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Earth Science and Climate Change Session 2
“The Earth – An Introduction”
Bradley Hubbard-Nelson
Concord Carlisle Continuing Education
Fall, 2014
The earth – such a nice place to be
•  Rather unique circumstances make the earth not
only a habitable planet, but comfortable, bountiful,
magnificent…
o  Distance from the sun, given the sun’s radiated
heat, provide a temperature where we can
have liquid water
o  Size of the earth make the gravitation not too
strong to support us
o  Atmosphere has evolved to be a nice mix of
gasses (shaped by the biosphere)
The Solar System (not to scale)
If the planets were drawn at the correct distance from the sun and each other, they would be tiny dots, impossible to see Brief history of the solar system
•  After the big bang (13 billion years
ago), the solar system originated
around 4.6 billion years ago in the
gravitational collapse of a
molecular cloud
•  The earth and other planets formed along with the
sun when the rotating disc of dense, hot gasses
coalesced into liquid droplets, and solidified as they
continued to cool. Oldest rocks ~ 4.4 billion years old
•  Inner planets (Mercury through Mars), closer to the
sun, formed mostly from elements with relatively
high melting points (Iron, Nickel, Aluminum and
Silicates), while the outer “gas giant” planets
condensed from much more abundant gasses
"ʺProtoplanetary-­‐‑disk"ʺ by NASA -­‐‑ NASA; hKp://origins.jpl.nasa.gov/stars-­‐‑planets/ra4.html. Licensed under Public domain via Wikimedia Commons
Early history of earth
•  Earth’s atmosphere caused probably by volcanic
outgassing, but contained no oxygen, mainly water
(H2O), carbon dioxide (CO2) and nitrogen (N2)
•  Frequent collisions with numerous proto-planets,
allowed the earth and other terrestrial planets to grow
to current sizes
•  Gradual cooling from molten state to form a solid crust,
which allowed continents to form and liquid water to
exist on the surface
•  A glancing collision with a protoplanet suspected of forming the
moon and tilting the earth’s
rotation axis, presumably while the
earth was still molten
The Earth and its Orbit
•  Radius Re = 6370 km (3958 mi) = 6.37 x 106 m
•  Mass Me = 6 x 1024 kg
•  Distance from sun De = 150M km = 1.5 x 1011 m
(93M mi) on average, varies +/- 1.3% (the
“eccentricity”)
Orbit periods of the planets
Kepler (16th century) observed: period
T2 ~ D3
2
!
$ 3
4
π
2
&D
More accurately: T = #
" G * M SUN %
Where G = gravity constant, M is the mass of the
big object you’re rotating around
Planet
Distance
T (Revolution) Radius
T (Rotation)
Mercury 58M km
88 days
2440 km
59 days
Venus
108M km
224 days
6054 km
243 days
Earth
150M km
365.25 days
6370 km
24 hrs
Mars
228M km
687 days
3397 km
24.6 hrs
Jupiter
778M km
11.9 years
71,492 km
9.8 hrs
Pluto*
5913M km
248 years
1137 km
6.4 days
Halley** 90-­‐‑5200M km 75 years
11 km
Comparison with nearby planets
•  The earth is in what is called the Circumstellar
Habitable Zone (“the Goldilocks zone”)
Venus – too hot! 462°C due to dense CO2 atmosphere Mars – too cold! -­‐‑50°C average due to very thin atmosphere Solar radiation
•  Surface area Ae = 4π Re2 = 5.09 x 1014 m2
•  Sun radiation power:
Isun = 3.9 x 1026 W (1 Watt = 1 J/sec)
•  At earth distance, solar power/area is:
! I sun $
2
S0 = #
=
1370W
/
m
2&
" 4π De %
at the top of the atmosphere (absorption ignored)
•  Changes with time:
! De $
S(t) = S0 * #
&
" D(t) %
2
•  Minimum(June): Smin =1333 W/m2
•  Maximum(Dec): Smax =1407 W/m2
•  Solar output varies in time << 1% in ~11 yr solar cycle
Earth’s Rotation
•  One rotation per 24 hour day
•  Velocity at equator V = distance/time
= (2π Re)/(24 hr) = 1668 km/hr (~1000 miles/hr)
•  Rotation plays a role in climate by its effect
on the oceanic and atmospheric
circulations, through the Coriolis effect. For
example:
o  Gulf stream (surface ocean current)
o  Overturning circulation (deep ocean current)
o  Hadley Circulation (tropical air circulation)
o  Mid-latitude eddy’s (our weather patterns)
Latitude and Longitude Spherical polar coordinates:
R-­‐‑ radial distance from earth center (constant)
Θ (theta) -­‐‑ latitude angle [-­‐‑90° to 90°]
Φ (phi) -­‐‑ longitude angle [-­‐‑180° to 180°] zero arbitrary
Degrees subdivided into minutes (x60) and seconds (x3600) Distance between longitude lines gets smaller at high latitude: # 2π *ΔΦ &
LΦ = Re * %
* cosΘ
o (
$ 360 '
Seasons and latitude
•  Declination angle 23.5° gives us seasonal
variability
Length of day
Zenith angle
Season variations from sun’s angle
Intensity as function of zenith angle ζ:
S(ζ ) = S0 * cos(ζ )
ζ
(ignoring absorption by atmospheric gasses)
Total incoming (W/m2)
Noon “Insolation” (at T.o.A.)
