Fossils

Noadswood Science, 2012

Fossils

To understand how fossils are formed, and how they provide evidence about the past

Wednesday, May 3, 2023

Fossils

What are fossils?

As soon as plants and animals die they begin to rot away – however, sometimes the dead plants and animals can be turned into fossils (rock copies of the original plant or animal)

Fossils forms when dead plants or animals become covered in a layer of sediment which initially protects them…

Fossils

Most of the evidence for evolution comes from the fossil record

Fossils show how much, or how little, organisms have changed over time

One of the problems with the fossil record is that it contains gaps – not all organisms fossilise well, and there will be many fossils that have been destroyed by the movements of the Earth, or simply not yet been discovered…

Nautilus – a “living fossil”

Fossils

An organism dies, and settles on the sea floor Gradually it is covered with sediment which protects it, and

over time the layers build up As the layers build up the pressure increases, causing

sedimentary rock to form The dead organism undergoes a series of chemical changes

resulting in rock-like minerals taking the place of the original chemicals

Over millions of years the original organism is replaced with minerals, and a rock-like copy of the organism is left

Fossil Formation

Fossils can be formed in a couple of ways…

Some are stone copies of the organism, formed as the organism become petrified (turned to rock) by the deposition of minerals in the tissues as they decompose

Other fossils consist of impressions of the organism's shape, left behind in the surrounding stone as the tissues decompose

Most dead organisms decay very rapidly and their tissues are recycled, leaving no trace of their existence, but certain environmental conditions drastically slow down the decay process, thus helping to preserve the tissues, for example: - Insufficient oxygen (organism trapped in resin, e.g. amber) Low temperatures (organism frozen in glacier) High soil acidity (organism in peat bog)

Early Life

Why do you think most ‘early life’ has no fossil record?

There is a lack of evidence because scientists believe many early organisms were soft-bodied (soft tissue tends to decay away completely, making the fossil record incomplete)

Fossil Experiment

Produce your own fossil – initially make the impression by kneading the plasticine until it is soft, and press it flat so that it is ~2cm in depth

Place a shell / small bone in the petroleum jelly (so that it doesn’t stick) and push it into the plasticine – then carefully remove the shell / small bone (leaving only the impression)

To make the cast mix small quantities of the Plaster of Paris at a time with water in the container – pour this into the mould – when it is cold remove the cast (a replica of your original shell / small bone = a fossil)!

Fossil Experiment

Make mould Pour Plaster of Paris

Remove ‘fossil’

Dating

Where would we find the earliest fossils?

The earliest fossils are found in the deepest parts of the rock (over time more and more sediment is laid down, meaning organisms which dies the longest time ago are found in the deepest parts)

Evolution

How has our understanding of fossils over the past few hundred years led to a better understanding of evolution?

Most of the evidence for evolution comes from rocks and fossils – fossil remains have been found in rocks of all ages: - Fossils of the simplest organisms are found in the oldest rocks Fossils of more complex organisms are found in the newest rocks,

This supports the evolutionary theory that simple life forms gradually evolved into more complex ones, and that all animals have gradually evolved from a common ancestor

Evolution

Is it that simple?! What problems can you identify with fossil evidence being used solely as evidence for evolution?

Rocks move around, so you don't always find the newest rocks near the surface, or the oldest rocks deep down

Evolution is not always an orderly progression from simple to evermore complex organisms - it goes in fits and starts

Building up the story of evolution of any one species is difficult, as in most cases there are big gaps in fossil records (it can be like putting together a jigsaw puzzle with half the pieces missing)

Horse Evolution

One of the few animals for which we have a fairly complete evolutionary record is the horse because all the main stages of the evolution of the horse have been preserved in fossil form

Over 60 million years, the horse evolved from a dog-sized creature that lived in rainforests into an animal adapted to living on the plains and standing up to 2 metres high

Horse Evolution

In the process its multi-toed feet, that were adapted for walking across the forest floor, evolved into single-toed hooves more suited for running over open country

Human Evolution

Humans evolved from apes, however evidence for this transition is not abundant when we look to fossil records

The evolution from ape to modern man was by no means instantaneous, yet fossil evidence of how man gradually changed is still vastly incomplete – we are still in search of the ‘missing link’…

*Humans did not evolve from chimpanzees or any other modern ape – they are instead closely related organisms, probably all sharing a common ancestor

Human Evolution?

Time Line

Evolution states the different species on Earth have evolved from simple life forms which first developed more than three billion years ago (the Earth is about 4.5 billion years old)

The timeline below shows some of the key events in the evolution of life forms on Earth, from the first bacteria to the first modern humans…

Uncertainty

Why is there still uncertainty as to how life on Earth began?

Life forms could have come into existence in a primordial swamp / maybe simple organic molecules were brought to Earth on comets which then became more complex

These hypothesis cannot be supported or disproved because there is a lack of valid and reliable evidence – explain what this means…

Valid & Reliable

Valid means that the data is reliable and answers the original question – this data simply isn’t available for early life

Reliable means that the data can be repeated and reproduced by others – the early conditions of the Earth are not categorically known, and life (to this point) has not been artificially created (so you have no repeatable data)