Where Did Life Come From? (feat. PBS Space Time and Eons!)

Summary

This script delves into the origin of life, challenging the notion that 1962 marked the most significant year for soup due to Warhol's art. Instead, it highlights 1952 and Stanley Miller's primordial soup experiment, which demonstrated how simple chemicals could form life's building blocks. The journey explores the 'RNA world' hypothesis, the central dogma of biology, and the potential role of deep-sea hydrothermal vents in the emergence of life. It concludes by emphasizing the inevitability of life's evolution and the ongoing quest to understand its true beginnings.

Takeaways

• 🎨 The year 1962 is often noted for Andy Warhol's pop art depiction of soup, but 1952 is highlighted for Stanley Miller's primordial soup experiment, which demonstrated how amino acids could form from simple chemicals, suggesting a pathway to life.
• 🔬 Miller's experiment provided evidence that non-living substances could potentially become the building blocks of life, supporting the 'prebiotic soup' theory proposed by earlier scientists.
• 🌏 The Earth's early conditions, including its formation around 4.5 billion years ago and the subsequent cooling that allowed for liquid water, set the stage for the emergence of life.
• ⏳ The earliest possible time life could have started on Earth is estimated to be around 4 billion years ago, at the beginning of the Archean Eon, following a period of heavy meteorite bombardment.
• 🔍 Fossil and chemical evidence suggest that early microbes existed by 3.7 billion years ago, marking the biosignature boundary and the onset of abiogenesis.
• 🤔 Defining what life is proves challenging, with even biologists struggling to pinpoint a universal definition, highlighting the complexity and diversity of life's characteristics.
• 🧬 Erwin Schrödinger proposed that life is a struggle against entropy, maintaining order and resisting decay, which is a key concept in understanding life's persistence and evolution.
• 🌱 Life is characterized by its ability to evolve, with the necessity of information-carrying molecules that can reproduce and diversify, aligning with the principles of natural selection.
• 🐣 The 'RNA world' hypothesis suggests that early life was based on RNA molecules capable of both storing genetic information and catalyzing chemical reactions, predating the DNA-protein world.
• 🔥 The central dogma of biology, which describes the flow of genetic information from DNA to RNA to protein, is a universal pathway shared by all life forms.
• 🌊 Deep-sea hydrothermal vents are theorized as potential birthplaces of life, offering a natural source of energy and environments conducive to the formation of simple cellular structures.
• 🔬 The journey from simple life forms to complex organisms involved significant evolutionary steps, including the transition from RNA to DNA and the development of protein-based cellular machinery.

Q & A

What year is often considered significant for the history of soup in the context of art?

1962 is often considered significant for the history of soup in the context of art, as it is the year when Andy Warhol released his soup-themed pop art.

What experiment by Stanley Miller in 1952 is considered a milestone in understanding the origins of life?

Stanley Miller's experiment in 1952 is considered a milestone because it demonstrated that amino acids, the building blocks of proteins, could be formed from simple chemicals under conditions that simulate the early Earth environment.

What is the concept of 'prebiotic soup' and when was it first theorized?

The concept of 'prebiotic soup' refers to a hypothetical set of conditions on the early Earth where organic molecules necessary for life could form. It was first theorized in the 1920s by two different scientists.

What did Charles Darwin speculate about the origins of life in 1871?

In 1871, Charles Darwin speculated that life may have originated from chemicals in some warm little pond, suggesting that life could have formed from a simple chemical 'soup'.

What is the 'primordial soup' theory and why was Miller's experiment significant in its context?

The 'primordial soup' theory posits that life originated from a pool of organic molecules in the early Earth. Miller's experiment was significant because it provided experimental evidence that such a soup could give rise to the building blocks of life.

What is the 'central dogma of biology' and why is it considered paradoxical?

The 'central dogma of biology' is the concept that genetic information flows from DNA to RNA to proteins. It is considered paradoxical because DNA replication requires proteins, and protein synthesis requires DNA, creating a chicken-and-egg dilemma.

What is the 'RNA world' hypothesis and how does it address the paradox of the central dogma?

The 'RNA world' hypothesis suggests that early life was based on RNA molecules that could both carry genetic information and catalyze chemical reactions. This hypothesis addresses the paradox by proposing that RNA could have preceded DNA and proteins, serving both as genetic material and as a catalyst for early life processes.

What is the role of deep-sea hydrothermal vents in the context of the origin of life?

Deep-sea hydrothermal vents are considered potential sites for the origin of life because they provide a natural source of energy and chemical gradients that could have driven the formation and maintenance of early life forms.

