Fossils

What is a fossil?

• A fossil is the preserved remains or traces of ancient organisms.

• They are found in rocks and provide evidence of life from millions of years ago.

Why do scientists study fossils?

✅ Evidence for evolution – Show how species have changed over time.
✅ Reconstruct ancient environments – Reveal past climates and ecosystems.
✅ Track extinction events – Help understand mass extinctions.

What are the three ways fossils can form?

1⃣ Mineral Replacement (Hard Parts Fossils) – Bones, shells, and teeth are replaced by minerals, turning them into rock-like structures.

2⃣ Casts and Impressions – Organisms leave behind moulds or imprints in soft material, which hardens over time.
3⃣ Preservation in Special Conditions – Some organisms are trapped in amber, ice, or peat bogs, preventing decay.

How does mineral replacement create fossils?

1⃣ Organism dies and is buried quickly by sediment (e.g., sand, mud).
2⃣ Soft tissues decay, leaving only hard parts (bones, teeth).
3⃣ Water rich in minerals seeps in, gradually replacing organic material with minerals.
4⃣ Over millions of years, the fossil forms inside rock layers.

How do cast and impression fossils form?

• Casts – If an organism dissolves but leaves a hollow shape, minerals fill it and form a solid copy.

• Impressions – Footprints, leaves, or shells press into soft mud, which later hardens into rock.

What conditions prevent decay and preserve fossils?

❄ Ice/Permafrost – Freezing temperatures prevent bacteria from decomposing the body.
💦 Peat Bogs – Lack of oxygen stops microbes from breaking down the body.

What is the fossil record, and why is it important?

• The fossil record is the collection of all known fossils.

• It helps scientists understand how life evolved and identify extinct species.

Why are there gaps in the fossil record?

❌ Not all organisms fossilize – Soft-bodied organisms decompose before they fossilize.
❌ Fossils can be destroyed – By earthquakes, erosion, or volcanic activity. ( geological activity)
❌ Fossils are difficult to find – Some remain undiscovered deep underground.

How do fossils provide evidence of extinction events?

• Fossils show species that no longer exist (e.g., dinosaurs).

• Large gaps in the fossil record indicate mass extinctions (e.g., asteroid impact 65 million years ago).

What evidence do fossils provide for evolution?

✅ Fossils show gradual changes – Transitional fossils link ancient species to modern ones.
✅ Common ancestors – Similarities in fossils suggest all species share a common ancestor.
✅ Extinct species – Fossils reveal species that have disappeared due to natural selection.