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Astronomy 3040
Astrobiology
Spring_2016
Day-8
Project
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Course Announcements
•
•
Colloquium on Friday, Feb. 19. @2:30pm B310
Dr. David James, Cerro-Tololo InterAmerican Obs.
•
Open Clusters, Stellar Evolution and Calibrating the Ages
of Stars: Blanco 1
•
Galactic open clusters are laboratories, provided by nature, for
us to study stellar evolution. Using 1m-, 4m- and 8m-class
telescopes, I will show how spectroscopic and photometric
observations of solar-type stars in open clusters allow us to
establish a stellar chronometer, and create an age-ranking
system for an ensemble of nearby, well-studied clusters. With
the aid of new observations of Blanco 1, an high-Galactic
latitude, Pleiades-age cluster, I will show how deriving stellar
age must be based upon very high quality observational data
and a diverse range of stellar models.
Today
 § 3 HW – 6, 8, 16, 18, 38, 55, 56, 58, 60, 65
 Due Monday Feb. 22
 1st quarter observing session
 7:30pm tonight
Homework
 Due Wed. Feb. 24
 Chapter 4:

3, 9, 18

21, 27, 32

37, 42, 46

49, 50, 54
Chapter - 4
 Geology & Life

Earth is unique within our solar system
Moderate Temperatures (slight greenhouse effect)
Abundant water
Protective atmosphere
Relatively stable environment
 Contrast Moon, Mercury, Venus, Mars (Fig 4.1)

Distance from Sun

Volcanism & Plate Tectonics

Magnetic field
Mercur
y
Moon
Mar
s
Venu
s
The History of Life on Earth
 Geological Record – fossils and rock layers

3 basic types of rock (Fig 4.2)
Igneous – molten rock that cools and solidifies

Basalt,Granite
Metamorphic – transformed under
Pressure/Temperature

Marble, Slate
Sedimentary – gradual compression of sediments



Important to fossil studies – slow buildup with fossils.
Limestone, Sandstone
Rock Cycle (Fig 4.3) + 4.4, 4.5, 4.6
The History of Life on Earth
 Rock Analysis

3 basic types of rock
Mineralogical – identify minerals in the rock
Chemical – determine the elemental composition
Isotopic – ratio of different isotopes - gives formation age

Radioactive Dating (Fig 4.7)
Half-life – probability (Fig 4.8; Table 4.1; Example 4.1)



Parent – Daughter isotopes
Compare with geological record
Sometimes, find organic material (Jurassic Park) (Fig. 4.9)
The Geological Time Scale
Al26
Mg26 is important for
early heating of Earth's core.
The History of Life on Earth
 4 Eons (Fig 4.10)

Hadean - “Hellish”

Archean - “Ancient Life”

Proterozoic - “Earlier Life”

Phanerozoic – Visible Life”
 Age of the Earth – oldest rocks 4.0 Gyr

“Zircons” (Fig 4.11) ~4.4 Gyr
Suggest the crust separated from interior ~4.5 Gyrs

Moon rocks ~4.4 Gyr
Therefore, Moon existed by this time.
Hadean Earth, Dawn of Life
 3 generations of atmospheres

Primary – H, He
Planet formation

Secondary – CO2, H2S, SO2, H2O...
Outgassing (Fig 4.12), Comet delivery(?)

Tertiary – N2, O2, H2O
Modified by life
Hadean Earth, Dawn of Life
 Late Heavy Bombardment – ~3.9 Gyr ago

Relatively quiet between formation and LHB

Since then, protected by Jupiter
 Sterilizing Impacts

350-400 km in diameter (Fig 4.13)
Completely vaporize the oceans
Global surface temperature rise 2000 C (3600 F)
Last ~4.2-3.8 Gyr ago
Impact Energies
and these are the
small ones
Geology & Habitatbility
 Earth's Interior – Seismic waves (Fig 4.14)

Crust – lowest density, Al, Si, Ca

Mantle – rocky “plastic”

Outer Core – molten

Inner Core – solid, Fe, Ni
 Earth's Interior – Differentiation

Melting and sedimentation of heavy material to core

Al26 ==> Mg26 contributed a lot of early heat
Geology & Habitatbility
 Plate Tectonics (Fig 4.15)

What is it?

What causes it?
 Evidence

Continental edge fits (Fig 4.16)

Seafloor spreading

Two types of crust
Seafloor crust – young, high density basalt, thin
Continental crust - old, lower density granite, thick
 Figs 4.18 - 4.23
Magnetic Field
 Loss of Atmosphere

Thermal escape – light favored over heavy

Impacts

Solar wind stripping
 Cause

Electrically conducting interior fluid layer

Convection in the fluid layer

Moderate to fast rotation (dynamo effect)
 Figs 4.24 - 4.25
Magnetosphere & Solar Wind
 Magnetosphere

Protects surface and atmosphere from direct impact

Van Allen Belts
Trapped charged particles
Directed down to earth at poles