<h1>Solar System</h1>
<h2>Dating</h2>
<ul>
<li>Counting craters</li>
<li>Radiometric dating</li>
<li>Measuring proportions of <a href="/second-brain/atom">atom</a>s and isotopes in solidified rock
<ul>
<li>E.g. <a href="/second-brain/potassium">potassium</a>-40 decays into <a href="/second-brain/argon">argon</a>-40</li>
<li>Parent decays into daughters</li>
<li>Decay has a half-life
<ul>
<li>Time it takes for <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mfrac><mn>1</mn><mn>2</mn></mfrac></mrow><annotation encoding="application/x-tex">\frac{1}{2}</annotation></semantics></math>21​ of the sample to decay</li>
</ul>
</li>
</ul>
</li>
</ul>
<a href="/second-brain/astronomy">Astronomy</a>

Solar System

Dating

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