1600
1400
Concord
1200
1000
Miami
800
600
Singapore
400
200
0
1-­‐‑Jan
11-­‐‑Apr
20-­‐‑Jul
Date
28-­‐‑Oct
Earth’s water (the “hydrosphere”)
•  Earth’s surface mostly covered with water (71%) which
scientists think came with asteroids and comets
•  Ocean typical depth 4km (a very thin covering relative
to the earth’s radius 6370km radius (0.06%))
•  Oceans moderate earth’s temperature in the short
and long time scale
Oceans and seas
•  Fresh water only 2.5%
Ice caps and glaciers
Saline groundwater
70% locked in ice
Fresh groundwater
•  Water vapor (0.001%)
Permafrost
Strong climate
Lakes
Atmosphere
influence
Swamps
Rivers
Soil moisture
Biological
Oceans – basic features
•  An incompressible fluid – nearly uniform density,
depending slightly on salt content and temperature
•  Large heat capacity – 1000x that of the
atmosphere – strong but slow effect on climate
•  Salty : typically 3.4% concentration by weight
•  Acidity: pH of 8.1, about 0.1 lower (25% higher acidity)
than pre-industrial value from CO2 absorption
Tropical paradise
Southern Ocean
Sea Surface Temperature •  Varies dramatically with location and time of year
•  Temperature units: °C = 5/9 * (°F-32°) = (°K - 273.15)
H20 based scale: 0°C = freezing, 100°C = boiling
°C °F
0 32
5  41
10  50
15  59
20  68
25  77
30  86
35  97
40  106
0°C
10°C
20°C 30°C
3 layers, by temperature
•  Mixed layer at sea surface, 50-100m depth, winddriven wave mixing, sizable currents (up to 2m/sec)
•  Thermocline, 500-600m thick, large T gradient
•  Abyss, deep layer, cold (0-2°C), very slow currents
(<1m/hr), less well understood and measured
Ocean currents
• 
• 
Wind driven currents, constrained by land masses
Persistent “gyres” - CW in Northern hemisphere,
CCW in southern, separated by equatorial current
Ocean currents play critical role in climate by transporting heat
Count Rumford (1800): “if the water of the ocean … descends to the boKom of the sea, cannot be warmed where it descends,…, it will immediately begin to spread on the boKom of the sea, and to flow towards the equator, and this must necessarily produce a current at the surface in an opposite direction.” First gulf stream map (Ben Franklin)
Ocean current dynamics
•  Fascinating subject of research, involving complex
geophysical fluid dynamics (GFD)
•  Surface currents have “permanent” features and also
chaotic “weather” patterns which last for weeks or
months
NASA/MIT Ocean Current Simulation
Geomorphology – formation and structure of the earth
Layer
Thickness
State
-­‐‑ Ocean floor
7-­‐‑10 km
Solid Si/Mg/Fe
-­‐‑ Continental
20-­‐‑70 km
Solid Si/Al/Fe
Mantle
2900 km
Viscous
Outer core
2200 km
Liquid Fe/Ni
Inner core
1200 km
Solid Ni
Temp
Lithosphere (crust):
•  Magnetic field from fluid flow in the
outer core (“dynamo”), changes with
time and may have had climate
impact;
•  Core heat ~1/2 from radioactive
decay, rest is primordial heat
•  Heat loss through lithosphere ~ factor
of 10,000 less than incident solar
800-­‐‑4000°K
6000°K
Lithosphere movement
•  Thin Lithosphere (‘rocky crust’) divided into continental
plates, floating on earths semi-liquid mantle
