00:00:10 Every year, plants,
00:00:13 bacteria, and algae earth wide
00:00:18 make around 150 billion metric tons (165 billion tons) of food
00:00:21 for themselves
00:00:23 and almost every other living thing on earth.
00:00:27 How do they do it?
00:00:31 Photosynthesis.
00:00:36 In plants,
00:00:38 this astonishingly intricate process
00:00:40 takes place in a highly organized structure
00:00:42 called a chloroplast,
00:00:45 where a green pigment, chlorophyll,
00:00:48 and other pigments collect
00:00:50 and use the energy from visible light
00:00:52 with amazing efficiency.
00:00:57 In photosynthesis, this energy is used
00:01:00 to do something that happens nowhere else in the natural world
00:01:05 —split water into hydrogen ions and oxygen molecules.
00:01:09 Hydrogen ions combine with carbon dioxide to make sugar,
00:01:13 which can be used by plants to make
00:01:15 all the other complex molecules
00:01:17 that they need to grow.
00:01:22 Most of the oxygen is expelled as an unused by-product,
00:01:27 one that we can’t live without.
00:01:33 About half of the oxygen
00:01:35 we and other organisms breathe
00:01:37 comes from phytoplankton,
00:01:39 microscopic organisms that drift in the ocean.
00:01:44 And the smallest one yet discovered, a cyanobacterium,
00:01:48 is also the most abundant.
00:01:50 Though invisible to the naked eye, these bacteria alone
00:01:55 produce around one fifth of the oxygen on earth.
00:01:58 Nearly all living things need oxygen,
00:02:02 and they depend on other life-forms to make it.
00:02:06 The amazingly complex process of combining carbon dioxide
00:02:10 with the water that constantly cycles on our planet
00:02:14 and energy from the sun
00:02:17 gives us every bite of food
00:02:19 and every breath of air we need.
00:02:22 What do you think?
00:02:24 Did photosynthesis evolve?
00:02:28 Or was it designed?