What is the 'last universal common ancestor' (LUCA) and why is it significant?

The 'last universal common ancestor' (LUCA) refers to the most recent organism from which all current life on Earth descends. It is significant because it represents a transition point from simple life forms to more complex organisms that exist today.

What is the 'biosignature boundary' and when did it occur?

The 'biosignature boundary' refers to the point in time when evidence of early microbial life is found, which occurred around 3.7 billion years ago. It marks the earliest known existence of life on Earth.

What is the definition of life proposed in the script, and what are the four rules that something must satisfy to be considered 'alive'?

The script proposes that life began the moment molecules of information started to reproduce and evolve by natural selection. The four rules are: 1) A living thing must work to avoid decay and disorder, 2) It must create a closed system or be made of cells, 3) It must have molecules that can carry information about how to build cell machinery, and 4) This information must evolve by natural selection.

Outlines

00:00

🍲 The Origins of Life and Primordial Soup

The video script begins with a discussion on the significance of soup in the history of life, referencing Andy Warhol's pop art and Stanley Miller's experiment that simulated the conditions thought to give rise to life on early Earth. It explores the concept of 'prebiotic soup' and Charles Darwin's musings on life's origins. The script emphasizes the complexity of life and introduces the quest for understanding the origin of life, including the timeline of Earth's formation and the earliest possible time life could have started, known as the habitability boundary. It also touches on abiogenesis, the process by which life arises naturally from non-living matter, and the challenges in defining what life is, suggesting that life is an activity rather than a state of being.

05:02

🧬 Defining Life and the Role of RNA

This paragraph delves into the complexities of defining life, highlighting the limitations of traditional biological definitions and proposing a new perspective that life is an active process of maintaining order against entropy. It discusses Erwin Schrödinger's view of life as a struggle against decay and the importance of molecules that carry information and evolve through natural selection. The script introduces the 'RNA world' hypothesis, suggesting that early life was based on RNA molecules capable of both storing genetic information and catalyzing chemical reactions. It explains the paradox of the chicken and egg problem between DNA and proteins and how an RNA-based life form could have bypassed this issue, setting the stage for the evolution of more complex life forms.

10:03

🌊 The Environment of Early Life and the RNA World

The final paragraph of the script explores the possible environments where life could have originated, dismissing the idea of panspermia and suggesting that life likely began on Earth. It discusses the role of deep-sea hydrothermal vents as potential sites for the emergence of the first life forms, providing both the necessary energy and the conditions for simple membrane-bound structures to form. The script describes how these early life forms could have harnessed the flow of hydrogen ions to maintain order and resist entropy, eventually leading to the transition from RNA to DNA and the development of more complex cellular machinery. It concludes by reflecting on the journey from the first simple life forms to the last universal common ancestor (LUCA) and acknowledges the ongoing nature of life's evolution, encouraging viewers to remain curious about the mysteries of life's origins.

Keywords

💡Primordial Soup

The 'primordial soup' refers to a hypothetical mixture of organic molecules that accumulated in the oceans of the early Earth, providing the necessary conditions for the emergence of life. In the video, it is mentioned in the context of Stanley Miller's experiment, which simulated the early Earth's conditions and resulted in the formation of amino acids, indicating that life's building blocks could have originated from such a 'soup'.

💡Amino Acids

Amino acids are organic compounds that are the building blocks of proteins. In the script, they are highlighted as essential ingredients for life, discovered by Stanley Miller in his primordial soup experiment. The presence of amino acids in this early 'soup' is a crucial step in the abiogenesis process, which is the natural process by which life arises from non-living matter.

💡Abiogenesis

Abiogenesis is the process by which living organisms arise from non-living matter, such as simple organic compounds. The video discusses this concept in the context of the transition from non-life to life, suggesting that life began when molecules started to reproduce and evolve through natural selection, which is a key part of the abiogenesis process.

💡Second Law of Thermodynamics

The second law of thermodynamics states that the total entropy of an isolated system can only increase over time. In the video, Erwin Schrödinger's perspective on life is mentioned, where he views life as a struggle against entropy, maintaining order and complexity within living organisms despite the natural tendency towards disorder.

💡RNA World Hypothesis

The RNA world hypothesis proposes that early in evolution, self-replicating RNA molecules preceded DNA and proteins, forming the basis for early life. The script discusses this hypothesis as a solution to the 'chicken and egg' problem of which came first, DNA or proteins, suggesting that RNA could have carried genetic information and catalyzed chemical reactions in the early stages of life.

