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.