fossils

What are fossils

Either a complete organism or the remains, imprints or traces of an organism

Where are most fossils found and how is this rock made

Sedimentary rocks, when clay and sand particles are carried from one place to another by water or wind and hardens over many many years

What are the ideal conditions for fossilisation

1. Organism must be buried immediately after it dies. This creates anaerobic conditions which allows the functioning or decomposers.

2. Harder parts (bones, endoskeleton, teeth, hair, etc) will simplify fossilisation. Soft tissue rarely preserves, exceptions like insects in amber as well as mammoths in Ice.

Explain the formation of fossils in sedimentary rocks

1. Organisms die and are quickly buried (on land or in bottom of seas or dams)

2. Lack of O2 slows down decomposition, soft tissue decays with help of bacteria and hard parts remain intact

3. Increasing layers make sure Body is covered and buried in sediment and compressed to form sedimentary rocks

4. Rocks are pushed to surface as a result of the movement of earth over many centuries, fossils are exposed by the erosion or human activity

5. The organic parts of bones and teeth decay and are replaced with minerals. The fossil is formed

What are the different fossil types

Body fossil

Mould fossil

Cast fossil

Trace fossil

What are body fossils

They can be complete organisms or part of an organism

A organism that can be reserved in ice, amber anaerobic swaps, etc

What are mould fossils

The hard parts of an organism are trapped in sediment. The hard parts decomposes and leaves imprint or mould

What are cast fossils

When mould is filled with minerals and fossilise to form replica.

What are trace fossils

Marks of an organism that once lived. Evidence of an organism’s activity

How can the age of fossils be determined

Using relative dating or radiometric dating

What is relative dating

Archaeologists study the sedimentary layers above and below a fossil to determine the age of the fossils relative to another fossil or geological event.

Older fossils occur in sedimentary layers below the fossil and more recent species in the layers above the fossil

Not very accurate

What is radiometric dating

Based on radioactivity

Carbon is the most common form of radioactive isotopes and potassium and uranium

The more the radioactive element in a fossil has decayed, the older the fossil

The rate of decay of a radioactive isotope is known as half-life. It is the amount of time it takes to break down half of the mass of the radioactive material

What is a direct method

Used with fossils younger than 50 000 years

Age is determined by carbon dating

What is a indirect method

Used with fossils older than 50 000 Years

Determine the age of the rocks that the fossil is found in using isotopes decay

The age of the rock= the age of the fossil

What are transition fossils

As intermediate or in-between forms that link distinct groups

What happened in the Cambrian period

Explosion, first vertebrates

What happened in the Precambrian period

First invertebrates, origin of eukaryotes

What happened in the Devonian period

First amphibians and insects

Mass extinction

What happened in the Permian period

Increase in reptiles and decrease in amphibian

Mass extinction

What happened in the Triassic period

First dinosaurs

First mammals

Mass extinction

What happened in the Jurassic period

First birds

Dinosaurs

What happened in the Cretaceous period

Extinction of dinosaurs

Mass extinction

When were the 5 mass extinctions

Ordovician

Devonian

Permian

Triassic

Cretaceous

What are the bird and reptile characteristic of a Archaeopteryx

Reptile- sharp teeth in sockets, fingers with claws, strong long limbs, long bony tail

Bird- feathers, wishbone, foot with 3 toes, hollow bones

What appeared in the Cambrian explosion

Early forms of all animal groups

Why is it called the Cambrian explosion

Relatively short time in which a huge diversity of life forms appeared

What is the reasoning of the appearance of many species in the Cambrian explosion

Development of hard body parts that fossilise easier or rapid speciation

What is a mass extinction

When many species disappear over the same period of geological time

What are the 2 particularly significant mass extinctions

End of the Permian period- extinction of 96% of all life

End of Cretaceous period- extinction of dinosaurs

What are the 5 mass extinctions and their causes

End of Ordovician period- climatic change (possible ice age)

Late Devonian period- possible ice age with drop in sea levels

End of Permian period- climatic change (biggest mass extinction in geological history)

End of Triassic period- uncertain (possible ice age, volcanic eruption or global warming)

End of Cretaceous period- possible meteorite collision with earth or volcanic eruptions

What caused the mass extinction in the end of the Ordovician period

Climatic changes- possible Ice age with drop in sea level (algae dominate)

What caused the mass extinction in The late Devonian period

Possible ice age with drop of sea level (first amphibians and and insects)

What caused the mass extinction in The end of the Permian period

Climatic change possible ice age, volcanic eruptions (96% of all life on earth wiped out)

Increase in reptiles and decrease in amphibians

What caused the mass extinction in The Triassic period

Uncertain (possible ice age, volcanic eruption, global warming)

First dinosaurs and mammals

What caused the mass extinction in The ems of the Cretaceous period

Possible meteorite collision with earth or volcanic eruption