1. Radiometrc Dating and Aging our Solar System
How do we know how our solar system formed?

2. Learning Target
Describe how the age and composition of Earth’s oldest rocks, lunar rocks and meteorites are determined by radiometric dating.

3. What is radioactivity
The Breakdown of Unstable Nuclei

4. What is radiometric dating?
Used to determine the absolute ages of rocks.
Let’s read about it!!
Highlight the Guide for Reading Questions
Create notes in your notebook.

6. Using Half-lives to determine ages of rocks
Half-life is the time it takes for half of the mass of a radioactive isotope to decay.
Let’s do an activity to help us understand!!
Define Half-life in your notes

9. All isotopes decay at a known rate and certain ones are useful in dating rocks.

10. Let’s try some practice problems!!!

11. Why do we care?
The age of meteorites tell us about the age of planetary accretion
The age of rocks in Mars’ craters can tell us about the period of heavy bombardment.
The age of lunar rocks can tell us about Moon’s formation.
The age of Earth’s oldest rocks can tell us about planetary cooling.

12. Solar System Samples Meteorites
Bottom line – meteorites tell us about the composition and processes that took place to form our Solar System
Some are unaltered – give us dates and composition (and process)
Some are altered – process information (metamorphism, differentiation) (and composition)
Some come from different places within a planet – again, composition and process
Meteorites and their message
- Meteorites are bits of solar system that enter earth's atmosphere. Most burn up from friction (never hit). ~500/year baseball-sized.
- Rare bigger ones hit, including a big one about 65 Ma (10 km diameter in Mexico).
- Big ones cause local melting of any rocks that they hit. Explosive craters.
5 types: Stones, irons and stony-irons: DESCRIPTION
1) Chondrites - 79% - most common
- tiny balls (chondrules) of mafic minerals formed by rapid cooling.
- Age = 4.6 Ga. Oldest rocks of solar system.
2) Carbonaceous Chondrites - 5% - chondrites, plus minor organic compounds such as amino acids.
- Composition same as Sun (for non-volatile elements like C, Si, Al, Fe, Mg).
3) Achondrites - 8% similar to terrestrial mafic igneous rocks, some with brecciated texture.
4) Iron Meteorites - 6% - intergrowths of iron-nickel alloys.
- Large crystals indicating slow crystallization.
5) Stony-irons - 2% - mixture of iron-nickel and silicate minerals.
5 types: INTERPRETATION
1) Carbonaceous Chondrites - chondrites + carbon.
- Represent protoplanetary material formed at condensing of the solar nebula and never remelted.
2) Iron Meteorites - iron-nickel alloys.
- Core of differentiated protoplanets.
3) Achondrites - mafic igneous rocks, some brecciated.
- Represent somewhat younger pieces of igneous rocks produced on larger asteroids.
4) Stony-irons - mix: iron-nickel and silicate minerals.
- Interpreted to represent the transition zone between an iron-nickel core and a silicate mantle.
5) Chondrites - mafic silicates formed by rapid cooling.
- May represent crystallization as drops from melted silicates as a result of asteroid collisions in the accretionary phase.
Will Eros hit Earth?
Not anytime soon. Using telescope-mounted digital cameras, NASA researchers have found more than 350 near-Earth asteroids larger than 1 kilometer (about 0.6 miles) in diameter. From this information they estimate anywhere from 500 to 1,000 similar-sized NEAs could be spinning around our solar system. Good news is the scientists say none of the asteroids they’re tracking will hit Earth in the near future. In addition, what the NEAR mission learns about Eros will help scientists if they ever do spot an asteroid headed our way.
Dawn's goal is to characterize the conditions and processes of the solar system's earliest epoch by investigating in detail two of the largest protoplanets remaining intact since their formations. Ceres and Vesta. The top level question that the mission addresses is the role of size and water in determining the evolution of the planets. Ceres and Vesta are the right two bodies with which to address this question, as they are the most massive of the protoplanets, baby planets whose growth was interrupted by the formation of Jupiter. Ceres is very primitive and wet while Vesta is evolved and dry. The three principal scientific drivers for the mission are first that it captures the earliest moments in the origin of the solar system enabling us to understand the conditions under which these objects formed. Second, Dawn determines the nature of the building blocks from which the terrestrial planets formed, improving our understanding of this formation. Finally, it contrasts the formation and evolution of two small planets that followed very different evolutionary paths so that we understand what controls that evolution.
Image:
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13. Let’s put everything together!!
Universe: 13.8 billion years ago
Solar system: 4.6 billion years ago
Earth as a planet: 4.5 billion years ago
So how did we get to where we are today?
Geologic Timescale!!

14. Geologic Timescale