💡Ribozymes

Ribozymes are RNA molecules that can catalyze chemical reactions, similar to the function of protein enzymes. The script mentions ribozymes as evidence supporting the RNA world hypothesis, noting that scientists have created ribozymes capable of self-replication, which is a fundamental aspect of life.

💡Natural Selection

Natural selection is the process by which organisms with traits that are better suited to their environment are more likely to survive and reproduce, leading to the spread of those traits in subsequent generations. The video describes natural selection as a critical component of life, necessary for evolution and the development of complexity in living organisms.

💡Hadean Eon

The Hadean Eon is the earliest part of Earth's history, spanning from about 4.6 billion to 4 billion years ago. The script refers to this period as the time when Earth formed and the conditions necessary for life began to emerge, setting the stage for the subsequent development of life.

💡Archean Eon

The Archean Eon is a geological eon that began about 4 billion years ago, following the Hadean Eon. In the video, it is identified as the earliest possible time when life could have started on Earth, marking the beginning of the 'habitability boundary'.

💡Biosignature Boundary

The biosignature boundary refers to the point in time when evidence of early microbial life is found, which is around 3.7 billion years ago. The script uses this term to denote the earliest known existence of life on Earth, providing a timeframe for the emergence of life post the habitability boundary.

💡Panspermia

Panspermia is the hypothesis that life exists throughout the Universe and can be transported between planets or planetary systems. The video briefly mentions panspermia as a theory for the origin of life on Earth, suggesting that life's building blocks could have been delivered via meteorites, but it emphasizes that this theory does not explain the origin of life itself.

Highlights

1962 marked a significant year in soup history with Andy Warhol's pop art, but 1952 was pivotal for 'primordial soup' experiments by Stanley Miller.

Miller's experiment simulated early Earth conditions, leading to the discovery of amino acids, crucial for life.

The 'prebiotic soup' theory dates back to the 1920s, suggesting life arose from a 'soup' of chemicals.

Charles Darwin speculated in 1871 that life may have originated in a 'warm little pond' of chemicals.

Miller's experiment provided evidence that non-living matter could become living, challenging the complexity of modern life's origins.

Life on Earth could not have started before its formation around 4.5 billion years ago.

The earliest possible time for life's origin on Earth was the Archean Eon, about 4 billion years ago.

Fossil and chemical evidence indicate the existence of early microbes by 3.7 billion years ago.

Abiogenesis, the transition from non-life to life, is a critical but elusive moment in Earth's history.

Defining 'life' is complex, as it's not just a state but a set of processes and characteristics.

Erwin Schrödinger viewed life as a struggle against entropy, maintaining order and complexity.

Life's definition includes the ability to avoid decay, create closed systems, carry information, and evolve.

The 'RNA world' hypothesis suggests that life began with RNA molecules carrying information and catalyzing reactions.

RNA's ability to both store information and catalyze reactions solves the chicken-and-egg problem of DNA and proteins.

Deep-sea hydrothermal vents are considered plausible sites for life's origin, providing necessary energy and environments.

The last universal common ancestor (LUCA) marks a significant milestone in the evolution from simple to complex life forms.

The journey from chemistry to biology and the emergence of life is an ongoing process, still unfolding today.

Darwin's theory of evolution not only explains the diversity of life but also its origins.

The quest for understanding life's origin is ongoing, with many gaps yet to be filled by scientific discovery.

Transcripts

Hey guys, Joe here.

Some people would argue the most important year in the history of soup was 1962, when

Andy Warhol released his soup-er soupy pop art.

But I think soup’s best year came a decade earlier, in 1952, when a scientist named Stanley

Miller first cooked up primordial soup.

Miller’s experiment took some simple chemicals, like those found on early Earth, bubbled them

up through a tube, zapped them with electricity, and after a few days, floating in this soup,

he found amino acids–the building blocks of proteins, and one of the essential ingredients

for life.

This idea–that life’s origins could be found in a puddle of chemicals–is an old

one.

In the 1920s, two different scientists theorized about life arising from what they called a

“prebiotic soup”.

And this soupy speculation even goes back (unsurprisingly) to Charles Darwin, who in

1871 wondered if life may have formed from chemicals “…in some warm little pond…”

What made Miller’s experiment so special was it gave us proof: regular non-life stuff

could become cool life stuff super-easily.

But… everything “living” we see today, even the most basic bacteria, is so complex,

built of such intricate machinery, it’s impossible to imagine they just popped into

existence out of some soup.

That’s because they didn’t.

We’re going to go on a journey in search of the origin of life, and along the way there

will be a few forks in the road, maybe a couple speedbumps, and we’re going to need help

from a couple friends.

