Calculating Ages of Solar System objects Radiometric dating Cratering Sequencing

____________________ using radioactive decays P D Parent Element Daughter Element Half-life – __________________________________________. Examples of radioactive isotopes - ________________ half-life = 4.5 Gyr 232Th half-life = 3.5 Gyr ____ half-life = 6,000 yrs (Carbon dating) See also pages _______ for more on radiometric dating!

Fill this in based on the next slide. Number of half lives Time (years) Number of Parents Fraction parents still left Number of Daughters # Daughter/ # Parent 1 2 3 4 5

Radioactive Decay, cont. Assume we’re doing Iron-60 dating. It has a half-life of 5 million years Radioactive Decay, cont. At time = 0, the rock formed 1 half-life later… ______ yrs total Clicker question now After 2 half-lives ______ yrs total After 3 half-lives ______ yrs total 4 half lives ______ yrs total 5 half-lives ______ yrs total After 6 half lives …

How many parents are left after 2 half lives? 8 zero 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

Do you think Carbon dating is effective for a 1 million year old fossil? Yes No Why or why not? ___________________________________________________________________ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

5 million years 10 million years 20 million years 30 million years Element P decays into element D with a half-life of 10 million years. You find 3 times as many daughters as parents. (D/P = 3) How old is the rock? 5 million years 10 million years 20 million years 30 million years 40 million years I have no clue 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

3,000 years 6,000 years 9,000 years 12,000 years 18,000 years You find an animal skeleton that has 1/8th as much carbon-14 in it as living samples have. How old is the skeleton? 3,000 years 6,000 years 9,000 years 12,000 years 18,000 years 24,000 years 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

Radiometric dating Any questions? ______________ dating __________: ____________________________ if using __ Radioactive dating Radioisotope dating. I won’t call it by these names. These names won’t be on your test.

Review: Simplified History Formation - _____________ ago Present ______________________________ _________________________________ Recall: 1 Gyr = ___________________ This history was determined by _____________________ ________________________! How old are the planets in the solar system? Note: the Sun is ________ years old. It’s ______ burned out. How much longer will it last?

Crater Formation Before ______________! Why is 11 km/sec minimum? Rocky or icy objects (also called ___ & ___ ) This is going to leave a mark… Impact site’s ground gets vaporized. So does the impactor!

Craters An object this size Will make a crater this big! Diameter of crater is about ______diameter of rock. Depth of crater is about _________the diameter of rock. See also p. ____

Crater _____ These streaks of ejecta are called “_____”. ________________________________ over about _____________ years because _____________________ chemically alters them. Most prominent under _______________ (at what time, locally?). So, how can you find the youngest craters on the Moon? rays

Crater Sizes Small < 25 km Big - up to 200 km Note the central peaks This puppy is the size of the L.A. basin! And…

REALLY HUGE!! Also known as “multi-ring impact basins” Similar, but a bit larger crater formed on Mercury, and on the opposite side, we see “weird terrain” see page ____. That just had to hurt. Big crater on the Moon

How do we measure ages? Relative dating – Principle of Superposition Ordering of events based on appearance. Crater counts – surfaces with _______________ are new or old? Why? (see p. ____________) Radiometric dating of rocks. (see also section 8.5) Called “Carbon dating” when used on recent fossils.

Relative Surface Dating – Can you order the events? A. Volcanic Eruption B. Fault C. Crater D. Hills Cratered Terrain (Hint: old or new? Created when?) F. Crater G. Crater

A Real Example - Iapetus What can you say about the age of the small crater? Landslide? Smaller Crater Iapetus is one of Saturn’s moons. Picture taken by Cassini Crater Rim Scarp (Shrinkage quake) & subsequent landslide There is cratering on ground. Do you see many or few craters in this big crater? What does that tell you about the circled crater? Is old or new?

Iapetus – entire moon Diameter = 1460 km Here’s the “big crater” we just looked at. Approx 500 km across Landslide is here. Ridge all along equator. Mystery! In Fall 2009 – the light/dark hemispheres mystery was solved.

Ages Now you know how astronomers calculate ages. Study for the last test. It is NOT cumulative.