Please read the following table in HTML format from a webpage and then answer the question in detail according to the table. Each table cell is defined by a <td> and a </td> tag. Each table row starts with a <tr> and ends with a </tr> tag. 'rowspan=m' and 'colspan=n' represents a cell spaning over 'm' rows and 'n' columns.

Webpage title:
Earth
Table title:
Heat
Table:
<table id='hittask' contenteditable='False'>
<tr> <th colspan=1 rowspan=1 > Isotope </th><th colspan=1 rowspan=1 > Heat release W/kg isotope </th><th colspan=1 rowspan=1 > Half-life years </th><th colspan=1 rowspan=1 > Mean mantle concentration kg isotope/kg mantle </th><th colspan=1 rowspan=1 > Heat release W/kg mantle </th></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=1 > 238U </td><td colspan=1 rowspan=1 > 94.6×10−6 </td><td colspan=1 rowspan=1 > 4.47×109 </td><td colspan=1 rowspan=1 > 30.8×10−9 </td><td colspan=1 rowspan=1 > 2.91×10−12 </td></tr>
<tr> <td colspan=1 rowspan=1 > 235U </td><td colspan=1 rowspan=1 > 569×10−6 </td><td colspan=1 rowspan=1 > 0.704×109 </td><td colspan=1 rowspan=1 > 0.22×10−9 </td><td colspan=1 rowspan=1 > 0.125×10−12 </td></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=1 > 232Th </td><td colspan=1 rowspan=1 > 26.4×10−6 </td><td colspan=1 rowspan=1 > 14.0×109 </td><td colspan=1 rowspan=1 > 124×10−9 </td><td colspan=1 rowspan=1 > 3.27×10−12 </td></tr>
<tr> <td class="highlighted"  colspan=1 rowspan=1 > 40K </td><td colspan=1 rowspan=1 > 29.2×10−6 </td><td colspan=1 rowspan=1 > 1.25×109 </td><td colspan=1 rowspan=1 > 36.9×10−9 </td><td colspan=1 rowspan=1 > 1.08×10−12 </td></tr>
</table>
Question:
Which isotopes in the Earth are heat-producing?
Answer:
The heat-producing isotopes in the Earth are potassium-40, uranium-238, and thorium-232.