by John Caddy
I've been thinking about Rivers as the Bringers of Life to all the life that lives in the ocean. In the book of Ecclesiastes in the Christian Old Testament, it says: "All the rivers flow into the sea, yet the sea is not full." This is evidence. It shows that at least three thousand years ago people were actively wondering about rivers and how they work. They were exploring the mysteries of life, even as you are right now.
Today, thousands of years later, we all seem to know at least a little about the water cycle, and other big cycles on earth (like the seasons), and we all know why the sea is not full of water. Evaporation and circulation, right? Sure, but there is something else about cycles that we all don't know. Why isn't the ocean filled up with rock? "Huh? Rock? What kind of dumb question is that?" Water is the most powerful solvent there is. Given enough time, water can dissolve almost anything. Water dissolves iron, water dissolves stone. Water dissolves mountains! Water begins the Rock Cycle.
The Rock Cycle is fundamentally important to ocean life, which is fundamentally important to all life on earth, including you and I. The Rock Cycle is slow, so it's not easy to see. Water plus wind and temperature changes can wear away the hardest rocks. Water as rain and snow and ice (glaciers) travels down watersheds, percolates through soil, dissolves a little sand, comes to the bedrock, dissolves a little rock, carries it all along as an invisible part of the water, and flows into a river. Rivers are full of dissolved minerals, or rock. Rivers carry this dissolved rock into the world-ocean.
So, why isn't the ocean filled up with rock? Easy Answer "Because the rock is dissolved, dummy!" Wrong!!!
Mind-Experiment: Imagine dissolving table salt, or table sugar, into a glass of water. Imagine that you tried to dissolve a half-cup of salt in one glass of water. Stir like crazy. From your own experience, you know that a lot of the salt or sugar would just sit on the bottom of the glass and refuse to dissolve. You have just reminded yourself that water can only hold a limited amount of dissolved salt or sugar. Water can only hold a certain amount of any dissolved minerals or rock.
Ever since land lifted up out of the world ocean and the first continents were born, water has been dissolving the land and rivers have been carrying it back into the ocean. Remember, this has been going on for over three billion years-that is, three million million-year-periods.
Two questions: One: So what does happen to all that dissolved rock? Two: So why haven't the continents just dissolved and disappeared?
Two Real Answers: One: Living organisms take the minerals out of solution and make room for more dissolved rock. Tiny floating plankton organisms called diatoms and foraminifers make tiny beautiful shells out of the calcium and silica and carbon they take out of ocean water. They live in their shells, and when they die, they drift down to the ocean floor in a slow rain of tiny beautiful shells. Billions of tons of these shells accumulate on the ocean floor every year. They get squeezed together by the immense weight of all that water above them, and slowly, slowly, ever-so-slowly turn into rock again. So what began as rock on land ends up as rock on the ocean floor. All this by way of the rivers-the Bringers of Life to the oceans.
One A: Some of the dissolved rock does just 'fall out' (precipitate) of the water onto the ocean floor, but most of it is processed by life.
One B: Plankton critters like diatoms aren't the only ones taking minerals out of the water. Bacteria (the good kind) take a lot of minerals out too. Different kinds of bacteria concentrate different minerals inside their tiny bodies. Some specialize in dissolved metals. Bacteria that concentrated iron very long ago and died and accumulated on the ocean floor created the iron ore deposits that we mine today. Bacteria that concentrated aluminum the same way created the bauxite (aliuminum ore) deposits that we mine today for your Coke and Sprite cans.
Two: This is a partial answer to an enormous question. Plate tectonics is the recently discovered mechanism for how rock circulates from the ocean depths back onto land. We don't understand all of it yet.
Earth is covered with floating 'plates' of crust rock. They 'float' on magma, which is semi-liquid rock beneath the earth's crust. Some of the rock created on the ocean floor ever-so-slowly sinks down under the plates and melts into the magma. You already know how it gets back on the continents. You're right! Volcanoes! Lava is magma raised to the surface of the continents. There are other ways ocean-floor rock becomes land again. Sometimes it is lifted up by a collision of tectonic plates. The important things to realize are that ocean life cannot live without rivers, and the activities of life and rivers are part of earth's way of making rock and recycling rock.
Rivers really are the Bringers of Life to the Sea as long as there is life in the sea, the sea will not be full of rock.
for Global Environmental Education