Fossils

D. Crowley, 2008

Fossils

To know how fossils are formed

Sedimentary

Complete the sedimentary rocks worksheet

Sedimentary

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

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)

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)

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?