.

Whilst their experiments returned similarly poor amino acid turn out, they noticed nitrates forming in the product. These nitrates were able to break down amino acids as quickly as they formed, yet in the conditions of primordial earth iron and carbonate minerals would have reacted with these nitrates before they had the chance to do so.

Adding these crucial chemicals to the mix produces a solution that, whilst not as complex as the initial findings of the Miller-Urey Experiment, is abundant in amino acids.

These findings have renewed hope that continued experiments will further pin down likely hypotheses, scenarios, and conditions for the origin of life on earth.

Debunking the Miller-Urey Experiment: Chemicals from Space

Whilst the Miller-Urey Experiment proved organic matter can be produced from inorganic matter alone, some scientists are not convinced this is strong enough evidence for the origin of life through chemical evolution alone. The Miller-Urey Experiment failed to produce all the building blocks needed for life - some complex nucleotides have yet to be produced even in subsequent experiments.

The competition's answer to how these more complex building blocks came about is: matter from space. Many scientists believe these complex nucleotides could have been brought to earth through meteorite collisions, and from there evolved into the life that occupies our planet today. However, it is important to note this is just one of the many origin of life theories.

Miller-Urey Experiment Conclusion

The Miller-Urey Experiment was a test tube earth experiment, recreating the reducing primordial atmospheric conditions thought to have been present during the origin of life on earth.

The Miller Urey experiment set out to provide evidence for the Oparin-Haldane hypothesis and has provided evidence for the occurrence of the first simple steps of chemical evolution. Giving validity to Darwin's puddle and Oparin's primordial soup theories.

Perhaps more importantly, however, is the field of pre-biotic chemical experiments which followed. Thanks to Miller and Urey we now know more than previously thought possible about potential ways life could have originated.

The significance of the Miller-Urey Experiment

Before Miller and Urey performed their famous experiments, ideas such as Darwin's puddle of chemistry and life and Oparin's primordial soup were nothing more than speculation.

Miller and Urey devised a way to put some ideas about the origin of life to the test. Their experiment has also prompted a wide variety of research and similar experiments showing similar chemical evolution under a wide range of conditions and subject to different energy sources.

The main component of all living organisms is organic compounds. Organic compounds are complex molecules with carbon at the center. Prior to the findings of the Miller-Urey Experiment it was thought these complex biotic chemicals could only be produced by life forms.

The Miller-Urey Experiment, however, was a pivotal moment in the history of research into the origin of life on earth - as Miller and Urey provided the first evidence that organic molecules could come from inorganic molecules. With their experiments, a whole new field of chemistry, known as pre-biotic chemistry was born.

More recent investigations into the apparatus used by Miller and Urey have added further validity to their experiment. In the 1950s when their famous experiment was carried out glass beakers were the gold standard. But glass is made of silicates, and this could have leeched into the experiment affecting the results.

Scientists have since recreated the Miller-Urey experiment in glass beakers and Teflon alternatives. Teflon is not chemically reactive, unlike glass. These experiments showed more complex molecules forming with the use of glass beakers. At first glance, this would appear to cast further doubt on the applicability of the Miller-Urey experiment. However, the silicates contained in glass are very similar to the silicates present in the earth's rock. These scientists, therefore, suggest that primordial rock acted as a catalyst for the origin of life through chemical evolution.3

Miller Urey Experiment - Key takeaways

  • The Miller-Urey Experiment was a revolutionary experiment which birthed the field of pre-biotic chemistry.
  • Miller and Urey provided the first evidence that organic molecules could come from inorganic molecules.
  • This evidence of simple chemical evolution transformed ideas from the likes of Darwin and Oparin from speculation to respectable scientific hypotheses.
  • Whilst the reducing atmosphere mimicked by the Miller-Urey is no longer thought to be reflective of primordial earth, their experiments paved the way for further experimentation with different conditions and energy inputs.

References

  1. Kara Rogers, Abiogenesis, Encyclopedia Britannica, 2022.
  2. Tony Hyman et al, In Retrospect: The Origin of Life, Nature, 2021.
  3. Jason Arunn Murugesu, Glass flask catalysed famous Miller-Urey origin-of-life experiment, New Scientist, 2021.
  4. Douglas Fox, Primordial Soup's On: Scientists Repeat Evolution's Most Famous Experiment, Scientific American, 2007.

Frequently Asked Questions about Miller Urey Experiment

Miller and Urey’s experiments set out to test whether life could have emerged from the chemical evolution of simple molecules in the primordial soup, as laid out by the Oparin-Haldane Hypothesis. 

The Miller Urey experiment was the first to demonstrate how organic molecules could have formed under the reducing primordial atmospheric conditions laid out in the Oparin-Haldane hypothesis.

The Miller Urey experiment was a test tube earth experiment, recreating the reducing primordial atmospheric conditions thought to have been present during the origin of life on earth. The Miller Urey experiment set out to provide evidence for the Oparin-Haldane hypothesis.

