Lecture 5: In the Beginning: Radiometric Dating

1. The Age of the Earth2. Radiometric dating - early chronology

Meteorites - the stories they tell

• The Meteorite “Allende” (fell in 1969, Mexico)is ~30 Ma olderthan the Earth,and has isotopesfrom a Supernovathat exploded~4.60 Ga ago !

The Oldest Rocks on Earth

• The age of our Sun Sun’s age = 4 560 million years (= 4.56 Ga) helioseismology

• The age of our Earth Earth’s age = 4 530 million years radiometric dating of rocks

The Formation of the Earth

• Precise timeline of early events.

Radiometric Dating

• Radioactive 40K decays to 40Ar. Half-life: 1.25 Ga.

The Periodic Table

Radiometric Dating

Radiometric Dating

• Radioactive 238U decays to 206Pb. Half-life: 4.5 Ga.

Radiometric Dating

• This zircon is 3.458 Ga old, and so are the rocks in which it was.

Main points to take home:

1) The Earth formed ~30 Myr after the Sun, about 4 530 Myr ago

2) Radioactive decay - a reliable chronometer.