Here's why:
* Fossil Record: The fossil record is a timeline of life on Earth. It shows that life has become increasingly complex over time.
* Geological Time: Earth's history is divided into eons, eras, periods, and epochs. The oldest rocks (and fossils) are found in the deepest layers. As you move up through the layers, you find younger and more complex fossils.
* Evolution: Evolution explains the gradual change and diversification of life on Earth. Simpler life forms evolve into more complex ones over time.
So, to answer your question, the most complex fossils are found in the youngest layers, which represent more recent geological periods.
However, it's important to remember:
* Fossil Discovery: Not all layers contain fossils, and not all fossils are equally well-preserved. Fossils are rare, and their discovery depends on various factors, including the environment where the organism died, the conditions of fossilization, and the geological processes that have affected the area.
* Evolutionary Trends: While the general trend shows increased complexity over time, there are exceptions. For example, some organisms have remained relatively unchanged for long periods.
