[soft music] (host) Thank you to Brilliant.org for supporting PBS Digital Studios.

Come in, come in.

Greetings, home planet, and all hail our supreme Zork-Dorg.

Mission update.

I've completed my biological analysis of this planet's life forms, and there is a lot of something called cows as well as ants.

I'm glad we don't have ants on our home planet.

There are a lot of them.

Wow!

I've concluded that this planet is actually run by small birds called chickens.

They outnumber humans two to one.

Not very smart, but I think they're planning something.

These humans think they're in charge!

[laughs] Now they actually do kill a lot of stuff.

More research is needed.

I'm going to go eat something called chicken nuggets with spicy barbecue sauce, fries, and a milkshake, for research!

Wish me luck.

More research to come.

[bright music] What would it look like if we or aliens posing as YouTubers took a census of all Earth's life and put it on a scale to see what dominates and if we're changing it?

Well, there are a lot of humans on Earth, about 7.6 billion, in fact.

But there are actually way more chickens--19 billion-- and way, way more fish.

Those estimates are in the trillions.

We humans actually make up 1/100th of 1% of all life on Earth by mass.

That hasn't stopped us from having a big-time impact, though.

Sure, we've altered the landscape, which is actually visible from space, and we've literally moved mountains.

But there's also an impact that's a bit harder to see.

All the death!

Since our species spread across the globe, we've trampled out 84% of animals and over half of all plant life.

Sheesh!

So what's left?

Counting individual animals is hard and boring, and it would take a really long time.

So instead, scientists often measure something called biomass , basically how much living mass there is in some group of species.

We measure biomass in gigatons of carbon.

This is helpful when you want to compare species of different sizes.

For example, 3,100 mice have the same biomass as one human, or 15,312 humpback whales have the same biomass as your mom.

[horn whimpers] Real mature, guys!

Scientists recently found our planet hosts a total of 550 gigatons of living carbon.

So how does all that stack up?

Let's start with animals.

Of all animals, mammals and birds only make up 8.5%, and among that, 60% is livestock, mostly cattle and pigs.

Humans--we're more than a third of all birds and mammals, but we're only 3% of the animal tally.

Arthropods, the insects, spiders, crustaceans, and other things with exoskeletons far outweigh any other animal group making up 60% of the animal kingdom.

I mean, the termites alone nearly outweigh all 7.6 billion of us humans.

But altogether animals are a tiny point, 3% of Earth's living mass.

Mushrooms and other fungi are six times more massive than all the animals.

There's actually a colony of mycelium, an underground fungus, fungi, fungusi in Oregon that stretches 1,665 football fields in area.

It's considered the largest organism on Earth.

However, even fungi and fungals are just a tiny fraction of biomass compared to another group, one that's absolutely massive despite being mini.

A typical bacterial cell is a 10th the size of your typical animal cell, yet together bacteria are a whopping 35 times more massive than all animals put together.

Bacteria, they make up most of the small world, but the other groups of microscopic critters each individually outweigh birds and mammals on the biomass scale.

I guess it's a small world after all.

But bacteria aren't the biomass masters.

The true rulers of Earth's biosphere are plants.

Our green friends make up a whopping 83% of all biomass.

This results surprise scientists because we tend to think of bacteria playing the biggest role in Earth's biosphere.

But when you think about how heavy a tree is and the fact that there's 3 trillion trees on Earth, their top spot makes sense.

But then you think about the fact they did all of that by eating air!

Although most of Earth's surface is covered by ocean, turns out most of life, 86%, lives on land.

It might be a blue planet, but it's a green biosphere.

And even more surprising, there's almost 12 times more life deep below the ground, mostly microbes than there is in the ocean.

So that's how life on Earth measures up.

Thing is, that tally used to look pretty different in the past.

Humans and our close relatives have only been around about 6 million years, but in that short time we've managed to decimate life on this planet.

From 50,000 to 3,000 years ago, half of Earth's large mammal species died out due in part to human activity.

Whaling alone decreased marine animal biomass fivefold just since the 1700s and things like deforestation, hunting, and destroying habitats have knocked down terrestrial animals by a factor of six since we showed up.

Don't even get me started on climate change!

Actually do get me started and go check out our new climate environment channel called "Hot Mess," link in the description.

Where were we?

Yeah, humans have also added new life to the mix.

The planet now hosts more livestock than wild birds and mammals, and to feed ourselves and all those animals, we've permanently cultivated nearly 600,000 square miles.

If you add in pastures and stuff, about 18.9 million square miles have been totally turned over to agriculture, and our livestock are hogging 68% of that.

Human population growth is slowing, but it's still going up.

By 2050, we'll have something like 9.7 billion people aboard spaceship Earth.

And who knows what that additional human biomass will do to the planet.

If we keep adding more cows and chickens and people, lions and tigers and bears might only exist in story books.

Plants, bacteria, and chickens, though, will probably still be here.

Stay curious.

Hey, I just wanna say a big thank you to this guy and this beard.

Go check out Wheezy Waiter.

A big thank-you to Brilliant.org for supporting PBS Digital Studios.

This episode was inspired by a recent research paper I read: "The Biomass Distribution on Earth."

Those researchers relied on hundreds of studies about individual groups of plants and animals and microbes to arrive at these estimates of Earth's total biomass.

It was a really impressive feat, and it involved a lot of careful mathematical analysis.

If you want to sharpen your skills for viewing the world around you more mathematically, check out Brilliant.org.

They have a course all about probability, which will show you how everything from sports to stock markets to science can be understood better by using probability.

Brilliant's lessons come in bite-sized pieces, and the problems feel a lot more like games, which beats just memorizing stuff.

Brilliant--it's math and science done right, proud to support "It's Okay to be Smart."

To learn more about Brilliant, go to brilliant.org/besmart.

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