There isn't a large gap of time between the evolution of algae and trilobites. In fact, they both existed during the same period, the Cambrian Explosion, which took place about 541 million years ago.

Here's a breakdown:

* Algae: Algae evolved long before the Cambrian Explosion, likely billions of years ago. They are among the earliest forms of life on Earth and were crucial in oxygenating the atmosphere.

* Trilobites: These marine arthropods first appeared in the early Cambrian period, roughly 521 million years ago. The Cambrian Explosion is known for its rapid diversification of life forms, including trilobites.

So, while algae predate trilobites by a significant amount, they were both thriving during the Cambrian period.

It's important to note that the fossil record isn't perfect, and there are gaps in our knowledge of the evolution of life. We are constantly discovering new fossils and refining our understanding of evolutionary history.