BIOGEOCHEMICAL CYCLES

Everything goes around and around and around ……………………….

Law of Conservation

• Matter cannot be create or destroyed• It simply changes forms• Bottom line is there is a fixed amount of stuff• We’re not making any more atoms (elements)• They move around the systems• Where they are located in the system effects the

system

An Amazing Thought

• While the things made up of the atoms may be young, you for example, the atoms that you are made of have been around since the beginning of the universe.

• Your atoms could have been part of an ancient tree, or a dinosaur!

• Kind of weird isn’t it?

Plate Tectonics and the Rock Cycle

• The rock cycle is the result of earth moving matter (rocks and minerals) via plate movement (plate tectonics)

• The atoms that make up rocks and minerals start out in the mantle and eventually end up back in the mantle

• Lets take a look.

Rocks

• Two or more elements combine to make minerals• Two or more minerals combine to make a rock• There are three types of rocks• Igneous rocks form from cooled magma• Sedimentary rocks are pieces of minerals or organic

material cemented together• Metamorphic rocks are formed when either igneous

or sedimentary rocks are subjected to enormous heat and pressure

Igneous rocks

• Magma is molten rock inside the earth

• Think of it like a molten elemental soup

• Does magma have a lot of energy or a little energy?

• What does that tell you about the motion of the atoms in the magma?

Cooling

• As energy leaves the magma, the atoms slow down enough to begin to bond

• They arrange themselves into regular patterns

• The rate of cooling determines the size of the crystal patterns in the rock

• Would you expect magma inside the earth or out on the surface to cool faster?

Plutonic or Intrusive Rock

• Magma inside the earth loses energy slower than magma on the surface

• The elements have more time to form mineral crystals

• Subsequently, the mineral crystals are bigger in intrusive igneous rock formed by cooling magma below the surface

Volcanic or Extrusive Rock

• Magma that comes to the surface is called lava

• It cools considerably faster

• Subsequently, extrusive rock lacks the distinct mineral crystals / grains found in plutonic rock

• It is still made of the same elements

Weathering

• As soon as rock is exposed to earth’s surface, it is exposed to processes that break it back down into individual mineral crystals (we typically refer to them as sand)

• This process is called weathering

• There are two types of weathering, mechanical and chemical

Mechanical Weathering

• Mechanical weathering or disintegration occurs when the rock is broken into progressively smaller pieces without changing it’s chemical composition

• This is PHYSICAL change• I have the same basic mineral crystals I’m

just breaking them into smaller pieces• Example:• Beating a rock into sand with a hammer

Causes of Mechanical Weathering

• Wetting and drying

• Freezing and thawing (Ice wedging)

• Plant roots

• Contact with other rocks– Rock slides or avalanches– Washing down rivers

Chemical Weathering

• In chemical weathering the agent essentially changes the mineral crystal into something else

• This is CHEMICAL change

• The resulting substance no longer looks like or has the same properties it did before

Chemical Change Agents

• Hydrolysis– Water combining with the minerals

• Oxidation– Oxygen combining with the minerals

• Carbonic Acid– Carbon dioxide combining with water then

dissolving the minerals

Erosion

• All these big and little pieces of weathered rock (sediments) can be moved by the wind and water

• This is the process of erosion, the movement of sediments from one place to another

Deposition

• Eventually the speed of the wind or water carrying sediments slows and it cannot support the weight of the sediments

• The sediments fall and begin to stack up in layers

• This is called deposition• As the wind or water slows, which size

sediments will fall out first and which last?

Rocks GravelSand

ClaySilt

Current

FastSlow

Sedimentary Rock

• As the sediments and the remains of living organisms get buried deeper, they can become cemented together to form sedimentary rock

• Clastic: Formed from cemented pieces of other rocks

• Organic: Formed from the remains of plants and animals

Metamorphic Rocks

• Rocks that are formed from other rocks when they are exposed to enormous heat and pressure

• Igneous or sedimentary rock that has been exposed to enormous heat and pressure (for example at plate boundaries) literally gets squished becoming denser and changing appearance

The Rock Cycle

• The movement of elements through this system is called The Rock Cycle

Elemental Soup

• Magma cools allowing the elements to slow down and start to bond

• 1or more elements combine to make minerals, 2 or more minerals combine to make rock

• The slower magma cools the bigger the crystals

Weathering

• As soon as the rock is exposed at the surface, it comes under attack

• Wind, water and chemicals are the enemy

• These agents break the rock down physically or chemically

Erosion

• The rock particles are carried off by the wind and water to be deposited

Sedimentary Rock

• The sediments pile up over time

• As the sediments are buried they can become cemented together becoming sedimentary rock

Metamorphic Rocks

• Anywhere Igneous or Sedimentary rocks are exposed to enormous heat or pressure they can be turned into metamorphic rocks

Sedimentary rock

Metamorphic Rock

Igneous Rock

And Back to Element Soup

Some Things to Remember

• The process takes thousands or millions of years

• There is no set pattern to the process. Metamorphic rocks can be uplifted and weathered etc.

• The bottom line is the elements that start in the magma eventually end up back there.