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How Does Life Work?

Biosphere Process

Rock Cycle:
The Marriage of Water and Rock


Everything in the Biosphere is part of one system, so Rock Cycles could be discussed under Circles as well as under Biosphere. The Water Cycle and the Rock Cycle are closely interlinked, as if they were partners in a long marriage. Everything really is connected to everything else.

The creation and movement of rock around the earth is the rock cycle. It is a very slow process that happens over millions and millions of years. 

People have been finding fossils of ocean creatures high up in the mountains for hundreds of years. How they got there was once a great mystery of science.  Now we know that some of the land on each continent was once the ocean floor. This former ocean floor was slowly, slowly uplifted as continental tectonic plates collided.

This mountain was under water once. It still is, 
but now it's under snow and ice.

a fossil trilobite in limestone

The Rock Cycle is coupled with the Water Cycle. Every time water touches rock, it tries to dissolve it, and it does dissolve a tiny bit. The dissolved mineral from the rock becomes part of the water and travels with the water through the ground or down the rivers.

Living organisms partner with water to dissolve rock. Lichens, and mosses to some extent, secrete acids that weather rock surfaces and begin the long process of turning rock into soil.

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. Soil bacteria help water to dissolve rock particles in soils.

Every river on earth contains dissolved rock. Rivers also contain rock particles in suspension. These minerals are washed into the ocean, where they become part of the bodies of a multitude of living organisms. Without the dissolved rock brought by rivers to the ocean, most ocean life would die.

Weathering: What Else Wears On Rock?

The Rock Cycle is so slow that human eyes cannot see it. Glaciers are one slow power working on the rock of mountains. The glaciers are rivers of ice that do flow, but only a few feet a year. They grind over bedrock and break it up into boulders, then pebbles. What we ordinarily call gravel was left behind by melting glaciers. Rivers running out from beneath glaciers are sometimes "milky" with mineral content .

Glacier at its starting point,
carving rock and carrying rock

Glacier at its end, 'calving'
icebergs into the ocean


The Winds work on rock too. Wind has a lot to do with turning rocks into sand, which is simply very small pebbles called grains. Wind can grind rock right down to dust. Sometimes when wind is wearing rock, it creates beautiful sculptures, such as these:

Hoodoo at Arches Nat. Park

Pinnacles at Arches Nat. Park

Temperature Changes work on and wear down the hardest rocks. When rock gets cold it shrinks a little. When rock gets warm, it expands a little. When this seesaw expansion and contraction goes on for a few hundred years, or a few thousand, or million, the rock gets tired and breaks.

Water gets into the action here, too. Rock often has small cracks in it. Water seeps into the cracks, and when it freezes, it expands, which eventually can break the rock apart.

Another power working on rock is life. Living systems such as lichens slowly dissolve rock by using chemicals they create.

Wind action, temperature change, and rainfall, all working together is called Weathering.

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 rock. Rivers carry this dissolved rock into the world-ocean. (They also carry rock particles, or sediment, but that's a different process.)

Question: So, why isn't the ocean filled up with rock? 

Easy Answer: Because the rock is dissolved.

Try a Mind-Experiment: Imagine dissolving table salt or sugar into a glass of water. Say you tried to dissolve a half-cup of salt or sugar in one glass of water. Stir like crazy. From your own experience, you know that a lot of the salt would just fall to the bottom of the glass and refuse to dissolve. You have just reminded yourself that water can hold only a limited amount of dissolved salt or sugar. Water can only hold a certain amount of dissolved minerals.

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 thousand million-year-periods. 

Two questions:

1. So what really does happen to all that dissolved rock? 

2. Why haven't the continents just dissolved and disappeared?

 Answer 1. The Marriage of Life and Rock. Living organisms take the minerals out of solution and make room for more dissolved rock. The particles of rock that are carried in suspension are pulled to the seafloor by gravity. Tiny floating plankton organisms called diatoms (a kind of algae) and foraminifera, dinoflagellates, and radiolarians (kinds of protozoa) make beautiful microscopic shells, called tests,out of the dissolved calcium and silica and carbon they take out of ocean water.

diatom test

foramiferan test

diatom test

radiolarian test

a foramiferan test

a dinoflagellate test

They live in their shells, and when they die, they drift down to the ocean floor in a slow steady rain of tiny shells. Billions of tons of these shells accumulate on the ocean floor every year. These sediments 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 eventually ends up as rock on the ocean floor.

