Here's a breakdown:

* Becquerel's discovery: Becquerel was studying the fluorescence of uranium salts when he accidentally discovered that these salts emitted a type of radiation that could penetrate opaque materials. He initially thought this radiation was related to fluorescence, but further experiments revealed it was a new phenomenon.

* Marie and Pierre Curie: Becquerel's work inspired Marie and Pierre Curie to investigate further, leading to the discovery of other radioactive elements like polonium and radium.

* Importance: The discovery of natural radioactivity revolutionized our understanding of the atom and the nature of matter. It led to the development of nuclear physics, nuclear medicine, and eventually, nuclear power.

While Becquerel is credited with the initial discovery, the Curies played a crucial role in furthering our understanding and exploring this fascinating phenomenon.