Question

Aluminum-26 is an isotope that is commonly used to determine when exactly a meteor fell to earth. While in space, bombardment of cosmic rays creates Aluminum-26 isotopes continually – a process that is prevented by our atmosphere here on Earth. If you found a meteorite with an aluminum content where roughly 93% of the Aluminum-26 has decayed, about how long ago did it fall to Earth?

Answer 1

Aluminum 26 half life t_1/2 = 7.17 x 10⁵ years

Decay constant λ = 0.693/7.17 x 10⁵ = 9.67 x 10^-7 years^-1

N = N_oe^-λt

N = N₀ - 0.93N_o = 0.07N_o

0.07N_o= N_oe^-λt

0.07= e^-λt

1/0.07 = e^λt

e^λt = 14.286

λt = log_e14.286

t = log_e14.286/λ

t= 2.659/9.67 x 10^-7 = 2.75 x 10⁶ years

around 2.75 million years ago that meteorite fell to earth