Biochemical Origin of Life - First step: Origin of Earth and its Primitive Atmosphere

Age and Origin of Earth:

• Earth formed about 5–6 billion years ago.
• It originated as part of the process that formed the solar system, from hot cosmic material and gases.

Early Nature of Earth:

• Initially, Earth was a fiery, spinning, hot mass of gases and vapours.
• Surface was barren, rocky and very hot, with no stable landforms or water bodies.
• There was no life and no atmosphere like the present one.

Cooling and Condensation:

• Over millions of years, Earth gradually cooled.
• Hot gases and vapours condensed and different substances separated based on density (relative heaviness).

Heavy Metals → Core

• Heavy metals (iron, nickel, copper, etc.) moved inward.
• They formed the dense central core of the Earth.

Medium-Weight Elements → Outer Shell / Lithosphere

• Medium-weight elements (sodium, potassium, silicon, aluminium, magnesium, sulphur) remained above the core.
• They formed the outer rocky shell, which became the lithosphere.

Light Gases → Primitive Atmosphere

• Light gases (hydrogen, helium, nitrogen, oxygen, carbon compounds, argon, water vapour, etc.) rose outward.
• These gases collected around Earth and formed the primitive atmosphere

• Formed from lightest gases escaping outward from the hot interior.
• Composition (just before origin of life) mainly included H₂, CH₄, NH₃ and water vapour.
• No free molecular oxygen (O₂) in the beginning; the atmosphere was reducing, not oxidising.
• Created conditions that later favoured chemical evolution and the origin of life.

A-C. Condensation of hot gases and vapours of various elements to form primitive Earth

• The Earth is believed to have originated about 5–6 billion years ago from cosmic dust or as a part separated from the Sun during the formation of the solar system.
• Early Earth was a hot, molten, and gaseous mass with no atmosphere, gradually cooling over millions of years.
• During cooling, heavy elements formed the core, medium-weight elements formed the mantle and crust, while light gases accumulated to form the primitive atmosphere.