The oldest rock on Earth
A grey outcrop in northern Canada survives four billion years — and ends the Hadean.
- When
- Known to
- ± 3 million years
- Era
- Hadean
The Acasta Gneiss in the Northwest Territories formed as an igneous rock about 4.031 billion years ago and was later metamorphosed. Unlike the Jack Hills zircons, which are isolated crystals recycled into younger sandstone, this is intact rock still in place. Its age defines the boundary between the Hadean and the Archean: from here Earth has a continuous rock record.