17: The Building Blocks of Life

It’s been a while, but we’re finally back to the main story of this podcast. The globe-trotting miniseries we just finished was meant to be just a summer palate cleanser. Then, everything in my life was put on pause as I moved from France to Michigan and started a brand-new job. When I finally had enough personal time again, I knew I had to finish the mini-series first before returning to the main course her.

In short, it’s good to be back, and I hope you feel the same way. A few months have passed since Episode 16, so let’s take a step back, brush the dust off previous sessions and see what we’ve learned.

Part 1: The Story So Far

We’re in the home stretch of Season 1, which covers Earth’s first chapter, called the Hadean. The Hadean begins with Earth’s formation 4.6 billion years ago, and ends with Earth’s earliest rocks 4 billion years ago. In more practical terms, the Hadean covers January 1st to February 15th on the Earth Calendar. 

The Hadean in the Earth Calendar

In Episodes 4-7, we saw the birth of Earth as trillions of asteroids clumped together in the early solar system. A few of these asteroids are still floating around, which tell us Earth’s birthday of 4.6 billion years. The early solar system was a violent arena of destruction. Most worlds were swallowed by the sun or collided into each other. In this crossfire, Earth quickly grew from a sand grain to a real planet, forming an iron-rich core, a thick mantle of green olivine crystals, covered with a thin crust on top, our home. 

Earth was lucky, and dodged most of its’ planetary siblings, but not all. In Episodes 8 and 9, we met Theia, a rogue world the size of Mars, which crashed into the infant Earth. The fallout from this titanic collision formed our closest neighbor, the Moon. The early moon would have looked as large as your fist in the night sky, cooling from an angry red eye to a bright white golf ball as it drifted farther away. The man in the moon has not yet appeared on this show. 

All this information comes from asteroids and moon rocks, which have escaped Earth’s constant recycling of wind and water. There are no Hadean rocks left on Earth, but a few individual crystals have survived, needles in a planetary haystack. These tiny but tough crystals are called zircons, not unlike cubic zirconia in wedding rings. The best place to find Hadean zircons is in the Outback of Western Australia, a lonely place called the Jack Hills. It is here that we find the oldest stuff on Earth, zircons 4.4 billion years old or January 14th on the Calendar.

Episodes 10 through 16 covered these Jack Hills zircons. Every element within the minerals has been interrogated for Earth’s earliest stories. Through these crystal balls, we can see the broad picture of the Hadean world, but the details are hazy- Just like early astronomers looking at other planets. We know Earth’s first crust was made of dark volcanic basalt with pale granite pockets. How much granite? That’s up for debate. The first oceans formed as the Earth was pelted by asteroids bringing ice from outer space. Where were the asteroids from? That’s up for debate. Scientists have also found traces of carbon inside the Jack Hills zircons, the building blocks of life. But does that mean there was life back then? That’s also up for debate. Despite all these frustrating caveats, it’s impressive we know anything about the Hadean at all.

Which brings us to today. It’s finally time to say goodbye to the Jack Hills zircon crystals, our constant companions for seven episodes. I don’t know about you, but I’ll miss these little guys.

That’s because from here, the story only gets hazier. Western Australia is not the only place with Hadean zircons, but it is certainly the most fruitful. All other locations combined only have a few dozen crystals to work with. These places include: China, India, Brazil, Canada, Greenland, and South Africa. If you just can’t get enough Hadean zircons, check out my interview with Dr. Nadja Drabon, where we talk about her new discoveries from South Africa.

So, if we’ve run out of crystals, where do we go from here? Do we just jump forward into Season 2? Not yet, but we’re getting close. There are a few Hadean stories that are beyond the scope of zircons, but still deserve to be told. In Episode 16, we asked a simple question: “Is there any trace of life inside the Jack Hills zircons?” The answer is: we’re not sure yet. We see carbon that might have been inside living things… or maybe not.

As we move away from the Jack Hills, we start to tackle one of the most important topics of this entire podcast- the origins of life. But before we can ask the big questions like “What is life?” or “When did life first evolve?”, we need to start with the fundamentals, questions that can be more easily digested. Today’s question is: “What is life on Earth made of?”.

