1. Where’s the Proof? Actually, the evidence is in the rocks!
Each of these rock layers represents a period of time in Earth's history, so the entire sequence of layers is another timeline.

2. Layers and Layers!
All over the world, rock layers are deposited on top of layers that were already there.
As more and more layers are deposited, the older rock layers end up at the bottom of the sequence and the newer ones toward the top.
In geology, this is referred to as the Law of Superposition.

3. Fossils can indicate time too
So the law of superposition gives us the relative age of the fossils.
7. The Law of Superposition: in any undisturbed sequence of rocks deposited in layers, the youngest layer is on top and the oldest on bottom, each layer being younger than the one beneath it and older than the one above it.

4. What is a fossil?
Simply put, a fossil is the remains or evidence of any creature or plant that once lived on the Earth.

5. 2 Types of Fossils
8. Type I -the remains of the dead animal or plant or the imprint left from the remains.
Type I includes:
bones
teeth
skin impressions
hair
the hardened shell of an ancient invertebrate (an animal without a backbone) like a trilobite or an ammonite, or the
impression of an animal or plant, even if the actual parts are missing.

6. 2 Types of Fossils
9. Trace (Type II) - Something that was made by the animal while it was living that has hardened into stone. These are called trace fossils.
Trace (Type II) includes:
footprints
burrows
coprolite or animal poop

7. How Do they Become Fossils?
Type I fossils can be the actual thing that it once was, like a piece of bone or hair or feather. More often the bone material is replaced by different minerals contained in the liquid of the sediments that buried it. What was once bone is now some sort of crystal.
This process also takes place with shells, exoskeletons and wood.

8. Permineralization
10. Permineralization is when the original parts of fossils (bones and such) are replaced with sediments.
Key word to remember here is mineral.

9. Another way…
Another way that fossils are preserved is by petrification.
11. In petrification, every detail down to the cellular level is duplicated in the minerals.

10. Molds Vs. Casts
Type I can also be molds or casts of the original animal or plant part.
12. Mold - If the original organism decays, leaving an imprint and an empty space, it is called an exterior mold or simply a mold.
13. Cast - If a space in the structure is filled with minerals and then the original animal or plant part dissolves, it is called a cast.

11. This kind: Radiometric Dating
Rocks are made up of many individual crystals, and each crystal is usually made up of at least several different chemical elements such as iron, magnesium, silicon, etc.
Most of the elements in nature are stable and do not change.
However, some elements are not completely stable in their natural state