IB Biology HL A2.1.8 Dating First Cells and Luca Questions

Describe how radiometric methods date fossils and surrounding rocks. Explain how molecular clocks use changes in DNA or proteins to estimate divergence times, and that LUCA may have existed around 4 billion years ago.

Exam points

Describe how radiometric methods can date fossils and the rocks surrounding them.
Explain how DNA or protein changes in molecular clocks estimate divergence times and that LUCA may have existed around 4 billion years ago.

[Maximum number: 2]

Outline the methods used for dating fossils and rocks using ${ }^{40} \mathrm{~K}$ .

${ }^{40} \mathrm{~K}$ decays into ${ }^{40} \mathrm{Ar}$ ;
ratio/proportion of ${ }^{40} \mathrm{~K}$ to ${ }^{40} \mathrm{Ar}$ indicates the age of the rock/fossil;
half-life of ${ }^{40} \mathrm{~K}$ is 1250 million/ 1.25 billion years;
${ }^{40} \mathrm{~K}$ can (only) be used to date very old samples/older than 100 000 years;

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IB Biology HL A2.1.8 Dating First Cells and Luca Questions question 1