In this episode, we’ll meet three essential ingredients in every living thing, then we’ll start searching for these tiny pieces in future episodes. This quest for the oldest life will take us from the deepest reaches of space, to black castles boiling under the sea, to laboratories where slime forms from thin air. But it starts much closer to home, inside your own body.

Part 2: What Are You Made Of?

Different levels of organization in organisms.

Before we begin, take a moment to appreciate your body and mind. No matter what condition you’re in, no matter what you’re doing right now, you are a fascinating group of moving pieces working together, from the atomic level to the brain processing every word I’m saying right now. Give yourselves a pat on the back for making It this far, whatever you’ve made it through. 

With that in mind, let come back to today’s question: “What is life on Earth made of?” Or, to put it another way, “What are you, the listener, made of?”

There are many ways to answer this question- it all depends on what scale you’re looking at. Let’s start big and work our way down the ladder of size. Your biggest building blocks are organs- your brain, your heart, your stomach. But if we look around the universe, we don’t see random organs floating around in space, thank goodness. In fact, most living things don’t have organs like we do. Jellyfish don’t have brains or hearts, and single-celled life like bacteria are literally too small.

In this podcast, we won’t see living things with organs until the very last season. The same is true for the building blocks of organs: tissues like muscle or skin. To make the earliest life, we need to look at simpler pieces.

If a single cell like a bacterium or yeast doesn’t have organs or tissues, what does it have? The answer is right in the name- a single cell, an organic bubble filled with DNA and a few other materials, depending on how fancy the critter is. Every living thing on Earth has at least one cell, and the human body has 100 trillion cells. For reference, the Milky Way Galaxy only has 100 billion stars, so you have a thousand cells for every star you see in the night sky. 

Cells are much simpler than organs or tissues, but they’re still intricate, complex living machines. Cells do not simply pop into existence- they need to be built. To build a cell, you need two basic things: 1: simple building material, just like houses are built from brick and steel. 2: The energy to pull everything together. A pile of bricks and steel cannot make a house by itself without energy put into it, like a team of construction workers.

In fact, your body is doing this right now- as you grow, your cells divide over and over again, but one cell can’t become two without the raw materials or the energy to start building. So how did this all start?

Before we start investigating how life started from scratch in the Hadean, we need to see how it builds itself today. And the best place to look is in the kitchen. As I’ve said before- any good road trip needs snacks.

Part 3: You Are What You Eat

Every time you eat, you’re giving your cells the building blocks and the energy they need to build themselves. These pieces are called molecules, they’re the next step down from cells on the size ladder. Molecules are made by shoving different atoms together, like carbon, oxygen, or hydrogen.

Atoms and molecules are both microscopic, and it’s easy to confuse the two in everyday conversation. In short, atoms are the building blocks of molecules. Think of atoms like tiny balls covered in velcro. If you shove multiple atoms together, they stick together and make a lumpy larger shape- a molecule. One helpful way to remember the difference is the word “atom” is smaller than “molecule”, just like atoms themselves are smaller.

The recipes for some molecules are very simple- one oxygen plus two hydrogen makes H2O, or water. The molecules that build your body are much more complex, with dozens or thousands of atoms making long weird shapes. We don’t have time to cover every single molecule inside your cells, but they can be divided into a few big families.

At this point the podcast will sound more like a nutrition guide because the three families we’ll meet today are proteins, carbs, and fats. Each of these molecules is used as a construction material or an energy source for your cells, and each can be found in the food we eat every day. For an example, let’s make a ham and cheese sandwich for lunch.

Let’s start with the ham. You might know that ham is a good source of protein. But what is protein, and what does it do? To come back to our construction analogy, protein is more of a building block, a brick than an energy source. This idea is easy to remember- bodybuilders usually have high-protein diets to grow muscles. Even if you’re not going to the gym every day, proteins also help build your hair, nails, bones, and the organs we mentioned earlier. Proteins have a lot of other cool jobs, but we’ll get to those in later episodes.

Amino acids building into proteins

Proteins are small compared to cells, but they are still huge molecules, with thousands of atoms tangled together like electrical wires. If we take the time to straighten out a protein, we can finally zoom in and see smaller molecules, lined up in a row like beads on a necklace, or lights on a Christmas tree.

