0:00:07.618,0:00:09.747
If someone called you scum,

0:00:09.747,0:00:11.451
you'd probably be offended,

0:00:11.451,0:00:12.868
but scientifically,

0:00:12.868,0:00:14.451
they might not be far off.

0:00:14.451,0:00:15.503
Have you ever thought about

0:00:15.503,0:00:17.367
where your food comes from?

0:00:17.367,0:00:18.721
You might say it comes from

0:00:18.721,0:00:20.404
plants, animals, or even fungi,

0:00:20.404,0:00:21.960
but you'd probably rather not

0:00:21.960,0:00:23.720
think about the rotting organisms and poop

0:00:23.720,0:00:26.867
that feed those plants, animals, and fungi.

0:00:26.867,0:00:29.352
So really, you and most of the matter in your body

0:00:29.352,0:00:31.935
are just two or three degrees of separation

0:00:31.935,0:00:34.772
from things like pond scum.

0:00:34.772,0:00:36.564
All species in an ecosystem,

0:00:36.564,0:00:38.109
from the creatures in a coral reef

0:00:38.109,0:00:39.485
to the fish in a lake

0:00:39.485,0:00:40.821
to the lions on the savannah,

0:00:40.821,0:00:42.362
are directly or indirectly

0:00:42.362,0:00:44.325
nourished by dead stuff.

0:00:44.325,0:00:46.826
Most of the organic matter in our bodies,

0:00:46.826,0:00:48.617
if we trace it back far enough,

0:00:48.617,0:00:50.413
comes from CO2 and water

0:00:50.413,0:00:52.249
through photosynthesis.

0:00:52.249,0:00:54.070
Plants use the energy from sunlight

0:00:54.070,0:00:57.178
to transform carbon dioxide and water from the environment

0:00:57.178,0:00:59.587
into glucose and oxygen.

0:00:59.587,0:01:01.283
That glucose is then transformed

0:01:01.283,0:01:02.701
into more complex organic molecules

0:01:02.701,0:01:06.845
to form leaves, stems, roots, fruit, and so on.

0:01:06.845,0:01:08.764
The energy stored in these organic molecules

0:01:08.764,0:01:11.557
supports the food chains with which we're familiar.

0:01:11.557,0:01:13.950
You've probably seen illustrations like this

0:01:13.950,0:01:15.537
or this.

0:01:15.537,0:01:16.981
These green food chains

0:01:16.981,0:01:19.241
start with living plants at their base.

0:01:19.241,0:01:22.034
But in real-life terrestrial ecosystems,

0:01:22.034,0:01:23.989
less than 10% of plant matter

0:01:23.989,0:01:26.002
is eaten while it's still alive.

0:01:26.002,0:01:27.701
What about the other 90?

0:01:27.701,0:01:29.159
Well, just look at the ground

0:01:29.159,0:01:30.326
on an autumn day.

0:01:30.326,0:01:32.079
Living plants shed dead body parts:

0:01:32.079,0:01:33.748
fallen leaves, broken branches,

0:01:33.748,0:01:35.501
and even underground roots.

0:01:35.501,0:01:36.919
Many plants are lucky enough

0:01:36.919,0:01:38.617
to go their whole lives without being eaten,

0:01:38.617,0:01:41.254
eventually dying and leaving remains.

0:01:41.254,0:01:44.540
All of these uneaten, undigested, and dead plant parts,

0:01:44.540,0:01:47.200
that 90% of terrestrial plant matter?

0:01:47.200,0:01:48.846
That becomes detritus,

0:01:48.846,0:01:51.700
the base of what we call the brown food chain,

0:01:51.700,0:01:54.034
which looks more like this.

0:01:54.034,0:01:55.475
What happens to plants

0:01:55.475,0:01:58.064
also happens to all other organisms up the food chain:

0:01:58.064,0:01:59.398
some are eaten alive,

0:01:59.398,0:02:00.818
but most are eaten only

0:02:00.818,0:02:02.609
when they're dead and rotting.

0:02:02.609,0:02:04.142
And all along this food chain,

0:02:04.142,0:02:06.031
living things shed organic matter

0:02:06.031,0:02:07.655
and expel digestive waste

0:02:07.655,0:02:10.700
before dying and leaving their remains to decay.

0:02:10.700,0:02:13.246
All that death sounds grim, right?

0:02:13.246,0:02:14.581
But it's not.

0:02:14.581,0:02:16.584
All detritus is ultimately consumed

0:02:16.584,0:02:18.533
by microbes and other scavengers,

0:02:18.533,0:02:21.169
so it actually forms the base of the brown food chain

0:02:21.169,0:02:23.452
that supports many other organisms,

0:02:23.452,0:02:25.368
including us.

0:02:25.368,0:02:26.701
Scientists are learning

0:02:26.701,0:02:27.469
that this detritus

0:02:27.469,0:02:29.712
is an unexpectedly huge energy source,

0:02:29.712,0:02:31.885
fueling most natural ecosystems.

0:02:31.885,0:02:34.182
But the interactions within an ecosystem

0:02:34.182,0:02:36.476
are even more complex than that.

0:02:36.476,0:02:38.118
What a food chain really represents

0:02:38.118,0:02:40.651
is a single pathway of energy flow.

0:02:40.651,0:02:42.694
And within any ecosystem,

0:02:42.694,0:02:43.859
many of these flows

0:02:43.859,0:02:44.987
are linked together

0:02:44.987,0:02:46.363
to form a rich network of interactions,

0:02:46.363,0:02:48.739
or food web,

0:02:48.739,0:02:52.243
with dead matter supporting that network at every step.

0:02:52.243,0:02:53.538
The resulting food web

0:02:53.538,0:02:54.617
is so connected

0:02:54.617,0:02:55.829
that almost every species

0:02:55.829,0:02:58.032
is no more than two degrees from detritus,

0:02:58.032,0:03:00.002
even us humans.

0:03:00.002,0:03:01.616
You probably don't eat rotting things,

0:03:01.616,0:03:03.783
poop, or pond scum directly,

0:03:03.783,0:03:06.091
but your food sources probably do.

0:03:06.091,0:03:07.841
Many animals we eat

0:03:07.841,0:03:09.927
either feed directly on detritus themselves,

0:03:09.927,0:03:11.851
like pork, poultry, mushrooms, shellfish,

0:03:11.851,0:03:15.475
or catfish and other bottom feeders,

0:03:15.475,0:03:16.891
or they are fed animal by-products.

0:03:16.891,0:03:19.686
So, if you're thinking nature is full of waste,

0:03:19.686,0:03:20.945
you're right.

0:03:20.945,0:03:23.566
But one organism's garbage is another's gold,

0:03:23.566,0:03:25.025
and all that rotting dead stuff

0:03:25.025,0:03:27.152
ultimately provides the energy that nourishes us

0:03:27.152,0:03:29.070
and most of life on Earth,

0:03:29.070,0:03:30.992
as it passes through the food web.

0:03:30.992,0:03:35.175
Now that's some food for thought.