The article focuses on the keyword “What happened 400 million years ago,” specifically highlighting the Devonian Period, which occurred around 400 million years ago. The search intent it addresses is educational, targeting readers interested in paleontology, geology, and the history of life on Earth.

The content offers detailed information about the significant events of the Devonian Period, emphasizing the diversification of fish species and the broader ecological and geological changes that took place during this time. It aims to provide a comprehensive understanding of this pivotal era in Earth’s history, making it suitable for webmasters looking to enhance their site’s educational resources or attract an audience interested in natural history.