EARTH’S ATMOSPHERE,

PAST AND PRESENT

1. Introduction

2. Evolution of Earth’s atmosphere

3. Present-day composition

4. Atmospheric density and pressure

5. Atmospheric structure

6. Air pollution

Earth’s atmosphere: a thin envelope of gases.

Source: Christopherson, 2009, p. 63.

Earth’s atmosphere: a thin envelope of gases.

Source: Weber State University HARBOR balloon flight, August 2009.

Age

(bn. yrs BP)

Composition Features

4.6 to 4.0 H2O, HCN, NH3,

CH4, S, Cl, others

Primary atmosphere, lost to

space

4.0 to 3.3 At 4.0: H2O, CO2,

N2, S, hydrocarbons,

little/no free O2

Outgassing; anaerobic.

At 3.6: chemosynthetic

bacteria

3.3 to 0.6 At 3.0: CO2, H2O,

N2, <1% O2

Outgassing

At 3.3: first photosynthesis

in cyanobacteria

0.6 to present Today: 78% N2, 21%

O2, 0.9% Ar, 0.036%

CO2, trace gases

Gradual development of

atmosphere; abundance of

LIFE

EVOLUTION OF EARTH’S ATMOSPHERE

(Source: After Christopherson, 1997)

The GAIA hypothesis, formulated by

Jim Lovelock in the 1970s and early ’80s

Basic concepts:

• The Earth is ‘alive’, that is, functions as

one enormous organism

• Consequently, the Earth’s biosphere helps

regulate conditions to keep conditions

suitable for itself

Formation of Earth

and the solar system Present day

The Faint Young Sun Paradox

4 3 2 1 0

Billion years BP

0.8

0.9

1.0

1

10

100

1000

CO2

relative to

present Temp.

(K)

320

230

140

Solar luminosity

relative to present

The ‘faint young sun’ paradox. Source: Frakes, et al., 1992.

Evolution of Earth’s atmosphere over

billions of years shows that

composition is DYNAMIC, not static,

i.e. it can and does change over time.

Components of the Lower Atmosphere (% dry air)

Oxygen

Nitrogen

Others

Oxygen 21

Nitrogen 78

Others 1

Argon 0.93

CO2 0.03

Others 0.04

ATMOSPHERE

BIOSPHERE

LITHOSPHERE

HYDROSPHERE

The ecosystem

concept: biotic

and abiotic

components. Source: Christopherson,

2012, p. 558.

Producers

Consumers

Decomposers

Nutrients

Carbon dioxide cycle. Source: Christopherson, 2012, p. 566.

On time-scales less than billions of years,

atmospheric composition changes less

dramatically, but still changes, especially

concentrations of gases such as carbon

dioxide and methane.

These changes are natural over relatively

longer time-scales (100,000 year cycles), but

recent evidence suggests humans have

affected the composition of Earth’s

atmosphere since the industrial revolution

(roughly 1850).

Atmospheric carbon dioxide concentrations

over the last 1000 years. Source: IPCC, 1996.

Car

bon d

ioxid

e co

nce

ntr

atio

n (

ppm

)

Years before

present

Source: data from WDC Paleoclimatology and NOAA Mauna Loa CO2 records.

Couldn’t this all be part of a natural cycle? Atmospheric CO2 recorded in the Vostok ice core, Antarctica, and

measured at Mauna Loa, Hawaii.

Recent carbon

dioxide

increases in the

context of the

last 1000

years.

Source: Christopherson,

2012, p. 285; Arctic Climate

Impact Assessment, 2004.

Atmospheric carbon dioxide concentration recorded at

Mauna Loa, Hawaii. See Christopherson, 2012, p. 64.

300

310

320

330

340

350

360

370

380

390

400

1958 1968 1978 1988 1998 2008

Atm

os

ph

eri

c c

arb

on

dio

xid

e (

pp

m)

Year

Data source: NOAA Earth Systems Research Laboratory, http://www.esrl.noaa.gov/gmd/ccgg/trends/.

Trends in atmospheric carbon dioxide

concentration over the last 800,000 years.

Source: NOAA Earth Systems Research Laboratory, http://www.esrl.noaa.gov/gmd/ccgg/trends/history.html

Atmospheric methane concentrations. Source: IPCC, 1996.

Global average temperature change over the last 140 years.

Source: IPCC, 2001.

Global average temperature change over the last 140 years.

Source: The heat is on, The Economist, 2011.

Global average temperature change over the last 1000 years. Source: IPCC, 2001.

Recent carbon

dioxide

increases in the

context of the

last 1000

years.

Source: Christopherson,

2012, p. 285; Arctic Climate

Impact Assessment, 2004.

Source: Christopherson,

2012, p. 62.

Height

in miles

Height in

kilometres

Atmospheric

pressure in millibars

Sourc

e: C

hri

stopher

son,

2012, p.6

2.

Height

in miles

Height in

kilometres

Temperature

Troposphere

Stratosphere

Mesosphere

Thermosphere

Sourc

e: C

hri

stopher

son

, 2012, p61.

Normal lapse rate.

Source: Christopherson, 2012,

p. 66.

The atmosphere as

a protective filter.

Source: Christopherson, 2012, p. 66.

Space shuttle Endeavour viewed from the International

Space Station. Source: Eos volume 92 number 50, p. 471, 13 December 2011

Troposphere

Stratosphere

Mesosphere

Smog in the Wasatch Front/Salt Lake City area.

Source: Salt Lake Tribune, 2002.

Smog in the Wasatch

Front/Salt Lake City

area, during and after

an inversion.

Source: Salt Lake Tribune, 2007.

County Grade

Cache C

Weber F

Davis F

Salt Lake F

Utah F

Utah air quality

grades 2007 for

ozone (24-hr).

Source: American Lung Association.

County Grade

Cache F

Weber F

Davis F

Salt Lake F

Utah F

Utah air quality

grades 2007 for

particulates (24-hr).

Source: American Lung Association.

Formation of

photochemical

smog. Source: Christopherson, 2012, p. 74.

Air pollution and mixing in the atmosphere:

the effects of inversions. Source: Christopherson, 2012, p. 72.

Air pollution and mixing in the atmosphere:

the effects of inversions. Source: Christopherson, 2012, p. 72.

Atmospheric concentration of CFC-11. Source: IPCC, 1996.

Source;

Christopherson,

2009, p. 71.

Source; Christopherson, 2012, p. 69.

Antarctic ozone hole as measured

by NASA TOMS instrument.

Antarctic ozone hole, September 12 2008.

Source; Christopherson, 2012, p. 68.