4. Zemljine sfere / Earth Spheres
A VIEW FROM SPACE...
...helps us to see three major parts of Earth's physical environment: the water (hydrosphere), gaseous envelope (atmosphere), and the solid Earth (geosphere) - see Figure 4.1. It needs to be emphasized that our environment is not dominated by rock, water or air alone; rather it is characterized by continuour interactions as air comes in contact with rock, rock with water, and water with air. Moreover, the biosphere, which is the totality of all plant, animal, and other life on our planet, interacts with all these three physical realms and is an equally integral part of the planet.
Thus, Earth can be thought of as consisting of four major spheres: the hydrosphere, atmosphere, geosphere, and biosphere.
HYDROSPHERE
(figures 4.2 and 4.3)
Earth is sometimes called the blue planet. Water more than anything else makes Earth unique. The hydrosphere is a dynamic mass of water that is continually on the move, evaporating from the oceans to the atmosphere, precipitating back to the land, and running back to the ocean again. The global ocean is the most prominent feature ot the hydrosphere, blanketing nearly 71 percent of Earth's surface to an average depth of about 3800 meters, and acounts for about 97 percent of Earth's water. However, the hydrosphere includes the fresh water found underground and in sterams, lakes, and glaciers.
But this tiny fraction of fresh water is responsible for forming many of our planet's varied landforms and is vital to life on land.
ATMOSPHERE
(figures 4.4 and 4.5)
Earth is surrounded by gaseous envelope called the atmosphere.When compared to the radius of solid Earth (about 6400 kilometers), the atmosphere is a very shallow layer (see figure 4.4). One-half lies belov 5.6 km, and 90 percent occurs within 16 km of Earth's surrface. Still, it is an integral part of the planet that gives us more than air to breathe: protects life from Sun's intense heat and dangerous ultraviolet radiation. The enery exchanges that continually occur between the atmosphere and the surrface and between the atmosphere and space, produce the effects we call weather and climate.
If Earth had no atmosphere it would not only be lifeless but many of the processes and interactions that make the surface such a dynamic place could not operate. Without weathering and erosion, our planet might more closely resemble the lunar surface, which has not changed appreciably in nearly 3 billion years.
BIOSPHERE
The biosphere includes all life on Earth. Ocean life is concentrated in the sunlit surface waters of the sea. Most life on land is also concentrated near the surface. A surprising variety of life forms are also adapted to extreme environments too. Plants and animals depend on the physical environment for the basics of life. However, organisms do not just respond to their physical environment; the biosphere powerfully influences the other thre spheres. Without life, the mekup and the nature of other three spheres would be very different. See the Chapter 8. Evolution through time.
GEOSPHERE
Beneath the atmosphere and the oceans is the solid Earth, or geosphere. It includes all the solid part of the planet, making it by far the larger of Earths speheres. Much of geology stiudies of the solid Earth focuses on the surface features, but by examining the most prominent surface features and their global extent, we can obtain clues to the dynamic processes that have shaped our planet.
Soil, the thin veneer of material at Earth's surface that supports the growth of plants, may be thought of as a part of all four spheres: The solid portion is a mixture of weathered rock debris (geosphere) and organic matter from decaying plant and animal life (biosphere). The decomposed and disintigrated rock debris is the product of the weathering processes that require air (atmosphere) and water (hydrosphere). Air and water also occupy the open spaces between the solid particles and are considered important soil components.
/ Figure 4.1: Photo of the Earth taken by Apollo 17 crew, at December 17th 1972
/ Figure 4.2: The hydrosphere: All Earth's waterin comparisson with Earth
/ Figure 4.3: The hydrosphere: saline and fresh water
/ Figure 4.4: Atmosphere - a very thin envelope!
/ Figure 4.5: Structure of the atmosphere
POGLED IZ VESOLJA...
