Ch-2: The Origin and Evolution of the Earth
Early Theories (Puraani Soch)
Nebular Hypothesis: Ise Immanuel Kant ne diya tha aur Laplace ne 1796 mein revise kiya.
- Iske mutabiq, planets ek dhire ghumte hue "cloud of material" (Nebula) se bane jo suraj se juda tha.
- Baad mein Otto Schmidt aur Carl Weizascar ne kaha ki suraj ke charo taraf Hydrogen, Helium aur dust ka ek disk-shaped cloud tha.
- Planets Accretion (particles ka judna) ke process se bane.
Modern Theory: The Big Bang
Big Bang Theory: Ise "Expanding Universe Hypothesis" bhi kehte hain. 1920 mein Edwin Hubble ne iska saboot diya.
- Tiny Ball: Shuruat mein saara matter ek "Tiny Ball" (Singularity) ke roop mein tha jiska volume chota par temperature aur density infinite thi.
- Explosion: 13.7 billion years pehle ek bada dhamaka hua jisse universe expand hone laga.
- Temperature Drop: Pehle 3 minutes mein pehla atom bana. 3 lakh saal baad temperature 4,500 K tak gir gaya aur universe transparent ho gaya.
- Example: Ek balloon par dots lagakar use fulao (inflate karo), dots ek dusre se dur jayenge. Ye universe ke expansion jaisa hai.
Star and Planet Formation
- Stars: Nebula mein gas ke "lumps" bane jo apni gravity se dense bodies ban gaye. Ye 5-6 billion years pehle hua.
- Planets: Nebula ke andar gas ka core bana aur charo taraf rotating disc bani. Matter condensed hokar Planetesimals bana aur collision se planets bane.
- Light Year: Yeh distance ka unit hai (not time!). Light 3,00,000 km/sec ki speed se chalti hai.
Evolution of the Earth (Dharti ka Vikas)
Shuruat mein Earth rocky, barren (banjar) aur hot thi, jisme Hydrogen aur Helium ka patla atmosphere tha.
Differentiation Process: Garmi ki wajah se matter apni density ke hisab se alag hone laga.
- Bhari matter (jaise Iron) centre mein chala gaya (Core bana) aur halka matter satah (surface) par aa gaya (Crust bana).
- Earth ki layers: Crust, Mantle, Outer Core, Inner Core.
Atmosphere aur Hydrosphere
Atmosphere 3 stages mein bana:
- Loss of Primordial Atmos: Solar winds ne pehle wali Hydrogen/Helium gas ko uda diya.
- Degassing: Earth ke andar se gases (Water vapour, Nitrogen, CO2) bahar nikli.
- Photosynthesis: Life ne oxygen release karna shuru kiya.
Example: Barish ka pani depressions mein jama hua aur Oceans bane (lagbhag 4,000 million years pehle).
Origin of Life
- Life lagbhag 3,800 million years pehle shuru hui.
- Ye ek chemical reaction thi jisne inanimate matter ko living substance mein badal diya.
- Puraane blue algae ke fossils 3,000 million years purane hain.
--- EXERCISE SOLUTIONS ---
1. MCQs: (i) c - 4.6 billion years, (ii) b - Differentiation (atmos se related nahi hai), (iii) d - 3.8 billion years.
2. Short Answers (30 Words):
- (i) Differentiation: Density ke hisab se matter ka layers mein batna (jaise Iron ka core mein jana).
- (ii) Initial Earth: Rocky, hot aur barren, jahan sirf Hydrogen aur Helium thi.
--- PROJECT WORK: STARDUST ---
Project "Stardust" NASA ka mission tha jo comets se dust samples collect karne ke liye banaya gaya tha taaki universe ki history pata chal sake.