1. Earth’s Past

2. Fossils are traces or remnants of past life
Fossils are traces or remnants of past life. Many fossils are found in rock. Rocks, fossils, and other natural evidence provide information about how Earth and life on Earth have changed over time.

5. original remains
A fossil that is the actual body or body parts of an organism. There are 3 different substances original remains are found are the following:
1. Ice- Ice preserves remains (Mammoth)
2. Amber- Resin from tree hardened and preserves remains (insects)
3.Tar- Pools of tar preserve remains (Saber- toothed cats)

10. Fossils in Rocks
These fossils are impressions or traces made of rock and provide indirect evidence that the organisms were there.
There are 4 types of fossils in rocks:
Mold and Cast
Petrified wood
Carbon Films
Trace fossils

11. Process and Example of Mold and Cast
1. Organism dies and falls into soft sediment.
2. Over time, the sediment becomes rock and the organism decays, leaving a mold.
3. Minerals fill the mold and make a cast of the organism.
Example- Clams, snails

12. A mold and cast fossil is formed when minerals take the shape of a decayed organism.

13. Mold and Cast Fossil

14. Petrified Wood The stone fossil of a tree is called petrified wood.
Process - A fallen tree can be covered with sediment. Over time, water passes through the sediments and into the trees cells. Minerals that are carried in the water take the place of the cells, producing a stone likeness of the tree.
Example- petrified forest

15. Petrified Wood

16. Carbon Films Carbon is an element that is found in everything living.
Process- Sometimes when dead plant or animal decays, its carbon is left behind on a visible layer.
Example- moth 10 million years old

17. Carbon Film

18. Trace Fossils
Trace fossil is a fossil that demonstrates that a particular living organism existed.
Process of how the trace fossils are preserved is when weather changes drastically and causes weathering and erosion to occur which preserves events that occurred prior to the change.
Example of Trace fossils include preserved footprints, trails, animal holes, and even feces.

19. Trace Fossils

20. Scientists combine information about the relative and absolute ages of rocks and fossils to construct a timeline of Earth.

21. The age of an event or object in relation to other events or objects
relative age
The age of an event or object in relation to other events or objects
(sedimentary rock only)

22. absolute age
The actual age in years of an event or object. (igneous rock- radioactive dating and once living organisms-carbon dating).

23. index fossil
A fossil of an organism that was common, lived in many areas, and existed only during a certain span of time. Index fossils are used to help determine the age of rock layers.

24. half-life
The length of time it takes for half of the atoms in a sample of a radioactive element to decay into atoms of another element

29. Sedimentary rock layers show the order in which rocks formed
Sedimentary rock layers show the order in which rocks formed. The order of the layers is used to determine the relative ages of fossils found in the rock.
Radioactive dating can be used to determine the absolute age of igneous rock.