Science 7 Unit E : Planet Earth

Topic 8 - Fossils

Trilobites are one of the most famous ___________________. They date from a time before

the dinosaurs, about _________________________. Trilobites lived in

warm ocean water and __________________.

Types of Fossils

Petrified FossilIf a carcass is in water and sinks to the bottom, the body can be buried by sediment. Soft parts, such as skin, muscle, or organs decay rapidly and are rarely found as fossils. The hard parts (bones, shells, or teeth) may be altered to become fossilized remains. When water penetrates the bones of a dead animal, the water dissolves the calcium carbonate in the bones. A deposit of another very hard mineral, silica (quartz) remains, turning the bones into a

_____________________________________.

Carbonaceous Film FossilWhen an organism is buried under many layers of sediment, pressure and heat may build up, leaving a thin film of carbon residue on rock surfaces. The residue forms an outline of the organism. The outline is called a

_____________________________________.

Original Remains FossilSometimes the actual organism or part of it may be preserved as a fossil. These are called

_________________________.

Trace Fossil ____________________are evidence of an animal activity. Worm holes, burrows, and footprints can be fossilized. They provide a fascinating glimpse of

_________________.

Science 7 Unit E : Planet Earth

Fossil Mould and Cast FormationSometimes an organism falls into soft sediment, like mud. As more sediment falls, the original sediment gradually turns into rock. Water and air pass through pores in the rock, reaching the organism. Its hard parts dissolve, leaving a cavity in the rock

____________________________________.

Other sediments or minerals may fill the hole, hardening into rock and producing a

____________________________________________.

Science 7 Unit E : Planet Earth

Topic 8 Review

1. What type of clues can fossils provide about Earth's history?

2. What conditions are necessary for fossils to form?

3. Name five types of fossils and describe how each is formed.

Petrified –

Carbonaceous film –

Original remains –

Trace fossils –

Mould fossil –