Silurian
The Silurian was the first period that produced fossils on land that are macroscopic. That means you can see them without using a microscope. These fossils are moss forests along lakes and streams, and millipedes and scorpions on land later in the period. The fossil record of Eurypterids (sea scorpions) reached its greatest extent in the middle Silurian, about 430 million years ago.