Welcome to planet ocean.
0:39For of course, planet Earth is poorly named
0:42and planet ocean is a much more appropriate label.
0:46Why is that?
0:47Well, for a start, 70% of the earth's surface
0:51is covered by ocean.
0:53Let's put that into context.
0:54What that means is that we could put all of the land
0:58into the Pacific Ocean and still have room left over
1:02for nearly two more Australias.
1:05As we'll see later in this module, life
1:08itself evolved in the ocean.
1:10This happened about 3.9 billion years ago
1:13when there was no free oxygen in the atmosphere
1:16and the early cells obtained their carbon--
1:19which is an element essential to all life-- from carbon dioxide
1:24and their energy from inorganic material.
1:28Cyanobacteria are relatively simple single celled organisms
1:33that obtain their energy from photosynthesis.
1:37They evolved in the ocean about three billion years ago,
1:41that's 3,000 million years ago.
1:44And that led to the great oxidation event,
1:472.3 to 2.4 billion years ago, when free oxygen started
1:52to accumulate in the atmosphere.
1:56Multicellular life forms evolved in an oxygenated world
2:00still in the ocean about 600 million years ago,
2:04which eventually led to the colonization of land
2:07about 450 million years ago.
2:11So there's been life in the oceans
2:12about 3.45 billion years longer than there's been life on land.
2:18And there are many reasons why the oceans are
2:21important as drivers of the Earth's system today.
2:24Photosynthesis in the ocean produces
2:26half of the oxygen in the earth's atmosphere.
2:29Parts of the ocean are rich in biodiversity,
2:33easily compatible to tropical rainforests.
2:35And many oceanic regions are at least
2:38as productive as the most intensely managed
2:40agricultural systems.
2:42When it comes to high biodiversity,
2:44it isn't just about coral reefs.
2:47The movie that you're watching now was shot in deep water
2:50off Antarctica.
2:52When it comes to animals, 31 of the 32 major groups
2:56occur in the sea.
2:57And 14 of them are exclusively marine,
3:00with at least five others comprising
3:02mostly marine species.
3:05The oceans also determine, to a very large degree,
3:08the patterns of global and regional climate.
3:11They're the driving force of our weather and climate.
3:15For example, you might know that the El Nino Southern
3:18Oscillation, or ENSO, which is a coupled atmospheric
3:23oceanographic phenomenon that extends across the Pacific,
3:26is highly related to rainfall in central and eastern
3:30Australia and also the Americas, with massive droughts
3:35in Australia under El Nino conditions.
3:38But what you may not realize is the link between the Indian
3:42Ocean Dipole and rain in the top end of Australia,
3:48as well as in southeast Australia.
3:51Like El Nino, the Indian Ocean Dipole
3:54is also a tropical coupled atmosphere ocean phenomenon.
3:58If you're a dairy farmer in Gippsland in Victoria,
4:02the Indian Ocean Dipole might be an important part of your life.
4:06The oceans have a huge role in mitigating
4:08the impact of human driven increases in carbon dioxide
4:12by absorbing much of the carbon dioxide
4:14and the heat that is trapped by the greenhouse phenomenon.
4:18Atmospheric CO2 would be much higher
4:21and the atmosphere would be much warmer if not for the oceans.
4:24But as we shall also see, the oceans
4:26too are subject to very large impacts
4:29driven by climate change.
4:31On the subject of impacts, in modules three and four
4:34we'll talk in more detail about the impacts of climate change
4:38on the ocean system.
4:40And we'll talk about the impacts of a range of other stresses
4:43as well.
4:44And we'll emphasize the kinds of science
4:47that need to be done to ensure responsible stewardship
4:50and management of the oceans in the Earth's system.
4:54Before we move on to the rest of this module
4:57and discuss some of the fascinating habitats,
5:01and ecosystems, and marine diversity that they support,
5:05please go to the discussion forum
5:07and introduce yourself to other participants.
5:10You can use this forum to ask questions and share
5:13ideas during the course.