origin of earth -big-bang hypothesis -origin of

Question

ORIGIN OF EARTH -

BIG-BANG HYPOTHESIS -

• Origin of life is linked to origin of earth.
• Cosmos, the Universe originated 10-20 billion years ago by Big Bang (thermonuclear explosion).
• Its part, a galaxy, (e.g., our Milky Way) comprises millions of stars, (our Sun is one of those).
• Sun, its planets and satellite constitute the solar system.
• Our earth is the 3rd planet with rocks, water & atmosphere.
• It began as gaseous clouds of metals and non-metal atoms, later condensed to form surface rocks and boiling fluid core with gaseous atmosphere.

Chronology of events
Origin	Ago (Billion yrs)
Universe	10-20
Solar system	4.6
Earth	4.5
Oldest surviving rock	4.3
Life (Heterotrophs)	4.2-3.9
Old rock	3.9
Chemosynthetic procaryotes	3.8-3.5
Oldest microfossils (Cyanobacteria)	3.3-3.5
Photosynthetic procaryotes	3.5-3.3
Eukaryotes	1.6-1.5

NEBULAR HYPOTHESIS -

• Earth is formed by gradual condensation of interstellar dust, from which our entire solar system is presumed to be formed.