- 4.6 billion years ago
- Sun was formed when gravity pulled material towards the centre (swelling
- Accretion, small grains buildup to form fist sized planets (planet tesema)
- Asteroids and comets occasionally collide into the Earth
The Earth’s Four Spheres:
• Geosphere: solid earth: core( 6000 C ;fluid but solid), mantle (2900km contributes to
the largest component of the Earth), crust
- Outer layer compressing the core
- Mantle: Inner (soft, plastic, and weak) & Outer (cooler, solid) 80% of the Earth
- Asthenosphere: area between the outer mantle and the crust… reason why we
have tectonic plate activity
- Lithosphere (mantle and crust collectively): thinnest layer
• Hydrosphere: water sources, riverine, lacustrines (collective lakes), palustrine
(collective wetland, marshes), ocean…
- Other sources of water come from frozen ice (i.e. Greenland, Arctic & Antarctic
circles 1.8% fresh water)
- Rivers, lakes (fresh water) account for <1%
- Aquifer: regions of subterarian water supply- underground layer of water
(sandwiched btw 2 impermeable layers OR an overlying permeable layer and
underlying permeable material)
- Confined Aquifer and Unconfined aquifer
o Confined: clay or rock (impermeable)
o Unconfined: permeable, also referred to as water-table
• Atmosphere: gaseous layer: N (largest) O (21%) CO2, Ar, He etc..
- Heterosphere: outermost sphere (composition: begins in the exosphere extends
to ~80km) hetro= not UNIFORM!
- Lightest elements found here! (He)
- Homoshpere (extended from 80km to the Earth’s surface)
- ozone found here O3
- Thermoshpere: (heat zone w/in the earth) NOT HOT (less volume of air)
vibrational energy causes HIGH temperatures (e- excited!!)
- Mesosphere (50-80km): coldest b/c particles serve as condensation nuclear
- Stratophere temperature inversion (warms up)~ ↑ absorption of greenhouse gases
- Troposhere: Tropopause: (transition zome btw stratosphere and troposphere)↓
temperature with altitude (-6.4 for ever 1000m rise); higher you go, cooler it
• Biosphere: realms of living organisms, nutrient cycles
- Made of complex organisms: vertebrate, invertebrate, microorganisms, plant
- Nutrient recycling within the biosphere interaction, interdependence,
interconnection among different systems very dynamic and self- sustaining (reciprocal relationship: give&take)
• Carbon Cycle and Nitrogen Cycle
- Photosynthesis (plants absorb CO2 from the atmosphere thus, loose Carbon).
- When trees die, decomposes and Carbon is released (thru pressure & extreme
heating) into the Earth.
- We can gain carbon into the atmosphere from the combustion of coal, forest fires
- The lakes and ocean also absorbs a lot of carbon over the years.
Nitrogen Fixation Cycle
- The process which gaseous form of nitrogen is absorbed by bacteria that dwell
in the roots of trees.
- Convert the gaseous form of nitrogen into ammonia and nitrite ions.
- It becomes part of the tissue of plants.
- Produce NO2 and NH4
Nitrogen Denitrification Cycle:
- Process by which nitrite is converted back into nitrogen gas.
- Must occur for fixation to occur
- Provide N2
Earth as a System
- A system: is an assemblage or a combination of interacting component
- Suprasystem & subsystem: both components needed for the survival of the
- Causes a chain of reaction and changes to other spheres ( interconnected)
emission of greenhouse gases can cause acid deposition & this causes changes in
the pH of water in turn, death to fishes
- Humans interact with the environment
o Size of system
o System interact in complex ways
o Energy and material cycle are essential for the study o