A layer of tissue that surrounds the body of mollusks and some other animals, or the layer of the Earth beneath the crust.

Relating to the sea or ocean, often used to describe organisms living in or adapted to life in salty water.

A group of mammals characterized by giving birth to underdeveloped young, which are carried and nursed in a pouch.

A pouch-like structure in female marsupials, used to carry and nurse their young.

A measure of the amount of matter in an object, often expressed in kilograms or grams.

Events in Earth’s history when large numbers of species went extinct over a relatively short period of time.

The total number of protons and neutrons in the nucleus of an atom.

A form of artificial selection where individuals with the most desirable traits are selected to reproduce.

An analytical instrument used to measure the mass-to-charge ratio of ions, used in chemistry and biology for identifying and quantifying substances.

The branch of medicine that deals with the study of the breast, its diseases, and treatments.