... nam pokaže tri glavne dele Zemlje: vodo (hidrosfero), plinasti ovoj (atmosfero) in trdni del Zemlje (geosfero) - glej sliko 4.1. Poudariti je potrebno, da našemu svetu ne vladajo kamnine, voda ali zrak posebej. Bolj ga predstavlja neprestana izmenjava na stiku zraka s kamninami, kamnin z vodo in vode z zrakom. Poleg tega biosfera, ki je zbir vsega rastlinskega, živalskega in ostalega življenja na našem planetu, ves čas vpliva na preostale tri sfere in je enakovreden sestavni del planeta.
Lahko torej rečemo, da Zemljo sestavljajo štiri glavne sfere: hidrosfera, atmosfera, geosfera in biosfera.
HIDROSFERA
(sliki 4.2 in 4.3)
Zemljo včasih imenujemo tudi modri planet. Voda, bolj kot karkoli drugega, postavlja Zemljo na posebno mesto med planeti. Hidrosfera je dinamična masa vode, ki se neprestano giblje: izpareva iz oceanov v atmosfero, se v obliki padavin vrača na kopno in odteka nazaj v oceane. Svetovni ocean je največji in najpomembnejši del hidrosfere. Prekriva skoraj 71 odstotkov Zemljine površine, s povprečno globino 3800 metrov in vsebuje okrog 97 odstotkov vse vode na Zemlji. Hidrosfera vsebuje tudi sladko vodo - kot podtalnico, v rekah, jezerih in ledenikih.
Čerpav je delež sladke vode majhen, je oblikoval mnoge od raznolikih pokrajinskih oblik našega planeta, ključen pa je tudi za življenje na kopnem.
ATMOSFERA
(sliki 4.4 in 4.5)
Zemljo obdaja plinasti ovoj imenovan ozračje ali atmosfera. Ta je v primerjavi s polmerom trdne Zemlje (približno 6400 km) zelo tanka plast (glej sliko 4.4)! Polovico jo je v prvih 5,6 km nad površjem in 90% do 16 km nad površjem Zemlje. Vendar je neločljiv sestavni del planeta, ki nam daje več kot le zrak za dihanje: življenje ščiti pred premočno Sončevo toploto in nevarnimi ultravijoličnimi žarki. Energijska izmenjava, ki neprestano poteka med atmosfero in površjem ter atmosfero in vesoljem, povzroča pojave, ki jim pravimo vreme in klima.
Brez atmosfere ne bi bila Zemlja le brez življenja, ampak tudi brez mnogih procesov, ki ustvarjajo tako dinamično površje, kakršnega poznamo danes. Brez preperevanja in erozije bi bil naš planet najbrž precej bolj podoben Luninem površju, ki se v zadnjih treh milijardah let ni opazno spremenilo.
BIOSFERA
Biosfera vključuje vse življenje na Zemlji. V oceanih je življenje najpestrejše v osončenih površinskih vodah. Večina življenja na kopnem je prav tako vezanega na površje. Kljub temu se je mnogo življenjskih oblik prilagodilo tudi ekstremnim razmeram. Rastline in živali so odvisne od okolja v katerem živijo, ob tem pa tudi organizmi močno vplivajo na ostale tri zemeljske sfere. Brez vpliva biosfere, bi bile tudi preostale tri sfere precej drugačne. Poglejte tudi poglavje 8. Razvoj življenja skozi čas.
GEOSFERA
Pod armosfero in oceani je trdna Zemlja ali geosfera. Vključuje ves trdni del planeta in je tako največja od Zemljinih sfer. Velik del geologije trdnega dela Zemlje preučuje površinske strukture, a preučevanje najizrazitejših površinskih struktur in njihova globalna razporeditev, nam pomagata razumeti tudi dinamična dogajanja, ki so oblikovala naš planet.
Prst, ta tanek sloj gradiva na Zemljinem površju, ki omogoča rast rastlin, bi lahko uvrstili kar med vse štiri sfere. Njen trdni del je mešanica preperele kamnine (geosfere) in organskih snovi razpadajočih organizmov (biosfere). Razgrajen in razkrojen drobir kamnin, je rezultat preperevanja, za katerega je potreben zrak (atmosfera) in voda (hidrosfera). Zrak in voda zapolnjujeta tudi prazne prostore med trdnimi delci v prsti in sta njen pomemben sestavni del.