Earth’s Past Earth’s Past

FossilsFossils are traces or remnants of past are traces or remnants of past life. Many fossils are found in rock. life. Many fossils are found in rock.

Rocks, fossils, and other natural Rocks, fossils, and other natural evidence provide information about evidence provide information about how Earth and life on Earth have how Earth and life on Earth have

changed over timechanged over time. .

original remainsoriginal 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. 1. Ice- Ice preserves remains (Mammoth)

2. 2. Amber- Resin from tree hardened and preserves remains (insects)

3. 3.Tar- Pools of tar preserve remains (Saber-toothed cats)

Fossils in RocksFossils 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:

1. Mold and Cast

2. Petrified wood

3. Carbon Films

4. Trace fossils

Process and Example of Mold and Process and Example of Mold and CastCast

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

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

Mold and Cast FossilMold and Cast Fossil

Petrified WoodPetrified 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

Petrified Wood Petrified Wood

Carbon FilmsCarbon 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

Carbon FilmCarbon Film

Trace FossilsTrace 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.

Trace FossilsTrace Fossils

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

relative agerelative age

The age of an event or object in relation to other events or objects

(sedimentary rock only)

absolute ageabsolute age

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

index fossilindex 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.

half-lifehalf-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

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.