Reasons for Seasons (recap)Revolution (around the sun)

Rotation (on its axis)

Earth’s Tilt

Axial parallelism

Sphericity

The Earth’s tiltperpendicular to plane of

equator

Q: do these planes form great circles?

Arctic Circle as viewed from above the plane of the ecliptic

Credit: www.physicalgeography.net

24 hrs day

24 hrs night

the parallel of the Arctic Circle is set by Earth’s tilt

equinox June 21

the circle of illumination divides the earth equally into day and night halves - it forms a great circle-

note that 1/2 of earth is always in the light

March of the Seasons

earthyear.mov

Earth’s Modern Atmosphere

Chapter 3

note: relative size of atmosphere not to scale

The atmos-“spheres”

How much atmosphere is there?

How thick is the atmosphere?The atmosphere is incredibly thin - if Earth were the size of a 12” globe, 99% of its atmosphere would be

about as thick as the paint on this globe!

the total mass of the atmosphere is 5.3x1018 kgBUT mass ocean = 1.4x1021 kg

& mass Earth = 6x1024 kg

The atmosphere is crucial to lifeanalogous to a cellular membrane, regulating

what can enter (such as filtering UV rays)

Cre

dit:

http

://w

ww

.u.a

rizon

a.ed

u/ic

/nat

s101

1/le

ctur

es/c

h02/

FIG

02_0

20.J

PG

air is a mixture of nitrogen and

oxygen with some trace

gases

What is air?

average density of air is 1.3 kg/m3

Evolution of the Atmospherethe present composition of the atmosphere represents

the net sum of many processes (biological and chemical) operating over 100’s of millions of years

if Earth were lifeless, its atmospheric composition

would be very different (for example, no oxygen)

*Probable early atmosphere: CH4, H2, H2O, NH3

*Early Evolution H2 is lost H2O photochemically disassociates H2 is lost CH4 + O2 CO2 + H2O NH3 + O2 N2 + H2O CO2 reacts to form CaCO 3

*3.5 by: N2, CO2, H2O (mostly N2) Photosynthesis and oxygen Fe is oxidized, last banded iron

*2 by to present: evolution of the modern atmosphere

Earth’s atmosphere in the distant past

Stomatapores on leafs

Troughton and Donaldson 1972

atmospheric oxygen (O2) is produced by photosynthesis

6CO2 + 12H2O C6H12O6 + 6H2O + 6O2light

CO2

O2

From World Book © 2002 World Book, Inc., 233 N. Michigan Avenue, Suite 2000, Chicago, IL 60601. All rights reserved. World Book illustration by James Teason

carbon dioxide + light => sugars + oxygen

phytoplankton in oceans

www.ekologija.net/ zajednicki/phytoplankton.jpg

most atmospheric nitrogen (N2) is produced by volcanoes

the other relatively abundant gas, argon (Ar), is inert (not reactive)

and not involved in biological processes

- produced by radioactive decay of 40K

atmospheric carbon dioxide (CO2) is produced and released by terrestrial photosynthesis and

respiration, as well as air-sea gas exchange

atmospheric water vapor (H2O) varies tremendously (from <1 - 4%

by volume) and is affected by evaporation and condensation

air density decreases with height in the atmosphere because of gravity

pressure decreases rapidly with altitude

Credit: http://www.physicalgeography.net

elevation of Mt. Everest

~30% of sea level

elevation where jets typically fly

~20% of sea level

average tropopause elevation

~10% of sea level

the atmosphere has several layers

with distinct properties and

functions

think of these layers as

concentric shells orsphereswe can

characterize vertical profiles

according to three criteria

Troposphere

StratosphereTropopause

over 99% of the atmosphere is contained in the troposphere and

stratosphere

Layers classified by temperature

the tropopause elevation (and thus the thickness of the troposphere) varies with latitude

the tropical tropopause is twice as high as the polar tropopause because of vigorous

surface heating at low latitudes

Cre

dit:

http

://ap

ollo

.lsc.

vsc.

edu/

clas

ses/

met

130/

note

s/ch

apte

r9/g

raph

ics/

trop_

hgt.f

ree.

gif

Cre

dit:

ww

w.p

hysi

calg

eogr

aphy

.net

90% of atmospheric

mass ~5x10^18

kg

why does T decrease

with height in troposphere?

why does T increase with height in the stratosphere

?