* Half-life: Potassium-40 has a half-life of 1.25 billion years. This means it decays at a relatively slow rate, making it suitable for dating older rocks.
* Dating Range: While K-40 can date rocks much older than one million years, its decay rate is slow enough to provide accurate results for this age range.
* Abundance: Potassium is a common element found in many rocks, making it readily available for dating.
* Decay Products: K-40 decays into both argon-40 (Ar-40) and calcium-40 (Ca-40). The accumulation of Ar-40, which is a gas, in the rock can be measured to determine the age.
Other isotopes might be considered, but they have limitations:
* Carbon-14: This isotope is only useful for dating organic materials up to around 50,000 years old.
* Uranium-238: While uranium dating is suitable for older rocks, its half-life (4.5 billion years) is too long to provide accurate results for a rock layer only one million years old.
Therefore, potassium-40 is the most suitable isotope for dating a rock layer estimated to be around one million years old.
