Fossil evidence

Question 1

What is a fossil?

Answer 1

Any preserved remains of a once-living organism. It provides a crucial piece of evidence and allows scientists to build a sequence of evolution for a particular organsim.

Question 2

What are the types of fossils?

Answer 2

1. Pretified fossils.
2. Molds and casts.
3. Carbon film.
4. Trace fossils.
5. Preserved remains.

Question 3

What is a petrified fossil?

Answer 3

Forms when minerals replace all or part of an organism.

Question 4

Describe how a petrified fossil is formed.

Answer 4

Water is full of dissolved minerals. It seeps through the layers of sediment to reach the dead organism. When the water evaporates, only the hardened minerals are left behind.

Question 5

Describe how a mould forms.

Answer 5

A mould forms when hard parts of an organism are buried in sediment, such as sand, silt, or clay. The hard parts completely dissolve overtime, leaving behind a hollow area with the organisms shape.

Question 6

Describe how a cast forms.

Answer 6

A cast forms as a result of a mould. Water with dissolved minerals and sediment fills the mould’s empty spaces. Minerals and sediment that are left behind in the mould make a cast. A cast is opposite of a mould.

Question 7

Describe how carbon film results in the formation of a fossil.

Answer 7

All living things contain an element called carbon. When an organism dies and is buried in sediment, the materials that make up the organism breakdown. Eventually, only carbon remains. The thin layer of carbon left behind can show an organisms delicate parts.

Question 8

What do trace fossils show?

Answer 8

The activities of organisms.

Question 9

Describe how a trace fossil forms.

Answer 9

An animal makes a footprint when it steps in sand or mud. Overtime the footprint is buried in layers of rock sediment. Then the sediment becomes solid rock.

Question 10

What are 3 ways fossils can be considered preserved remains?

Answer 10

1. Amber.
2. Tar.
3. Ice.

Question 11

Describe how an organism can be preserved in amber.

Answer 11

An organism such as an insect is trapped in a tree’s sticky resin and dies. More resin covers it, sealing the insect inside. It hardens into amber.

Question 12

Describe how an organism can be preserved in tar.

Answer 12

An organism such as a mammoth, is trapped ina tar pit and dies. The tar soaks into its bones and stops the bones from decaying.

Question 13

Describe how an organism can be preserved in ice.

Answer 13

An organism such as a woolly mammoth, dies in a very cold region. Its body is frozen in ice, which preserves the organism even its hair.

Question 14

What are 4 examples of materials that can bury organisms to create fossils?

Answer 14

1. Sand.
2. Mud.
3. Volcanic ash.
4. Other members of a species.

Question 15

What can slow down the decomposition process?

Answer 15

If buried rapidly or conditions are not ideal for decay then decomposition can be slowed.

Question 16

What are the 3 ideal conditions for fossilisation to occur?

Answer 16

1. Lack of wet and acidic soils.
2. Lack of oxygen in the soil.
3. Presence of alkaline soils.

Question 17

Describe why wet and acidic soils are not ideal for fossilisation.

Answer 17

Wet and acidic soils will dissolve the minerals in the bones and so no fossil is formed.

Question 18

Describe why a lack of oxygen in soil is ideal for fossilisation.

Answer 18

Soil with no oxygen like peat results in the complete preservation of soft tissue and bones. A lack of oxygen means there is no microorganisms decomposing the bone.

Question 19

Describe why the presence of alkaline soils is ideal for fossilisation.

Answer 19

Bones buried in alkaline soils produce the best fossils because the minerals in the bones are not dissolved. New minerals like lime and iron oxide are deposited in the pores of the bone, replacing organic matter. This causes the bone to be petrified.

Question 20

What are the 4 stages of fossilisation?

Answer 20

1. Death and decay.
2. Deposition.
3. Permineralisation.
4. Erosion/exposure.

Question 21

Describe the death and decay phase of fossilisation.

Answer 21

Soft body parts are decomposed or scavenged, leaving only the hard body remains.

Question 22

Describe the deposition phase of fossilisation.

Answer 22

The hard remains are rapidly covered with silt and sand, and overtime more layers continue to build.

Question 23

Describe the permineralisation phase of fossilisation.

Answer 23

Pressure from covering layers of dirt and rock cause the hard organic material to be replaced by minerals.

Question 24

Describe the erosion/exposure phase of fossilisation.

Answer 24

The movement of tectonic plates may displace the fossil and return it to the surface for discovery.

Question 25

How can fossils be uncovered or exposed?

Answer 25

• Erosion.
• Earth movements.
• Excavation sites.

Question 26

Outline the 6 steps of how a fossil is uncovered at an excavation site.

Answer 26

1. Section is marked out.
2. Small hand tools are used to remove soil.
3. Soil is sieved.
4. Photographs at each stage.
5. Each item is labelled and catalogued.
6. Fossils and artefacts are cleaned, pieced together and molds are made.