Hi! I'm Emily from MinuteEarth. Or, as I've
sometimes heard it pronounced, "my-nute Earth."
Coming up, we've got four short stories about the science of size,
why big things are big, small things are small,
and as far as Mother Nature is concerned, size really does matter.
First up, a quest for the biggest organism on the planet.
Blue whales are the biggest animals ever to exist on Earth.
They can weigh upwards of 150 tons, which is more
than the largest dinosaurs. But the blue whale is not the biggest living thing.
That title goes to... well, it depends on what you mean by "biggest." The tallest may be
a California redwood nicknamed "Hyperion." At a towering 115 meters,
this giant is taller than the Statue of Liberty. The most extensive organism is
a very old humongous fungus that covers a whopping
2385 acres in a national forest in Oregon. At the base of trees, bunches of
honey mushrooms appear. They are the fruiting bodies produced by the fungus,
which otherwise lives out of sight. Imagine if apple trees grew underground
and only the apples apples were visible to us. That's basically what the fungus does,
except that it spreads its mycelia not just through the soil, but also through the
roots and bark of trees in the forest, attacking them and stealing their
nutrients, so it can continue spreading outwards. However, if we're talking about the
good old heaviest organism ever found, that prize goes to a giant panda
living high on a Utah plateau.
Just kidding. It goes to a single quaking aspen named "Pando"
that weighs over 6000 tonnes, as much as 40 blue whales. If you go to the
Fish Lake National Forest, though, you won't see a giant tree trunk. You'll just
see a forest of regular sized trees. But thanks to genetic testing,
we've  learned that this stand of aspen
covering 106 acres of land is actually a
single clonal organism that grew from a
lone seed long ago. That single tree was
able to spread so much because its roots
send up shoots that grow into what look
like individual trees. Since all 47,000
trees are part of the same organism, the
forest behaves somewhat unusually. For
example, the entire forest transitions
simultaneously from winter to spring and
uses its vast
network of roots to distribute water and
nutrients from trees with plenty to
trees in need. Speaking of water, if you
include water when weighing these giant
organisms, then the humongous fungus
might actually way more than Pando but
foresters at least care only about the
mass actually produced during growth, the dry mass.
And since fungi are mostly
water,
Pando wins. Either way it's likely that
some of the below ground connections
whether roots or mycelia, have become
severed over time, meaning these giants
are probably comprised of smaller but
still ginormous and genetically
identical patches. And finally, because of
the extensive testing required to
confirm "biggest anything" claims, the
fungus and Aspen can only profess to be
the largest living organisms ever found. There may be even bigger monsters
lurking right under our feet just
waiting to be discovered.
So, it's possible that the biggest
organism hasn't been discovered yet,
even if it isn't possible that that organism is an underground panda.
The thing is, though, animals don't just
wake up one day gigantic. Something weird
has to happen to make them that way.
Animals come in all different sizes but
usually over evolutionary time each type of animal stays roughly the same size.
Every once in a while though, something
crazy happens that allows an animal to
get truly gigantic. Take insects and
other arthropods, which have tiny bodies,
in part because they breathe by sponging up air through their exoskeletons,
and the available oxygen can only diffuse so far before getting used up. If they had
bigger bodies oxygen wouldn't reach far
enough inside. But about 300 million years ago,
Earth's atmospheric oxygen
levels spiked. With more oxygen in the
air, arthropods' bodies could grow way bigger,
leading to mega-bugs like a dragonfly
the size of an eagle, and a millipede the
size of a two-person kayak. Dinosaurs on
the other hand got pretty darn big
without any outside help, but at some
point they hit a limit due to the
so-called "square-cube law": body strength is based on a cross sectional area of bones and muscles,
but weight is based on
volume, and just like doubling the height
of a cube causes its cross-sectional area to
get four times larger but its volume to
get eight times larger, when an animal
gets bigger, it does get stronger, but it
gets WAY heavier. Fossil evidence
suggests that dinos were nearing the
size of which they could no longer lug
around their own bodies, when they
stumbled upon an evolutionary
breakthrough: a system of air pockets and air sacs throughout their skeletons that
allow them to get bigger without getting
heavier, and have incredibly long but light
necks, which granted them access to a
huge bounty of leaves. Eventually though,
a group of land animals got around the
square-cube problem altogether by
climbing back into the water, which
buoyed their weight. And since they took
their lungs with them into the water,
they could breathe oxygen-rich air,
rather than being stuck with oxygen-poor
water, allowing these mammals to grow
almost twice as big as the biggest fish.
