Why is the seabed dark if the water is transparent?
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To understand this, you need to understand the way that light behaves in water. Water molecules ABSORB light when light is in contact with water. That means, in shallow water there’s a lot of light, and you can see everything. As you look deeper and deeper, you will see what happens as more and more water molecules absorb the light. At some point, there is just no light left, and it is pitch black.
Transparency is a spectrum of conditions, ranging from not at all transparent, through somewhat transparent, all the way to quite transparent indeed.
Water isn’t 100% transparent. Some of that light get bounced around through the water and scatters. Not every photon makes it. So the more water there is between you and the observed object, the murkier and darker the object appears.
The same goes for air, only it’s thinner. When you look at objects that are very far away they may appear blue or grey, with desaturated colours and weakened brightness.
Water is transparent to a point…..seawater is more than just water. Salt and other minerals stop light eventually depending on the specific area of ocean
Because water plainly *isn’t* transparent. If it was, you’d be able to see straight down to the bottom of the ocean, and the ocean floor would be brightly lit as you say.
But the fact is that water does block a small amount of light (mostly red light, which is why the ocean is blue). This small amount of opacity isn’t readily apparent when you have, say, a glass of water, but 4000 meters of it is enough to completely block out the sun.
Water is not transparent. It is fairly transparent but not completely, like glass. One pane of glass you can see through it just fine but if you stack a bunch of them they eventually become opaque, just like water. With enough of it the seemingly small amount of light that is absorbed adds up.
To add to what the others are saying- if you’ve ever actually been out on the open ocean and looked into the water, you can see that it’s almost clear. It’s hard to describe without seeing it in person, but you can see the depth to it. It’s not like looking at a blue surface, it’s more like looking at a something blue that’s somewhere beneath the water.
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