Evolution of the Earth and its Atmosphere and its Atmosphere

Evolution of the Earth and its Atmosphere and its Atmosphere

Evolution of the Earth

and its Atmosphere

4.7 billion years ago:

 The proto-Earth was a loosely-packed ball of “dirt” (primarily

silicon, iron, nickel and their oxides), surrounded by a thin

primordial atmosphere of hydrogen and helium (with traces of

argon, neon and krypton).

4.7 billion years ago – 4.3 billion years ago:

 The planet settled over 400 million years into a densely packed ball,

with a molten core (due to pressure and high levels of radioactivity

 Most of the hydrogen and helium either “escaped” by

absorption of solar radiation or was blown away by the

“solar wind”

 The atmosphere grew even thinner, consisting solely of trace

amounts of hydrogen, helium, argon, neon and krypton

Evolution of the Earth

and its Atmosphere

4.3 billion years ago – 4.0 billion years ago:

 Through fissures in the Earth’s crust, “volcanic outgassing”

spewed vast amounts of hydrogen (H 2 ), nitrogen (N 2 ),

water (H 2 O), carbon monoxide (CO), carbon dioxide (CO 2 ), ammonia (NH 3 ) and methane (CH 4 ) into the atmosphere.

 Most of the H 2 O vapor condensed to form the oceans

 As a result of three key processes (outlined on the next slide),

the air ended up consisting primarily of N 2 , CO 2 and CH 4 , with traces of H 2 , He,

Ar, Ne, Kr, H 2 O, CO and NH 3

 There was still no oxygen gas (O 2 )!

 Moreover, since CO 2 and CH 4 are “greenhouse” gases, the

climate grew much warmer, thereby preventing freezing and accelerating

surface “weathering”

Except for Oxygen, almost all of the Earth’s atmosphere today actually comes from

Process “Equation”

Disassociation of

NH 3 2NH 3 + uv  N 2 + 3H 2

Conversion of some

H 2 O and most CO H 2 O + CO + sunlight  H 2 + CO 2

(As most H 2 O condensed to create the oceans, rain, erosion

and tides began “weathering” the Earth’s surface.)

Carbonate rock formation CaO + CO 2  CaCO 3 (limestone)

(CO 2 absorption) MgO + CO 2  MgCO 3 (dolomite)

Summary: most H Summary: most H 2 escaped; N 2 kept accumulating (since it

at this point).

Evolution of the Earth

and its Atmosphere

4.0 billion years ago – 3.8 billion years ago:

 Volcanic outgassing slowed dramatically while carbonate rock

formation increased, thereby lowering CO 2 levels somewhat

 N 2 and CH 4 continued to accumulate

 The Earth’s surface was still completely unsuitable for supporting

life, due to the atmosphere’s high methane content and excessive

levels of solar ultraviolet radiation

 However, a combination of solar ultraviolet radiation, lightning,

radioactivity and meteorite bombardment of the surface created

complex organic molecules (proteins, amino acids, maybe even DNA).

 Ultimately, this led to the appearance ☻ of primitive one-celled

aquatic organisms which could survive in the oceans.

Life on Earth had begun, despite its inhospitable atmosphere!

Evolution of the Earth

and its Atmosphere

3.8 billion years ago – 2.5 billion years ago:

ability to conduct “photosynthesis”:

(This provided food, in the form of glucose, to these primitive

aquatic plants, and very importantly, began the release of

oxygen into the atmosphere!)

level of about 1% (by volume).

Evolution of the Earth

and its Atmosphere

2.5 billion years ago – 600 million years ago:

photosynthesis continued

into soft-bodied worm-like animals with a variety of organs,

and still later into the first hard-shelled creatures capable of

leaving fossils

about 10% by volume.

ultraviolet radiation and high levels of methane.

Evolution of the Earth

and its Atmosphere

600 million years ago – 3 million years ago:

key processes (outlined on the next slide) completely altered

the atmosphere, enabling plants and animals to leave the

oceans, and survive and evolve on land.

plants and amphibian animals began to appear, and oxygen

levels approached today’s value of nearly 21% by volume

the critically important protective ozone layer was in place.

occasional mass extinction events

Evolution of the Earth

and its Atmosphere

Process “Equation”

(This eliminated most of the atmospheric methane, which

would have been toxic to surface-dwelling animals.)

(This created the “ozone layer” high in the atmosphere, which blocked solar uv from reaching the ground and made it possible for plants and animals to survive above the ocean surface.)

Evolution of the Earth

and its Atmosphere

3.0 million years ago - 200 years ago:

million years ago.

number of “advanced” civilizations developed (and, in some

cases, disappeared).

consumption, as well as metallurgy, became well established

practices.

fuels, was getting underway.

noticeable!

Evolution of the Earth

and its Atmosphere

The Earth and its Atmosphere Today

Planetary Composition

Section Components % by Wt Total %

The Earth and its

Atmosphere Today

100.000

Gases in green are

“greenhouse”

gases!

The Earth and its

Atmosphere Today

Atmospheric Distribution

continues to about 50 km (where

50 km to 80 km (where the

80 km to 160 km with the ionosphere

Danger in the Air

Carbon Dioxide (CO2)

dioxide levels have grown by 25%, from 280 ppm to 350 ppm,

in the last 200 years; moreover this increase is accelerating.

started by lightning), most of it may be traced directly to

human activity, with deforestation for any purpose and fossil fuel burning being the two primary causes

contributing significantly to global warming.

12 years.

Danger in the Air

Methane (CH 4 )

billions years, but in the last 200 years have essentially doubled, from about 800 ppb to roughly 1600 ppb.

agriculture (e.g rice paddies, livestock), sewage treatment, landfill

development and wood burning

global warming.

Danger in the Air

stratospheric ozone layer protects all life on Earth by blocking dangerous solar ultraviolet radiation.

and use of CFCs (as discussed in the next slide).

low altitude ozone is primarily due to the burning of fossil fuels, a human activity.

to global warming, but also a key constituent of urban smog.

Danger in the Air

Chlorofluorocarbons (CFCs)

were, before being banned—used in a variety of industrial

applications: refrigerants, aerosol propellants, frothing compounds, solvents and fire extinguishers

quadrupled from 8 ppb to 3.5 ppb in the last 40 years, largely because they can take decades to break down once released into the air.

global warming.

responsible for the thinning of the ozone layer, through the so-called

“chlorine cycle”:

Danger in the Air

 In the last 200 years, nitrous oxide concentrations in the atmosphere

have increased by 10%, from about 280 ppb to about 310 ppb.

 This growth is a product of both fossil fuel combustion and the

increasingly widespread use of nitrogen-based chemical fertilizers for lawns, gardens and agriculture.

 The increase, while small, is significant, since a molecule of N 2 O can

absorb 320 times more heat than a molecule of CO 2 , making it a

substantial contributor to global warming

 Moreover, N 2 O can further exacerbate global warming through

deforestation resulting from acid rain.

 Finally, as a pollutant, N 2 O contributes to urban smog.

Danger in the Air

Sulphur Dioxide (SO2)

fossil fuels.

indirectly to global warming through deforestation brought