As far as I understand earth will inevitably become similar to mars: as the earths core cools down and solidifies our magnetic field begins to disintegrate, seismic and volcanic activities will disappear which ultimately will thin out our atmosphere to a point where life will be impossible. We talking billions of years ofc.

According to science only half of earths internal heat stems from radioactivity, the rest being primordial heat. This in turn means our planet is obviously much cooler than it used to be.

https://www.science.org/content/article/earth-still-retains-much-its-original-heat