•  Important geologic processes occur where plates come
together or separate
•  Earthquakes, volcanos are the external phenomena
Continental Drift – Plate Tectonics •  Continental plates move at speeds of 10 to 40mm/yr
•  Time scale for large movement (1000km) of order:
Time = Distance/speed = 106m/10x10-3m/yr = 100 M yr
• 
• 
Thought to have been one
continent during Cretaceous
period (early dinosaur age)
Continental arrangement
very different than today –
most land in southern
hemisphere
Ocean & land masses
Note distortion on rectangular projection
(Continental US really ~4x bigger than Greenland
Arctic: frozen à
Temperate: wet
à
Sub-­‐‑tropics: dry à
Tropics: very wet à
Sub-­‐‑tropics: dry
à
Southern Ocean
à
Antartic: frozen
à
Distribution of land not uniform
80%
70%
Land fraction
60%
50%
40%
Antartica
90%
Concord
100%
North Pole
Most of the land in northern hemisphere
Continental arrangement plays dominant role
in climate, particularly regionally
Southern Ocean
• 
• 
Land fraction
Area Weighted
30%
20%
10%
0%
-­‐‑90
South
-­‐‑60
-­‐‑30
0
30
Latitude
60
90
North
The Earth’s Atmosphere
•  A thin gaseous skin with multiple layers
•  A compressible fluid
-  Pressure, density fall exponentially with height
-  80% of atmosphere inside 10km
Atmosphere at moon-­‐‑rise from the International Space Station
Atmosphere structure
Four layers, differentiated by the temperature gradient:
Pressure units:
1 atm (sea level) =
1000 hectopascals =
1000 milliBar
The troposphere
and (to a lesser
extent) the
stratosphere are
important for
climate
Tropospheric gas mixture
•  What are these?
•  How did it get this way?
Volume fraction
N2 -­‐‑ Nitrogen (diatomic)
O2 -­‐‑ Oxygen (diatomic)
Ar -­‐‑ Argon (Noble gas)
H2O
CO2
other
Atmospheric constituents
Name
Activity
%
Where from?
Absorption
Respiration of living vegetation, plankton Absorbs visible
N2 Nitrogen Mostly inert
78%
O2 Oxygen Active
21%
Ar Argon
Totally inert
0.9% Radioactive decay of 40K (Potassium)
No absorption
Somewhat
active
0.2-­‐‑ Evaporation, plant 0.5% respiration
Absorbs IR and visible
H2OWater vapor
CO2 Carbon Somewhat dioxide active
0.04% Volcanos and humans (fossil Absorbs 400ppm fuel burning, agriculture, etc) infrared
CH4 Methane Active
1.7 ppm Organic decay
Absorbs infrared
Highly active
500 ppb Exhaust, photoproduced in stratosphere
Absorbs IR and UV
Somewhat active
310 ppb Agriculture
Absorbs infrared
Inert
<1 ppb
Absorbs infrared
O3 Ozone
N2O Nitrous oxide
Freons
Refrigerant, industrial processes
History of the Atmosphere
•  Atmospheric gasses have changed dramatically since
the formation of the earth
•  Strongly influenced by life forms and gradual oxidation
of the lithosphere
•  Early sun was 30% weaker (strong greenhouse effect)
General features of
changing gas
mixture with time
(Source unknown)
Appearance of Oxygen
Stages
0.5
1
3
2
4
5
Atmosphere
P O 2 (atm)
0.4
0.3
0.2
0.1
0
3.8
?
3
2
1
Ga 0
Stages:
1: Practically no O2 in atmosphere
2: O2 produced, but absorbed in oceans & seabed rock.
3: O2 starts to gas out of oceans, but is absorbed by land surfaces.
4 & 5: O2 sinks filled and the gas accumulates.
