Final answer:
A combination of two or more atoms chemically bound is known as a molecule, and the area where two different ecosystems interact on Earth is called an ecotone.
Step-by-step explanation:
A term that describes a combination of two or more atoms chemically bound together is called a molecule. For example, when carbon atoms join with four hydrogen atoms, they form methane (CH4), a simple organic molecule. Similarly, when two hydrogen atoms form a bond with one oxygen atom, they create a molecule of water, H2O. Atoms form chemical bonds with other atoms by donating, accepting, or sharing electrons to achieve a stable electron configuration.
Regarding the region on Earth where two ecosystems interact, this area is known as an ecotone. An ecotone is a transitional zone between two different ecosystems, where you can find species and characteristics of both adjacent areas, often leading to high biodiversity.