How a single-celled organism almost wiped out life on Earth - Anusuya Willis
-
0:08 - 0:10There's an organism
that changed the world. -
0:10 - 0:14It caused both the first mass extinction
in Earth's history -
0:14 - 0:17and also paved the way for complex life.
-
0:17 - 0:18How?
-
0:18 - 0:22By sending the first free oxygen
molecules into our atmosphere, -
0:22 - 0:25and they did all this
as single-celled life forms. -
0:25 - 0:27They're cyanobacteria,
-
0:27 - 0:29and the story of these simple organisms
-
0:29 - 0:32that don't even have nuclei
or any other organelles -
0:32 - 0:35is a pivotal chapter
in the story of life on Earth. -
0:35 - 0:39Earth's atmosphere wasn't always
the oxygen-rich mixture we breathe today. -
0:39 - 0:433.5 billion years ago, the atmosphere
was mostly nitrogen, -
0:43 - 0:44carbon dioxide,
-
0:44 - 0:46and methane.
-
0:46 - 0:49Almost all oxygen was locked up
in molecules like water, -
0:49 - 0:51not floating around in the air.
-
0:51 - 0:53The oceans were populated by
anaerobic microbes. -
0:53 - 0:58Those are simple, unicellular life forms
that thrive without oxygen -
0:58 - 1:01and get energy by scavenging
what molecules they find. -
1:01 - 1:04But somewhere between
2.5 and 3.5 billion years ago, -
1:04 - 1:07one of these microbial species,
-
1:07 - 1:09probably floating
on the surface of the ocean, -
1:09 - 1:12evolved a new ability: photosynthesis.
-
1:12 - 1:16Structures in their cell membrane
could harness the energy from sunlight -
1:16 - 1:20to turn carbon dioxide and water
into oxygen gas and sugars, -
1:20 - 1:22which they could use for energy.
-
1:22 - 1:27Those organisms were the ancestors
of what we now call cyanobacteria. -
1:27 - 1:29Their bluish color comes from
the blue-green pigments -
1:29 - 1:32that capture the sunlight they need.
-
1:32 - 1:36Photosynthesis gave those ancient bacteria
a huge advantage over other species. -
1:36 - 1:38They could now produce their own energy
-
1:38 - 1:41from an almost endless supply
of raw ingredients, -
1:41 - 1:43so their populations exploded
-
1:43 - 1:48and they started polluting the atmosphere
with a new waste product: oxygen. -
1:48 - 1:52At first, the trickle of extra oxygen was
soaked up by chemical reactions with iron -
1:52 - 1:54or decomposing cells,
-
1:54 - 1:56but after a few hundred million years,
-
1:56 - 2:00the cyanobacteria were producing oxygen
faster than it could be absorbed, -
2:00 - 2:02and the gas started building up
in the atmosphere. -
2:02 - 2:05That was a big problem for the rest
of Earth's inhabitants. -
2:05 - 2:08Oxygen-rich air
was actually toxic to them. -
2:08 - 2:09The result?
-
2:09 - 2:14About 2.5 billion years ago was a mass
extinction of virtually all life on Earth, -
2:14 - 2:16which barely spared the cyanobacteria.
-
2:16 - 2:19Geologists call this
the Great Oxygenation Event, -
2:19 - 2:22or even the Oxygen Catastrophe.
-
2:22 - 2:23That wasn't the only problem.
-
2:23 - 2:27Methane had been acting as a potent
greenhouse gas that kept the Earth warm, -
2:27 - 2:33but now, the extra oxygen reacted with
methane to form carbon dioxide and water, -
2:33 - 2:35which don't trap as much heat.
-
2:35 - 2:36The thinner atmospheric blanket
-
2:36 - 2:40caused Earth's first,
and possibly longest, ice age, -
2:40 - 2:42the Huronian Glaciation.
-
2:42 - 2:44The planet was basically
one giant snowball -
2:44 - 2:46for several hundred million years.
-
2:46 - 2:48Eventually, life adjusted.
-
2:48 - 2:51Aerobic organisms,
which can use oxygen for energy, -
2:51 - 2:55started sopping up some of the excess
gas in the atmosphere. -
2:55 - 2:57The oxygen concentration rose and fell
-
2:57 - 3:01until eventually it reached
the approximate 21% we have today. -
3:01 - 3:04And being able to use
the chemical energy in oxygen -
3:04 - 3:07gave organisms the boost they needed
to diversify -
3:07 - 3:09and evolve more complex forms.
-
3:09 - 3:12Cyanobacteria had a part
to play in that story, too. -
3:12 - 3:14Hundreds of millions of years ago,
-
3:14 - 3:19some other prehistoric microbe
swallowed a cyanobacterium whole -
3:19 - 3:22in a process called endosymbiosis.
-
3:22 - 3:26In doing so, that microbe acquired
its own internal photosynthesis factory. -
3:26 - 3:29This was the ancestor of plant cells.
-
3:29 - 3:32And cyanobacteria became chloroplasts,
-
3:32 - 3:35the organelles that carry out
photosynthesis today. -
3:35 - 3:39Cyanobacteria are still around
in almost every environment on Earth: -
3:39 - 3:40oceans,
-
3:40 - 3:41fresh water,
-
3:41 - 3:42soil,
-
3:42 - 3:43antarctic rocks,
-
3:43 - 3:44sloth fur.
-
3:44 - 3:46They still pump oxygen
into the atmosphere, -
3:46 - 3:51and they also pull nitrogen out to
fertilize the plants they helped create. -
3:51 - 3:53We wouldn't recognize life on Earth
without them. -
3:53 - 3:54But also thanks to them,
-
3:54 - 3:57we almost didn't have
life on Earth at all.
- Title:
- How a single-celled organism almost wiped out life on Earth - Anusuya Willis
- Description:
-
View full lesson: http://ed.ted.com/lessons/how-a-single-celled-organism-almost-wiped-out-life-on-earth-anusuya-willis
There’s an organism that changed the world. It caused the first mass extinction in Earth’s history … and also paved the way for complex life. How? Anusuya Willis explains how cyanobacteria, simple organisms that don’t even have nuclei or any other organelles, wrote a pivotal chapter in the story of life on Earth.
Lesson by Anusuya Willis, animation by Augenblick Studios.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 04:14
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Marta Konieczna
An error in English transcription: 2:41: 'blanket' instead of 'planet'