The Cambrian Explosion, according to the Encyclopedia Brittanica, is the unparalleled emergence of organisms during what secular scientists call the Cambrian period.
This event is characterized by the sudden appearance of many of the major phyla and animal groups in the fossil record.
There are many other puzzling issues like this, such as fossils intersecting multiple layers of strata that are supposed to be millions of years old each, or why some fossils, older ones supposed to have evolved after other newer fossils did, have been found above the newer fossils in some instances (older fossils should be below newer ones), etc.
The problem is, two people with completely different points of view, can look at the exact same data, and come up with completely different conclusions. The data is the same. How is this possible?
Let me give you a good example.
We know that God created Adam and Eve on Day 6 of the Creation, according to the Bible in Genesis. And that they were created as adults.
If a Christian and a secular scientist were to examine the pair, on that very day after they were created, they would come to completely different conclusions.
The secular scientist for example, would examine them and determine they were decades old. The Christian would know they were only a day old. They both have the same data. But vastly different conclusions.