Modern stromatolites (Shark Bay, Australia): rock structures made of cyanobacteria, which contribute O2 to the atmosphere
• 
Heinrich D. Holland - Oxygenation-atm.svg. Licensed under Creative Commons Attribution-Share Alike
3.0 via Wikimedia Commons
Carbon dioxide (CO2)
•  A trace gas (0.04% by volume), oversized climate effect
•  The “Keeling curve” measured since 1958 started by
Charles Keeling (Scripps institute of Oceanography)
•  Seasonal variation with Northern hemisphere respiration
Currently, more than ¼ of CO2 molecules in the atmosphere was put up there by humans (and will stay for centuries)
Ozone – stratospheric gas, tropospheric pollutant
•  Ozone (O3) created in stratosphere, shields us from
most harmful UV rays
•  O3 in troposphere is a
greenhouse gas (GHG)
•  Stratospheric O3 has
been depleted by long
lived synthetic chemicals
•  Example of coordinated
societal action to solve a
similar atmospheric crisis
Water vapor
•  The most plentiful greenhouse gas (~0.25% typical)
•  Continuously changing with time scale in days
•  Concentration a strong function of temperature,
latitude and altitude
Equator
Concord
Arctic
Parts per thousand by weight
Water vapor and clouds
•  Water exists on earth in all 3 phases (solid, liquid and
gas), so affects climate in numerous ways
•  As vapor, is the most prevalent GHG (warming)
•  Frozen in icecaps and glaciers, it reflects light due to
its low albedo value (cooling)
•  Cooling as air rises, forms clouds of liquid droplets,
blocking sunlight (cooling) and extracting and
releasing energy from the atmosphere and land
General circulation, effect on regional climate
•  Rising air, driven by moisture, cools and expands outward,
causing wet and dry regions in tropics and subtropics
Atmospheric circulation
•  Like the ocean circulation, wind patterns move heat and
affect the climate dramatically
•  Winds driven by pressure gradients (change of pressure
with position) which themselves are due to temperature
gradients
•  Earth’s rotation
causes air to flow
around pressure
H
L
extremes, so-called
“geostrophic flow” –
not from high pressure
to low
Paleozoic era
“Carboniferous”
Mesozoic era
“Dinosaur age”
Proterozoic Eon
Cenozoic era
present -­‐‑ Human predecessors
-­‐‑ Great apes
60 My -­‐‑ Primtes
extinction event
150 My -­‐‑ Birds
130 My -­‐‑ Flowering plants
Archean Eon
200 My -­‐‑ Mammals
extinction event
300 My -­‐‑ Reptiles
-­‐‑ Amphibians
400 My -­‐‑ Insects, seeds
-­‐‑ Land plants
500 My -­‐‑ Fish
-­‐‑ Simple 600 My animals
Eucaryotes (complex cells)
Cyanobacteria, photosynthesis
Prokaryotes (simple cells)
-­‐‑ Earth formed
Appearance of different life forms in geologic record
600 My
present
-­‐‑ Simple animals
1.0 By -­‐‑ Multicellular life
2.0 By
3.5 By
4.6 By
Timeline of life on earth
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Major events
Earth forms 4.6 billion years ago
Life starts (?) 3.8 billion years ago
Age of Bacteria: Archaean era
Oxygen atmosphere: 2 B years ago.
Eukaryotes develop. Proterozoic era
650 M years ago. First multicellular life, forms
unknown today
Cambrian explosion: wide variety of life forms
appear 550 million years ago
Paleozoic era: 550 – 250M years ago. Marine
invertebrates, fishes, amphibians, invasion of land.
Coal formation.
Permian mass extinction: 250 million years ago.
95% of all life dies; end of Paleozoic
Mesozoic: 250-66 million years ago. Age of
dinosaurs (reptiles). Mammals, birds, and
flowering plants
Cretaceous mass extinction: asteroid hits the
Earth, killing much of life, including the dinosaurs.
Cenozoic era: 65 million years ago - present.
Mammals dominant
Cenozoic Era
•  From 65 million years ago,
continues to present.
•  Mammals become the
dominant life form on land.
An “adaptive radiation” that
took advantage of the
sudden loss of dinosaurs.
•  Another large group evolves:
the grasses.
•  Adaptive radiation of birds
and flowering plants.
•  Geologically, continents that
had been separated started
to collide: Africa with Europe,
North America with South
America, India with Asia
Modern period (since dinosaurs)
Climate from Cenozoic era through modern day:
CH4
•  Glacial/interglacial cycles, mostly glacial
•  Holocene may be a typical interglacial cycle
•  Source: National Climatic Data Center (NOAA)
Holocene
Last million years (ice core data)
600ppb
300ppb
CO2
300ppm
NA Ice thicknes
s
200ppm
50M
0M
-­‐‑10C
1000
900
800
700
600 500 400 300 200 100
Time Before Present (Thousands of Years)
0
Global temp
0C