Cycles of the Earth

Cycles of the Earth

• EARTH RECYCLES ALL MATTER FORMING ITS OUSIDE LAYERS – Analyze cycles based on the “reservoirs” that hold matter and

the movement of matter between reservoirs

• 3 MAJOR CYCLES– Hydrologic

• Recycling of water molecules

– Atmospheric• Recycling of air molecules

– Rock cycle• Recycling of Earth’s solid materials

Cycles of the Earth

• HYDROLOGIC CYCLE– Water evaporates from oceans– Rises and cools– Falls back to earth as rain– Forms lakes, rivers, ice caps, glaciers, and groundwater

reservoirs• Current Distribution (approximate)

– 96% in oceans (marine - salt)– 3% in ice caps and glaciers (fresh)– 1% in groundwater (fresh)– 0.009% in lakes, rivers, and streams (fresh)

• Fresh Water Supply– 98% of world’s fresh water is groundwater– Stored in underground reservoirs (”aquifers”)

Cycles of the Earth

• ICE AGES– Last several million years– Glaciers repeatedly advance and retreat during the ice age– Interglacial periods occur several times between major advances of glaciers, and last for

approx.40,000 years– Cyclic glaciation periods occurred relatively often in past 2 million years

• GLOBAL CLIMATE CHANGES– Occur in cycles– Explained by Milankovitch (early 20th century)– Due to Earth’s

• Precession• Change in axis of rotation• Elliptical orbit

• OCEANS– Contain vast majority of Earth’s water supply– Undergo chemical cycles– Salt is primarily from sodium and chloride ions, although contains other dissolved minerals

as well– Average time an atom stays in ocean water before removed by some chemical reaction is

“residence time”

Cycles of the Earth

• INTERESTING WATER FACTS– In 100 years a water molecule spends

• 98 years in the ocean• 20 months as ice• 2 weeks in lakes and rivers• Approx. 1 week in the atmosphere

– All water eventually flows to the oceans.• In North America, for example

– Rain falling to west of Continental Divide flows to the Pacific.– Rain falling to east of Continental Divide flow to the Atlantic.

– The average ocean depth is 10,000 feet.– The longest river is the Nile.– The river carrying most water is the Amazon.– The Great Lakes contain 95% of the fresh surface water in the

U.S. and 20% of the world’s fresh water.

Cycles of the Earth

• ATMOSPHERIC CYCLE

– COMPOSITION (AT THE PESENT TIME) OF EARTH’S ATMOSPHERE• 78% nitrogen• 21% oxygen• Less than 1% argon• 0.01% - 5% water vapor• 0.035% carbon dioxide

– WEATHER – changes frequently• Temperature

– Varies with altitude• Pressure

– Decreases significantly with altitude• Humidity

– Measures atmosphere’s variable water content• Cloudiness

– Closely related to humidity• Winds

– A consequence of atmospheric convection

– CLIMATE – shows little change on a human scale• Average weather conditions of an area over a period of several years• Changes slowly in response to ocean circulation, the Sun’s output, the position of the continents and mountain ranges, and

other relatively fixed conditions.

Cycles of the Earth

• ATMOSPHERIC CYCLE– LAYERS OF AIR

• 1st layer above Earth’s surface (Troposphere)– Approximately 10 miles high– Contains approx.75% of all atmospheric molecules – Only layer where “weather” occurs

• 2nd layer above Earth’s surface (Stratosphere)– From approximately 10 to 30 miles high– Contains majority of remaining air molecules– Too few molecules present to experience weather– Becomes increasingly colder– Has ozone (O3) layer in lower region

• Beyond the stratosphere– Ranges from very few molecules of air to no molecules of air as you go

higher and higher above the Earth’s surface

Cycles of the Earth

• ROCK CYCLE - cycle of internal and external Earth processes by which rock is created, altered, or destroyed.

• 3 TYPES OF ROCK– Igneous

• Formed by cooling down of hot, molten material• Cooled above or below Earth’s surface

– Extrusive» Cooled above surface» Example – basalt

– Intrusive» Cooled below surface» Example – granite

– Sedimentary• Formed by layers of sediment• Found in locations such as valleys, the base of mountains, ocean basins• Examples – shale, sandstone, limestone

– Metamorphic• Transformed from other rock by tremendous pressures or high temperatures• Examples – slate, marble, schists, gneisses

Cycles of the Earth

• GEOLOGY

– Study of the Earth’s dynamic history

• Analysis of rocks and the features and processes of the Earth’s interior and surface

• “Father of Modern Geology”– James Hutton - 1700’s

– Studied sedimentary rock in Scottish cliff

– Recognized geological forces resulted in changes in the layers

• Longest of the Earth’s 3 cycles