Complex sentence: The most stable of californium's twenty known isotopes is californium-251, which has a half-life of 898 years; this short half-life means the element is not found in the Earth's crust.
Split into simpler sentences: The most stable of californium's twenty known isotopes is californium-251, which has a half-life of 898 years. This short half-life means the element is not found in the Earth's crust.