These smaller pieces are called amino acids. Amino acids only have around a dozen atoms, so are they’re much easier molecules to make. Many have strange names like threonine and alanine, but there’s one amino acid you might have heard of- especially around the holidays. Its’ name is tryptophan, and it’s famous for making people sleepy.

In the United States, the word tryptophan often comes up around Thanksgiving time. Families get together, chow down on a huge turkey dinner, then head to their separate corners to sleep off their meals. Most people blame their post-dinner sleepiness on the tryptophan in turkey meat.

This is half-true. In fact, plenty of other foods have more tryptophan, like egg whites, cod, and soy. So eating tofurkey should make you sleepier than regular turkey. The real culprits behind your holiday naps are another family of molecules: carbohydrates, or “carbs” for short. To make a long story short, carbs make it easier for tryptophan to enter the brain and make you sleepy. Just eating turkey alone won’t put you to sleep. If you want to avoid passing out after a holiday meal, skip the bread, not the meat.

Speaking of which, let’s return to our sandwich. If the proteins in ham are the building blocks of cells, the carbs in bread are a major energy source. Remember, a carb molecule has a lot of different atoms stuck together. Breaking these bonds releases some energy. This energy is then put to work elsewhere in your cells. All molecules can be broken down for energy, but carbs are easier to break than proteins. In short, they give you more bang for your buck.

Starch, a complex carbohydrate made of individual sugar molecules

Just like protein molecules are made from smaller amino acids, carbs are made of smaller sugar molecules. Some sugar chains are very short, while others are extremely long. Simple carbs like pure sugar are very easy to break, giving you a big jolt of energy all at once. Anyone who’s given candy to a child knows this fact first-hand. Larger, more complex carbs like starch are harder for cells to digest, stretching out the energy over a longer period of time. Some carbs like fiber and cellulose are too complicated for the body to break, but they’re often used as building blocks in other living things- most notably, wood in plants. Molecules can have more than one job in the natural world- carbs are more than just energy sources.

Which brings us to our final family: fats. In our sandwich, we can find fats in the cheese, the butter or mayo, and a little bit in the ham. Fats often get a bad rap in diets, but they are very important to survival. If proteins are the building blocks of cells, and carbs are the energy, what do fats do? A little bit of both.

Fat molecules forming bubbles in water

Fats are excellent sources of energy for cells to use. On average, a molecule of fat will give you twice as much energy as a carbohydrate. This is why foods with a lot of fat and simple sugar taste so darn good- your body is telling you they’re valuable sources of energy to survive. One big difference between fat and sugar is that fat takes longer to digest. A sugar high comes and goes very quicky, but fat can stick around for long time, which is why it can be harder to get rid of.

But there is a silver lining to having fats in our bodies, or should I say, a cellular lining. As I mentioned before, cells are essentially bubbles that contain DNA and other bits. It’s easy to focus on the DNA and nucleus, but we shouldn’t forget that without the humble outer membrane, without that bubble, there is no cell at all, no life as we know it. That outer bubble is made from fats.

You can see a similar structure when you put a drop of vegetable oil in water. Oil and water do not mix, and you’ll see the oil forming tiny circles or bubbles. Why? Fat molecules like oil have one end that hates water, and one end that loves water. All the water-hating ends cluster together in the center, forcing all the water-loving ends away to form a protective bubble. The fats on the outside of your cells are doing something similar- protecting your DNA from the harsh outside world.

So, what about DNA? How does it relate to fats, proteins and carbs? Come to think of it, how did these three very different materials link together in the first place? Now we’re asking the right questions for future episodes, but for now, I think it’s time to sit back, eat our sandwich, and digest what we’ve just learned.

Summary:

Living things on Earth are made of cells. These cells are made of smaller building blocks, which need energy to pull together. Three main ingredients for cells are found in the food we eat every day. Proteins help form a cell’s structure, carbs give a cell the energy to grow, and fats do a bit of both. These materials are not alive themselves, but together, they help make every living thing on Earth today.

Next episode, we’ll search for these three ingredients across the universe, and learn how they were delivered from space to the Hadean Earth.

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Thank you for listening to Bedrock, a part of Be Giants Media.

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