Why do tyres crack between the tread?

Cracking in the tyre tread grooves

Cracking between the tread blocks is a typical form of tyre ageing.

Why does it occur in this area first?

The tread grooves are made out of a thinner rubber material so they are more exposed to the elements. UV light, ozone, and various temperature shifts affect these regions first, drying and cracking the rubber in these areas before the ageing process occurs elsewhere on the tyre.

Is it safe to continue driving?

If the cracks are located in the tread grooves and are surface-level, the tyre may still be safe for some time. However, this is something that should be examined by a professional. If the cracks are extensive, deep, or if the cracks reach the sidewall, the tyre may need to be replaced because the structural integrity may be compromised.