Back when the Earth was crawling with trilobites ... the Ordovician period—which ran between 485.4 million years and 443.8 million years ago—including the positions of 21 impact craters ...

Researchers have proposed that Earth may have had a ring system 466 million years ago, during a period of intense meteorite bombardment known as the Ordovician impact spike. This finding ...

The Earth was already more than 600 million years old when life began ... which show up in the fossil record as early as 3.4 billion years ago. As their numbers multiplied and supplies of their ...