The Miller Urey experiment is significant because it provided the first evidence that organic molecules could be spontaneously produced from only inorganic molecules. Whist the conditions recreated in this experiment are no longer likely to be accurate, the Miller-Urey paved the way for future origin of life on earth experiments.

The Miller Urey experiment consisted of an enclosed environment containg heater water and various other compounds thought to have been present in the primordial soup according to the Oparin-Haldane hypothesis. Electrical currents were applied to the experiment and after a week simple organic molecules were found in the enclosed space. 

Final Miller Urey Experiment Quiz

Question

What did the Miller-Urey experiment provide evidence for?

Show answer

Answer

The Miller-Urey Experiment provided the first evidence that organic molecules could come from inorganic molecules which is important in research on the origin of life on Earth.

Show question

Question

Prior to the findings of the Miller-Urey Experiment it was thought that ____ could only be produced by life forms. 

Show answer

Answer

organic compounds

Show question

Question


In 1953 American chemists Harold C. Urey and Stanley Miller set out to test the Oparin-Haldane Hypothesis. What did the Oparin-Haldane Hypothesis say about the evolution of life on earth?


Show answer

Answer

The Oparin-Haldane Hypothesis suggested life emerged from a series of step by step reactions between inorganic matter driven by a large energy input. These reactions initially produced the 'building blocks' of life (e.g., amino acids and nucleotides), then more and more complex molecules until primitive life forms arose.

Show question

Question

___ is defined as an oxygen-deprived atmosphere where oxidation can't occur, or occurs at very low levels. 

Show answer

Answer

reducing atmosphere

Show question

Question

___ is defined as an oxygen-rich atmosphere where molecules in the form of released gases and surface material are oxidized to a higher state. 

Show answer

Answer

oxidizing atmosphere

Show question

Question

How did Miller and Urey recreate the reducing primordial atmospheric conditions laid out by Oparin and Haldene?

Show answer

Answer

Miller and Urey attempted to recreate the reducing primordial atmospheric conditions laid out by Oparin and Haldane by combining water vapor, methane, ammonia, and molecular hydrogen in an enclosed environment. 

Then, they stimulated their faux atmosphere with electrical pules to simulate energy provided by lightning, UV rays or hydrothermal vents and left the experiment running to see if the building blocks for life would form. 

Show question

Question

The results of Miller and Urey's experiment ___ that

organic molecules could form under the conditions laid out in the Oparin-Haldane hypothesis. 

Show answer

Answer

proved

Show question

Question

The Miller-Urey experiment was modelled on, and recreated conditions laid out under what hypothesis?

Show answer

Answer

The Oparin-Haldane Hypothesis

Show question

Question

How has the Miller-Urey experiment been challenged in recent years?

Show answer

Answer

The Miller-Urey experiment was modelled on, and recreated conditions laid out under the Oparin-Haldane Hypothesis, primarily recreating the reducing atmospheric conditions the previous pair stipulated was crucial for the formation of early life. Scientists now think the earth's primordial atmosphere was comprised mainly of carbon dioxide and nitrogen, which is very different from the atmospheric makeup (with heavy ammonia and methane) that Miller and Urey recreated. 

Show question

Question

What happened when other scientists attempted to recreate the Miller-Urey experiment using more accurate gaseous mixtures?

Show answer

Answer

Whilst their experiments similarly produced amino acid, they noticed nitrates forming in the product. These nitrates were able to break down amino acids as quickly as they formed, yet in the conditions of primordial earth, iron and carbonate minerals would have reacted with these nitrates before they had the chance to do so.

Show question

Question

Why are some scientists unconvinced that life originated from chemical evolution alone?

Show answer

Answer

The Miller-Urey Experiment failed to produce all the building blocks needed for life - some complex nucleotides have yet to be produced even in subsequent experiments. 

Show question

Question

The Miller-Urey experiment led to the birth of what field in chemistry?

Show answer

Answer

Pre-biotic chemistry

Show question

Question

What could be inferred from the formation of complex molecules when the Miller-Urey experiment was performed in glass beakers as opposed to gold?

Show answer

Answer

The silicates contained in glass are very similar to the silicates present in the earth's rock. These scientists, therefore, suggest that primordial rock acted as a catalyst for the origin of life through chemical evolution.

Show question

Question

The Oparin-Haldane Hypothesis, crucially, described life emerging in the oceans and under what conditions?

Show answer

Answer

methane-rich reducing atmospheric conditions

Show question

Question

Describe the results of the Miller-Urey experiment. 

Show answer

Answer

After running for a week, the liquid simulating the ocean inside their apparatus turned a brownish-black color. Miller and Urey's analysis of the solution showed complex stepwise chemical reactions had occurred forming simple organic molecules, including amino acids - proving organic molecules could form under the conditions laid out in the Oparin-Haldane hypothesis. 

Show question

More about Miller Urey Experiment
60%

of the users don't pass the Miller Urey Experiment quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Sign up to highlight and take notes. It’s 100% free.