We’ll come to see that Miller’s primordial soup isn’t exactly how this story began.

But the FIRST question we should ask isn’t how life started, it’s when.

Life on Earth couldn’t exist before Earth existed, and it formed around four and a half

billion years ago, at the dawn of the Hadean Era/Eon.

Soon after that, another planet collided with the young Earth, melted the entire crust,

and created the moon in the process.

After the crust cooled, there was even some liquid water… at least for a little while.

Because for the next couple hundred million years, Earth was showered with hundreds of

massive space rocks.

The oceans boiled away, the crust melted again, and Earth was basically no place for life…

until things settled down about 4 billion years ago, at the dawn of the Archean Eon.

This is the earliest possible time that life could have started on Earth, the beginning

of what we call the habitability boundary.

And fossil and chemical evidence tell us that early microbes existed by 3.7 billion years

ago, what’s known as the biosignature boundary.

At some moment in here, non-life became life: we call this abiogenesis.

Now, I don’t have a time machine.

As far as I know, no one does.

Therefore we can’t go back and find that exact moment.

But if we could, what would we look for?

This brings us to the next big question on this journey… what is life?

You’d think biology would have a good definition for life, the thing it studies.

But as a biologist I can tell you this is much harder than it sounds.

In one chapter of biologist JBS Haldane’s 1949 book What Is Life? he literally writes

“I am not going to answer this question.”

Life is a board game, a delicious breakfast cereal, and a highway?

According to the dictionary, it’s the time between birth and death.

But none of these definitions really help us.

I think we might be asking the wrong question, because life isn’t a thing that things have,

life is what living things do.

In school, many people learn a checklist for the characteristics a thing must have in order

to be “alive”: MRS GREN.

But this list came from looking at life as we know it today.

Life at the very beginning was probably much simpler.

A physicist, Erwin Schrödinger, looked at all these things that life does and saw something

only a physicist would see:

According to the second law of thermodynamics,  . But inside of living cells there’s a

huge amount of order and complexity.

In 1944, Schrödinger defined life as a struggle against entropy– the persistent resistance

of decay, the preservation of DISequilibrium.

Since then we're learned a lot more about entropy, and it may be that the rise of complexity

is as inevitable as its decay.

That sounds pretty good.

Life creates these little closed systems where it works to keep things nice and ordered.

But this definition still leaves out one important thing: Living things evolve.

Inside the very first living things must have been molecules–chains of atoms–that carried

information–instructions for building things or codes for doing stuff.

Those molecules must have copied and made more of themselves, some a little different

than the others.

And a few of those codes and instructions must have been better at doing whatever they

did, so they made even more of themselves.

What we’re describing is evolution by natural selection, Darwin’s famous idea, and for

life to move forward, it must have been there from the beginning.

Life is a product of evolution.

With all this in mind, maybe we’re finally able to come up with a better definition:

Life began the moment that molecules of information started to reproduce and evolve by natural

selection.

And now that we have a definition we can make some rules for what something

has to do to be “alive”.

1.

A living thing must work to avoid decay and disorder

2.

To do that, a living thing has to create a closed system, or be made of cells

3.

They have some molecule that can carry information about how to build cell machinery

4.

This information must evolve by natural selection Sounds pretty good, but rules are one thing.

The ultimate question is how would this actually happen?

Let’s take these rules one by one.

What would it require for these things to arise?

And–most importantly–how likely are each of these steps based on what we know from

good ‘ol real, actual, hard science?!

Today, no matter where we look on the tree of life, most cell machinery is made of protein–

chains of folded amino acids.

When modern cells make proteins, they copy genes from DNA into RNA and then use that

RNA as a blueprint for making the proteins.

We call this universal pathway the central dogma of biology,

because it sounds really cool, and because it’s something that all life shares.

But there’s a paradox hidden in here–a puzzle.

It’s a chicken and egg problem!

DNA needs proteins to make more of itself.

And cells need DNA and the instructions it holds to make proteins.

So which came first?

We can solve this paradox in a pretty simple way.

Just get rid of DNA and protein in the earliest days of life, and let RNA do everything.

RNA is the molecular cousin of DNA.

It contains the same four-letter alphabet code as DNA, only T is replaced by a similar

molecule, U.

And instead of two strings in a helix, RNA is usually found in just one string.

RNA is special, because in addition to carrying information in that 4-letter code, it can

fold up into interesting shapes and actually do stuff.

The same way that protein enzymes can do all kinds of chemical reactions, RNA enzymes–called

ribozymes–can work life’s machinery too.

