The outer layer of cells in an early embryo is called the trophoblast.

The trophoblast is responsible for:

* Implantation: Attaching the embryo to the uterine wall.

* Placenta formation: Developing into part of the placenta, which provides nutrients and oxygen to the developing fetus and removes waste products.

It's important to note that the trophoblast is distinct from the inner cell mass, which will eventually give rise to the embryo itself.