U4 AOS2 Topic 7: Fossil Record

Fossil records

Fossil record is the information we get from fossils, it is arranged in chronological order, and it helps us to study the history of life on earth.

Cambrian explosion

It was a period 535 million years ago and was the time when there was a rapid increase in the diversity of multicellular life, and it was characterized by hardened body parts that we see today such as shells or bones.

All living things on earth originated from a single celled prokaryote that existed around 3.8 billion years ago, this prokaryote had offspring with the ability to photosynthesise; this oxygenated the atmosphere allowing eukaryotes to survive which eventually led to Cambrian explosion.

Extinction is the end of a species on a global or regional level and the most common example of this is the extinction of dinosaurs around 65 million years ago.

Fossil is the preserved body of a dead organism and the process by which these fossils form is known as fossilisation, and the process of fossilisation occurs when  the organism is not exposed to oxygen, which means it should be covered by a sediment (tiny pieces of naturally occurring solids such as earth and rock that settle at the bottom of a liquid),  overtime sediment layers build upon each other in a compact way forming a sedimentary rock, and within this rock the fossilised  remains can take various forms such as mould or cast fossil.

Mould fossil fossil formed when a living thing decomposes underneath sediment, creating a cavity in the shape of the dead organism.

 Cast fossil formed when a mould fossil is filled with sediment.

Trace fossils fossil or structure that indicates the presence of organism instead of the organisms themselves.

There are a few conditions that increase the likelihood of fossilisation, such as

Physical protection from decomposers: like bacteria, cool temperatures, low oxygen availability and low light exposure.

Relative dating it is used to determine the age of a fossil by comparing it to the other fossils present in the surrounding area.

Absolute dating is used to determine the absolute age of a fossil by measuring their amounts of radioisotopes.

Fossil Succession: This principle states that fossils found in the same sedimentary rock layer are of the same age, and fossils in a higher or a lower sedimentary layer will be older or younger.

Relative age: the age of a fossil as determined by relative dating techniques.

Researchers only need to know the age of the rock layer where the fossil was found, each layer of a sedimentary rock represent a specific period, and we call it as the geological timescale. 

Index fossils are fossils of organisms that were widespread and lived for a short period of time, we can use them to determine the age of the fossils that are found in the same rock layer. For the best index fossils, the species must be, physically distinctive, have had a large population, have existed in many geographical areas, and only lived within a known short period of time.

Transitional fossil: a fossil that shows traits that are common to both its ancestral group and its descendant group.

Half-life: the time taken for half the mass of a radioisotope sample to break down into its products.

Radioisotopes are unstable elements and overtime they will break down into a more stable product such as carbon 14 will change to nitrogen 14.

Dating period the range of time since fossilisation in which a particular radioisotope series can be used, after this time has passed most of the radioisotope will have broken down into their products, making it a challenge to determine the age of a fossil.

 

Radiocarbon Dating: This is a method used to find out the age of a fossil by measuring the amount of radiocarbon, a type of radioactive carbon.

All the living organisms contain carbon, which exists in two forms Carbon 12C and Carbon 14C, while the organism is alive the ratio of the 12C to 14C matches with the atmosphere, and after an organism dies its carbon 14C starts to decay into nitrogen N14, so the 14C decreases overtime after death but the 12C remains unchanged. Researchers measure the remaining amount of 14C in an organism and they match it with the normal 12c to 14c ration in the atmosphere, this can help to determine the age of the fossil.