But these giant creatures just didn't
have enough food to get any gianter than
that. Then, a few million years ago,
changing ocean currents brought tons of
nutrients up from the depths, which fuel
huge localized phytoplankton blooms,
which in turn attracted enormous
concentrations of scrumptious zooplankton. With this new "krillion"-calorie diet
together with their air-breathing lungs
and water-supported bodies,
blue whales quickly tripled in size
to become not just gigantic, but truly
the largest animals to have ever lived.
And that is certainly something to spout about.
In the ocean life comes in all sizes.
It turns out that we humans need to be
eating more of the small stuff.
Anyone who goes fishing probably has a story about the one that got away.
"It was this big, don't cha know!" Yeah, that was a bummer, but it's actually quite important
that big fish get away, both for fish and
fishermen. For most of the species that
we fish, commercial and recreational
fishermen are only allowed to keep
individuals above a minimum legal size. The idea behind these laws is to protect
juveniles so they can grow big enough to
reproduce at least once before becoming
our dinner. In theory, that means there
will always be enough fish for dinner
tomorrow, and ensuring dinner for
tomorrow is important enough that the
English Parliament discussed protecting
young―that is, small―fish as early as 1376,
and today it's a common regulation for fisheries worldwide,
except it doesn't really work. 
First, large individuals have the
greatest number of successful offspring,
both because bigger fish produce more
eggs and because the eggs they produce
also contain a more generous food supply
for the baby fishies. So by removing the
largest individuals of a given species,
we severely decrease the population's
ability to replenish itself. Second, if we
only remove the largest fish, that means
fish that are small for their age and
thus smaller when they first reproduce, 
are more likely to live long enough to
make babies, so individuals with small
fish genes tend to stay in the water,
reproduce and pass on their genes to new
generations, while big fish and big fish genes
become rarer and rarer. We're
basically breeding smaller fish,
unintentionally, and it's not a small
change. Size-selective fishing has caused
the body mass of large commercial fish
to be cut in half over the last 40 years.
Let me say that again. Heavily-fished
fish are now half the weight they used
to be. Six-year-old haddock, for example,
weigh 40% of what they did in 1970
Imagine if full-grown men weighed 65
pounds! Clearly, size-selective fishing
means fewer and smaller fish in the
water, which suggests it's not the best
way to keep our fish supply stocked for
future human generations.
And in fact, there's a new idea called
"balanced harvesting" ready to save the
day. Instead of reeling in all the
largest individuals, fishermen would
catch a smaller number of fish across a
wider range of sizes, keeping the numbers
and sizes of fish... well, balanced. However, old habits die hard, and the use of size
limits is deeply ingrained in our
collective fisheries management DNA, but
sooner rather than later, we'll have to accept that it's good to
let some of the big ones get away, for
only they can change the course of fish-tory.
Fish-tory! We can't be proud of all of
our puns, but while we're talking tiny and
water, let's talk about tiny water. How
many water molecules does it take to make a drop?
Somewhere inside of every
raindrop is a tiny impurity―a touch of
salt, a speck of soot, a grain of clay―that's absolutely crucial to the
raindrop's existence. In fact, without
these microscopic pieces of dirt there
would be no rain because water vapor
can't condense into droplets on its own,
which is kind of weird because water
molecules like each other. If they didn't,
they wouldn't cling to each other like
this, and in the air vaporized water
molecules collide and stick together all
the time, but they also break apart all
the time, thanks to bond-breaking heat energy.
Only when the air cools down past a certain point called the "dew point" does this
breaking apart slow down enough for
little clusters of water molecules to
grow into droplets. But actually, that's
only true if the cluster is big to start with.
If it's too small its surface is so
curved that the molecules on the outside
have few neighbors to bond to which
makes them easy to break off so the
cluster as a whole has higher chances of
losing molecules than gaining them, even
below dew point, which means that up
until a certain critical size, a cluster's
chances of shrinking are better than its
odds of growing. Unfortunately, that
critical size is 150 million molecules,
and while there are
millions of 5-molecule clusters in a golf ball-sized volume of air at dew point, odds are that
only one of those clusters will grow to
a size of 10, and you'd need a golf ball
of air 10 million miles across to find a
single 50 molecule cluster, which
basically means that clusters of water
molecules
never get to that 150 million mark on
their own. Fortunately, they don't have to!
They can start off at that critical size
by condensing onto one of the gajillions
of little pieces of dirt floating in our
atmosphere and then grow and grow until
they're a droplet in a rain cloud and
ultimately it's these little pieces of
dirt surrounded by water that make life
possible on our big piece of dirt
surrounded by water.
And, from my spot on
this big piece of dirt, thanks for watching!
