What Are Fossils?

Fossils are the preserved remains or traces of ancient organisms found in rocks.
They provide evidence of how life on Earth has changed over time.

💡 Key Concept: Fossils help scientists understand evolution, extinction, and past environments.

How Are Fossils Formed?

There are three main ways fossils can form:

1️ From Hard Parts

✔ Bones, teeth, shells don’t decay easily and are replaced by minerals over time
✔ This creates a rock-like copy of the original structure

2️ From Casts and Impressions

✔ Organism decays in mud, leaving an impression (e.g. footprints, burrows)
✔ The space fills with minerals – forming a cast fossil

3️ From Preservation

✔ Some organisms are trapped where decay doesn’t occur (e.g. ice, amber, peat bogs)
✔ This preserves soft tissues, hair, or whole bodies

Why Don’t We Have Fossils of Every Organism?

❌ Many early organisms were soft-bodied – no hard parts to fossilise
❌ Fossils can be destroyed by geological activity (e.g. earthquakes)
❌ Conditions needed for fossilisation are rare

What Do Fossils Tell Us?

✔ How species have evolved over time
✔ How organisms have adapted to changing environments
✔ Evidence of extinction events
✔ Clues about ecosystems from millions of years ago

💡 Fossils support Darwin’s theory of evolution by natural selection.

The Fossil Record and Gaps

• The fossil record is incomplete
• There are gaps due to missing fossils, decay, or lack of discovery
• But enough fossils exist to show clear patterns of change over time