radioactive elements help (urgent)

[amyskinner]

Amongst the radioactive elements that were incorporated when the Earth was formed were:

uranium 238U with a half-life of 4.5 � 109 y

uranium 235U with a half-life of 7.1 � 108y

thorium 230Th with a half-life of 8.0 � 104 y

iron 60Fe with a half-life of 1.5 � 106 y

manganese 53Mn with a half-life of 3.6 � 106 y

thorium 232Th with a half-life of 13.9 � 109 y


Given that the Earth is believed to have been formed 4600 Ma ago, which of the above isotopes could still be contributing to the radioactive heating of its interior? Could you please give a brief explanation of your reasoning. Thanks.