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Oceans
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Second segment of the Ocean Odyssey describes how the oceans formed and the role of salt in creating currents.
We're getting close! Isn't it 21DD? There it is!
00:00:00
DD for Dr. D? He has his own boat dock?
00:00:09
Come over here! Welcome to the MAURI, Tidewater Community College's research vessel!
00:00:16
Dr. D, we learned about waves and tides, but we need to know more about oceans.
00:00:30
Let's start at the very beginning. You know how oceans formed?
00:00:40
You mean they weren't always here?
00:00:43
No, not always. When the Earth began about 4.6 billion years ago,
00:00:45
volcanic eruptions helped to form an atmosphere. That included water vapor.
00:00:49
So were the oceans created when it rained?
00:00:53
That's right. About 3.8 billion years ago, the lower areas of the Earth's crust called basins filled with rainwater.
00:00:55
If the ocean is made from rainwater, why is it salty?
00:01:01
Well, in the beginning it wasn't very salty.
00:01:04
So how did it get that way?
00:01:06
One way is from freshwater rivers. As they flow towards the oceans,
00:01:08
rivers dissolve minerals such as salt from the land, adding salt to the ocean.
00:01:11
But how can the ocean be more salty than the rivers?
00:01:15
When water evaporates from the oceans, it takes almost pure water away, leaving the salt behind.
00:01:17
Then for millions of years, the rivers carried salt into the oceans, and evaporation leaves it there.
00:01:22
Do the oceans continue to get saltier?
00:01:27
No, and they're not getting any less salty either.
00:01:29
We say saltiness, or salinity, has reached equilibrium.
00:01:32
Why is the salinity of seawater so important?
00:01:35
One reason is that it's a major factor in creating ocean currents.
00:01:38
Let's do an experiment.
00:01:41
We're going to pour salty water into fresh water. Let's see what happens.
00:01:43
The salty water went to the bottom. Why is that?
00:01:48
Salty water sinks to the bottom because it's denser than fresh water.
00:01:52
A gallon of salt water weighs more than a gallon of fresh water.
00:01:55
Jacob, test it out.
00:01:58
They both feel the same.
00:02:02
Salt water from the ocean is only about 3% heavier than fresh water.
00:02:04
But even a small difference in density makes a real difference in currents.
00:02:07
Is there anything other than salinity that determines the density of water?
00:02:11
Yes, the temperature does.
00:02:15
I think we're going to have to learn more about how density makes currents.
00:02:17
I have a friend named Dr. Martens who can help you.
00:02:20
He's doing research in an underwater laboratory called Aquarius.
00:02:22
I'll give you his contact information.
00:02:25
Thanks, Dr. D.
00:02:27
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- Idioma/s:
- Niveles educativos:
- ▼ Mostrar / ocultar niveles
- Nivel Intermedio
- Autor/es:
- NASA LaRC Office of Education
- Subido por:
- EducaMadrid
- Licencia:
- Reconocimiento - No comercial - Sin obra derivada
- Visualizaciones:
- 623
- Fecha:
- 28 de mayo de 2007 - 15:34
- Visibilidad:
- Público
- Enlace Relacionado:
- NASAs center for distance learning
- Duración:
- 02′ 31″
- Relación de aspecto:
- 4:3 Hasta 2009 fue el estándar utilizado en la televisión PAL; muchas pantallas de ordenador y televisores usan este estándar, erróneamente llamado cuadrado, cuando en la realidad es rectangular o wide.
- Resolución:
- 480x360 píxeles
- Tamaño:
- 15.14 MBytes