Geo101.21.EarthsAtmosphere

Geo101.21.EarthsAtmosphere - Evolution of Earths Atmosphere...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Evolution of Earth’s Atmosphere Atmospheric Formation • The ±rst atmosphere at planet formation (4.57 Ga): – Hydrogen and helium. – Quickly stripped off by the solar wind. Why? • A secondary atmosphere developed via volcanism. Why was this atmosphere not stripped away? – Volcanic gases dominated. • Water (H 2 O). • Carbon dioxide (CO 2 ). • Sulfur dioxide (SO 2 ). • Nitrogen (N 2 ). • Ammonia (NH 3 ). – Free oxygen (O 2 ) was absent. Atmospheric Formation • The secondary atmosphere evolved as the planet cooled. – Water condensed and fell as rain to form the oceans. – Atmospheric CO 2 decreased by dissolving in ocean water. • CO 2 is a powerful heat-trapping (greenhouse) gas. • CO 2 removal permitted atmospheric cooling. – The relative abundance of stable N 2 increased. Atmospheric Formation • By 3.5 Ga, photosynthetic cyanobacteria added free O 2 . • Atmospheric O 2 accumulated. – By 2 Ga, O 2 reached 1% of present value. – Eukaryotic green algae (1.6 Ga) accelerated O 2 production. – By 600 Ma, O 2 arrived at 10% of present concentrations. – Present O 2 concentration (20.9%) by 400 to 250 Ma. Atmospheric Formation • O 2 buildup permitted diversi±cation of life. – Aerobic (oxygenated) respiration is more energy- ef±cient. – Aerobic respiration fueled multicellular life. – High O 2 enabled the possibility of land-dwelling biota. • O 2 Also resulted in the formation of the ozone layer. – Ozone absorbs deadly ultraviolet (UV) radiation. – Prior to the ozone layer, exposed land was bathed in UV. Atmospheric Components • The present atmosphere is comprised of the following gases. – Nitrogen 78% – Oxygen 21% – Other gases 1% • Argon. • Carbon dioxide. • Methane. • Sulfur dioxide. • Ozone.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 8

Geo101.21.EarthsAtmosphere - Evolution of Earths Atmosphere...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online