A little of the dissolved rock does just 'fall out' (precipitate) of the water onto the ocean floor, but most of it is processed by life. This life process is called carbon burial. If life did not take so much carbon out of the cycle for eons, carbon dioxide might increase in the air and overwarm Earth--the greenhouse effect. Explore further: Balance

Plankton drifters such as diatoms aren't the only life forms taking minerals out of the water. Bacteria take a lot of minerals out, too. Bacteria can concentrate different minerals inside their tiny bodies. Some bacteria specialize in dissolved metals, such as iron. Very long ago certain early bacteria concentrated iron in their bodies and died and accumulated on the ocean floor and eventually created most of the iron ore deposits that we mine today. Bacteria that concentrated aluminum in their cells created the bauxite (aluminum ore) deposits that we mine today.

Question 2. Why haven't the continents just dissolved and disappeared?

The short answer is that the continents are always being renewed. Rock circulates from the ocean depths back onto land.

Earth is covered with plates of floating crust rock. They 'float' on magma, which is semi-liquid rock beneath the crust. Some of the rock created on the ocean floor ever-so-slowly sinks down under the plates at their edges and melts into the magma. This is called subduction. Here is a diagram of a deepwater ocean plate (oceanic lithosphere) sinking into the mantle where it collides with the continent of South America (continental lithosphere.

You already know one way the melted seafloor rock can get back onto the continents. Right. Volcanoes. Lava is magma raised to the surface of the continents.

Typical volcano cone
Volcano erupting underwater. The steam and smoke show the violent collision of lava and seawater. Many islands have been born this way.

Continents are renewed through a process called Uplift. Remember now that these crustal rock processes are extremely slow--to us. When tectonic plates collide, sometimes one sinks below the other. Other times they 'rub' against each other and cause earthquakes. But fairly often in the history of Earth, both colliding plates push upward. Example: When the Indian sub-continent (modern India plus) broke free from Gondwanaland (see above) long ago, it floated north until it collided with the Asian plate. That collision pushed the edges of both plates upward and created the Himalaya Mountains. Remember that the rock cycle begins again on "new" mountains. Glaciers and rivers and wind begin to carve them away and carry their particles and dissolved minerals back to the ocean, where they were before--perhaps several times before. It is very hard to imagine the enormous stretches of Deep Time that the Rock Cycle takes to complete a cycle.

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Explore Further in Biosphere

Biosphere: Introduction
Biosphere as Place: Introduction
Biosphere as Ocean: Life Zones
Biosphere as Ocean Floor: Benthic Biomes One
Biosphere as Ocean Floor: Benthic Biomes Two
Biosphere on Land: Terrestrial Biomes
Biosphere on Land: Anthropogenic Biomes
Biosphere as Process: Introduction
Biosphere Process: Floating Continents, Tectonic Plates
Biosphere Process: Photosynthesis
Biosphere Process: Life Helps Make Earth's Crust
Biosphere Process:
Rock Cycle--Marriage of Water and Rock
Biosphere Process: Marriage of Wind and Water
Biosphere Process: Gas Exchange
Biosphere as An Expression of Spirit
The Ecological Function of Art
The Earth Goddess
The Tree of Life
The Green Man
Earth Art
Biosphere as Community
Biosphere Microcosm: Bacteria and Archaea
The Procaryote Domain
Biosphere Microcosm: Germs
Biosphere Community: The Eucaryote Domain
Biosphere Community: Protists 1: Algae
  Biosphere Community: Protists 2: Protozoa
Biosphere Community: Plants: What's New?
Biosphere Community: Plant Diversity--Major Groups
Biosphere Community: Plant Defense
Biosphere Community: Plant Pollination
Biosphere Community: Plant Seed Dispersal
Biosphere Community: Kingdom Animals
Biosphere Community: Kingdom Fungi
Biosphere Community: Six Great Extinctions
Return to Ecology Index