Image source: http://www.nasa.gov/mission_pages/stardust/main/index.html

• First sample return mission in 34 years

• Traveled ~ 3 billion miles

• Retrieved samples of comet Wild-2

• Flew through the comets tail

• Collected dust particles in aerogel

StardustStardust

Image source: http://www.nasa.gov/mission_pages/stardust/main/index.html

Image source: http://www.nasa.gov/mission_pages/stardust/main/index.html

Image source: http://www.nasa.gov/mission_pages/stardust/main/index.html

Image source: http://www.nasa.gov/mission_pages/stardust/main/index.html

Geologic TimeGeologic Time

Image source: http://www.nasa.gov/mission_pages/stardust/main/index.html

Image source: http://www.nasa.gov/mission_pages/stardust/main/index.html

• Fundamental geologic observations

• Relative vs. absolute dating

• Economic implications

• Philosophical dimensions

• Earth’s place in the Solar System

• Meteorites

Geologic TimeGeologic Time

• Nicolaus Steno (1669)– Observations regarding sedimentary rocks

• Principle of Superposition• Principle of Original Horizontality

• Principle of cross-cutting relationships– Developed for dating igneous rocks

• Law of Faunal succession (~1800)– Allows correlation of rocks of same age

Relative dating techniquesRelative dating techniques

Principle of Original Horizontality (Grand Canyon, USA)

Source: © The McGraw-Hill Companies, Inc./Doug Sherman, photographer.

Principle of Superposition (Grand Canyon, USA)

Schist and Granite

Source:Courtesy of Carla W. Montgomery.

• Still many unanswered questions…– Absolute age, length of geologic processes

“The Present is the Key to the Past”James Hutton, late 18th century

UniformitarianismUniformitarianism

Source: © The McGraw-Hill Companies, Inc./Doug Sherman, photographer.

Age of the EarthAge of the Earth

• How old is the Earth?

Bishop Usher (16th century)Bible…..~6,000 years old (4004

BC)

Lord Kelvin (19th century)Cooling…20-40 million years old

John Joly (1899)

Salinity of oceans…100 million

Age of the EarthAge of the Earth

RadioactivityRadioactivity

• Radiometric Dating Radioactive isotopes in rocks decay at a known rate

U, Rb, K, Th, C, others….

• Counting atoms in the rocks tells timeParent-daughter ratio

• Concept of half-lifeHow long it takes for half the parent isotope to decay

Parent-daughter ratios become smaller in timeIsotope clocks are useful for ~ 7 ½ lives

Age of the EarthAge of the Earth

• Carbon14N 14C in the atmosphere, then we eat the carbon14C isotopic half-life = ~6,000 years

• U-Pb238U 206Pb, and 235U 207Pb238U isotopic half-life = ~4,500,000,000 years4.5 billion years old (4.5 byo)

• Other ‘old’ isotopic clocksRb Sr, K Ar, Th Pb

Absolute dating: isotopic clocksAbsolute dating: isotopic clocks

• Meteorites ~ 4.57 byo• Earth ~ 4.56 byo• Oldest rocks on Earth ~ 4.0 byo• Oldest minerals ~ 4.4 byo• Oldest sediments ~ 3.8 byo• Oldest fossils ~ 3.5 byo

Billions, not millions!

A very old Earth…A very old Earth…

50 um

The Oldest Minerals on Earth: Zircon (ZrSiO4)

• Subdivisions of geologic time– Eon, Era, Period, Epoch

– Eons• Precambrian: 4.5 b.y. to ~0.5 b.y.

• Phanerozoic: ~0.5 b.y. to today

Geologic time scaleGeologic time scale

• Subdivisions of geologic time– Eon, Era, Period, Epoch

– Eras• Paleozoic: ~560 m.y. to ~250 m.y.

• Mesozoic: ~250 m.y. to ~65 m.y.

• Cenozoic: ~65 m.y. to today

Geologic time scaleGeologic time scale

• Subdivisions of geologic time– Eon, Era, Period, Epoch

– Today (your lifetime)• Eon: Phanerozoic (~550 m.y. now

• Era: Cenozoic (65 m.y. now

• Period: Quaternary (2 m.y. now

• Epoch: Holocene (10 k.y now

Geologic time scaleGeologic time scale

Image source: http://www.gly.fsu.edu/~salters/GLY1000/12Rock_record_time/Slide27.jpg