It’s now thought that life began in an RNA world.

Before DNA became a more permanent form of storage, different RNA chains could have carried

information and been the machines for all of life’s important chemistry.

Unfortunately, the RNA-only world went extinct more than 3 billion years ago, but we can

make these RNA enzymes today.

Scientists have constructed ribozymes that can copy themselves, just like DNA gets copied.

And those copies occasionally have errors or changes, so RNA can evolve too.

If you need more proof you can find it right inside your cells.

The ribosome, the massive structure that stitches amino acids into protein, is mostly RNA.

We also find nucleotides, the single molecular units of RNA, inside a bunch of other molecules

our cells need for metabolism.

This all makes sense only if the earliest days of living chemistry were dominated by

RNA.

And it solves our chicken and egg problem.

The RNA world takes care of two of our four rules: A molecule that can carry information

(3), and that can evolve (4).

To find answers for the other two, we need to ask one more question: Where did life begin?

There’s been a lot of theories about where life came from, but they boil down to these:

Either life arose on Earth, or life arose somewhere else and was brought here.

It’s well-known that space is full of the chemical building blocks of life, from amino

acids to DNA and RNA letters...

...buried inside meteorites like this one that fell on Australia in 1969.

It shows the chemistry that makes biological molecules can happen pretty much anywhere.

But the idea that life was delivered to Earth on space rocks, which goes by the awesome

name panspermia… well there’s just no proof it ever happened, and it doesn’t really

explain the origin of life anyway.

It just moves it somewhere else.

Life probably started here.

No… zoom out a little.

We know early Earth had plenty of chemical ingredients, but the problem with that old

idea of primordial soup is that soup can’t do anything on its own–those chemicals can’t

react without outside energy.

We get a hint of where this primordial energy came from by looking (again) at our own cells.

Instead of lightning, or heat energy, our cells pile up a bunch of hydrogen ions (protons)

on one side of a wall, let ‘em flow downhill, and use this like a water wheel to push on

cellular machinery (and make things like ATP in the mitochondria)

We burn food to keep our hydrogen pump going, but the first life forms wouldn’t have been

able to do this, because tacos hadn’t been invented yet.

Instead, they would have needed some natural source, and they could have found it at the

bottom of the ocean.

Deep-sea hydrothermal vents are covered in microscopic little pockets, which could have

served as molds for the first cells.

Molecules with one oily water-hating end and one water-loving end have a neat habit of

forming bubbles and sheets all on their own

and there were plenty of these in the chemical soup near deep sea vents, ready to give rise

to the first cell membranes.

These vents also create natural streams of hydrogen ions near those little pockets in

the rock.

Imagine an early life form sitting there, wrapped in its little membrane bubble,

with a free source of energy flowing by, powering all the work it takes to create ordered life

and resist entropy.

But this would have been the absolute simplest form that life could take.

For this life form to become life that looks like what we know today, a lot more stuff

had to happen: it had to switch from storing its genetic information in RNA and started

using DNA.

Instead of using RNA and ribozymes to run all its cellular machinery, it had to start

stitching amino acids into proteins.

This opened up new possibilities for making and storing energy that let early life become

free-living and more complex.

One of these complex life forms is the ancestor of everything alive today, the last universal

common ancestor, or LUCA.

This is the end of our journey, searching for the origin of life on Earth.

A lot has happened since.

This story is based on things we’ve actually seen, not just on what’s possible.

We’ve figured out when life could have started.

We’ve come up with rules for what life is.

We’ve found clues inside our own cells that explain how the first life satisfied these

rules, and where that life might have started.

The only question we haven’t answered is why, but that’s not really a question for

science, is it?

There’s still quite a few gaps to fill in this story, and if you’re looking for a

nice, neat answer for how life started, you’re probably not going to find it.

Life is just a thing that happens.

It’s still happening today, and it will evolve and continue as long as there’s a

place it can happen.

Darwin didn’t know it when he wondered about that warm little pond, full of chemicals,

giving rise to life, but his theory of how things change and adapt turned out to be so

powerful it encompasses life not just in its endless forms, but also in its first ones.

Stay curious.

Wow.

That was a LOT.

This is probably the deepest story I’ve ever done on this channel, and it’s one

that involves some of the science I actually used to do, so this was a lot of fun for me.

I hope you enjoyed it too.

But this is only part of the story of how life began.

What happened before, to made Earth a place where life could happen?

And what happened after chemistry became biology, what life form lives at the bottom of our

tree of life?

For those answers, go check out these videos from our friends at PBS Space Time and Eons.