Origin of the atmosphere

EPS 212 - Lecture 05 Origin of the atmosphere

• The original atmosphere

– Probably made up of hydrogen and helium.

– These are fairly common in the universe.

• Original atmosphere stripped away by the solar wind

– H and He are very light

• Hydrogen and helium have the smallest atoms by mass.

– The early earth was not protected by a magnetic field.

– Thus the current atmosphere is secondary

The secondary atmosphere

• Formed from degassing of volcanoes

• Gasses emitted probably

similar to the gasses emitted by volcanoes today.

– H₂O (water), 50-60%

– CO₂ (carbon dioxide), 24%

– SO₂ (sulfur dioxide), 13%

– CO (carbon monoxide), – S₂ (sulfur),

– Cl₂ (chlorine), – N₂ (nitrogen), – H₂ (hydrogen),

– NH₃ (ammonia) and – CH₄ (methane)

Modern atmosphere

Nitrogen (N2)- 78%,

Oxygen (O2)- 21%,

Carbon Dioxide (CO2) 0.03 %,

Where did all the

oxygen come from?

Volcanic Volcanic

outgassing outgassing

Modern Modern

Atmosphere Atmosphere H H

₂₂

O O – – 50 50 - - 60% 60% N N

₂₂

– – 78% 78%

CO CO

_{2 2}

– – 24% 24% O O

₂₂

– – 21% 21%

SO SO

₂₂

– – 13% 13% CO CO

₂₂

– – 0.03% 0.03%

1. Where did all the O₂ come from?

2. Where did all the CO₂ go?

Formation of the oceans

• The earth is cool enough that H₂O condenses to form the oceans.

– Estimates of the amount of H₂O outgassed is not enough to fill the oceans

– It seems likely that a large

volume of water was added by the impact of icy meteors on the atmosphere.

• CO₂ dissolves into the oceans.

In the oceans life evolves

• Ingredients necessary for life

– NH₃ – ammonia – CH₄ – Methane – H₂O – Water

• These can produce amino acids, the

building blocks of life

• • Life may have originated Life may have originated

–– under the primitive under the primitive

atmosphere atmosphere

–– or at hydrothermal vents or at hydrothermal vents

deep in the oceans deep in the oceans

–– or deep in the earth

or deep in the earth’’s s crust

crust

Life changes the atmosphere Life changes the atmosphere

• • With the evolution of life the first cellular With the evolution of life the first cellular organisms (cyanobacteria) began to use organisms (cyanobacteria) began to use the gasses in the early atmosphere (NH the gasses in the early atmosphere (NH

₃₃

– – ammonia, CH ammonia, CH

₄₄

– – methane, H methane, H

₂₂

O O – – water) for energy.

water) for energy.

• • Where did the O Where did the O

₂₂

come from? come from?

– – Produced by photosynthetic life. Produced by photosynthetic life.

• • Where did the CO Where did the CO

₂₂

go? go?

– – Dissolves in water in the oceans Dissolves in water in the oceans

– – Used by life by photosynthesis and buried Used by life by photosynthesis and buried when plants and micro

when plants and micro - - organisms die. organisms die.

•• The source of coal and oilThe source of coal and oil

Early history of life and the Early history of life and the

atmosphere atmosphere

• • The Earth is about 4.5 billion years old. The Earth is about 4.5 billion years old.

• • Life first appears in the oceans at least 3.5 billion Life first appears in the oceans at least 3.5 billion years ago.

years ago.

• • 0.9 billion years ago there is enough oxygen in 0.9 billion years ago there is enough oxygen in the atmosphere to produce the ozone layer and the atmosphere to produce the ozone layer and

life can finally move onto land.

life can finally move onto land.

–– The ozone layer protects the earth from harmful ultra The ozone layer protects the earth from harmful ultra violet radiation from the sun.

violet radiation from the sun.

The other planets The other planets

Venus Venus

–– Closer to the sunCloser to the sun

–– Very hot at the surface so Very hot at the surface so water vapor in the

water vapor in the

atmosphere does not atmosphere does not

condense.

condense.

•• Runaway greenhouse effect Runaway greenhouse effect (482(482^ooC, 900C, 900^ooF).F).

–– No oceans or rainfall so No oceans or rainfall so COCO₂₂ does not dissolve.does not dissolve.

–– Has a very dense Has a very dense atmosphere.

atmosphere.

From Venera 13

The other planets The other planets

Mars Mars

–– Further from the sunFurther from the sun –– Smaller than EarthSmaller than Earth

–– So small that most of the So small that most of the atmosphere escaped into atmosphere escaped into

space.

space.

–– No oceans or rainfall so No oceans or rainfall so COCO₂₂ stays in atmosphere.stays in atmosphere.

–– 98% of atmosphere is 98% of atmosphere is COCO₂₂..

• • Jupiter Jupiter

–– Huge (318x earthHuge (318x earth’s ’s mass)

mass)

–– Kept all its original Kept all its original atmosphere

atmosphere

–– 80% Hydrogen80% Hydrogen –– 20% Helium20% Helium

Summary Summary

1 1

^stst

atmosphere atmosphere

H and He from H and He from

solar nebula solar nebula

Lost to solar wind Lost to solar wind

2 2

^ndnd

atmosphere atmosphere

H H

₂₂

0, CO 0, CO

₂₂

and SO and SO

₂₂

from volcanic

from volcanic degassing

degassing

Transformed by Transformed by

photosynthesis photosynthesis Current

Current

atmosphere atmosphere

N2, O2, from N2, O2, from

photosynthesis photosynthesis

and constant N2 and constant N2

production

production