THE ORIGINS OF LIFE ON EARTH - evolution of species - The nature of fossils - How fossils provide evidence

http://www.bbc.co.uk/nature/history_of_the_earth Human civilization, in its most widely used definition, dates entirely within the Holocene. It’s this time period from when humans have had a significant impact on the Earth's climate and ecosystems to the present. Scroll down the page to see images of the geologic timeline Click on a few of the geological time periods (incl. The holocene) - Scrolling down the individual pages will tell you what species of animal lived during the time period and any other info Scroll further and mention the 5 big extinction events Cretaceous-Tertiary mass extinction - also known as the K/T extinction - is famed for the death of the dinosaurs. However, many other organisms perished at the end of the Cretaceous

The evolution of life http://www.wellcometreeoflife.org/ From David attenborough’s ‘tree of life series’ - There is an accompanying handout students can fill in if

EXTINCTION The permanent loss of all the members of a species from the face of the earth

Environmental changes The climate and environment on Earth is always changing These are the main causes of extinction, animals are not able to adapt quickly enough to the change in their environment

Evolution of the earth: ice ages http://www.bbc.co.uk/nature/history_of_the_earth/Cryogenian#p00cgy7m http://www.bbc.co.uk/nature/history_of_the_earth/Cryogenian#p00cgym0 Both videos discuss the snowball earth theory – the last ice age and its retreat

Again, the major eras, showing approx Again, the major eras, showing approx. where the 5 big extinctions occurred (including the one for the dinosaurs further discussed on the following slides) Cambrian is famed for its explosion of abundant and diverse life forms.

Hypothesis: Extinction of the dinosaurs 65 million years ago, a large meteor hit the earth The impact caused a large amount of debris to go into the atmosphere. This blocked the light and heat of the sun, causing the earth to cool: an ICE AGE There have been many different ideas put forward to explain why the dinosuars died out. The two most likely are that their habitat slowly changed, and that a meteor impact triggered their extinction. Gradualist theory The gradualist hypothesis points to declines in the numbers and diversity of different groups of land and marine animals. - extinction due to climate change. The climate at the end of the Cretaceous was cooling - and a fall in sea level reduced dinosaur and shallow water marine animal habitats. Impact theory - good geophysical evidence for the occurrence of an asteroid impact at the end of the Cretaceous. A band of clay rich in the mineral iridium was deposited at the end of the Cretaceous and has been found at many places in the world. This mineral is rare on Earth but more common in meteorites. It has been suggested that the impact would have triggered a nuclear winter scenario that would have caused the death of the dinosaurs as well as the pterosaurs, several families of birds and mammals and also marine animals such as the plesiosaurs and ammonites.

The Chicxulub crater in Mexico

Other causes of extinction predator: new predator comes to an area and wipes out a lesser species Disease: microorganisms can infect a species, killing it EX: Tazmanian Devil & cancer Competition: a mutation gives one species and advantage, causing the other to be unable to keep up

FOSSIL FORMATION There is no record of the origins of life on earth But, most scientists believe is was somewhere between 3 billion and 4.5 billion years ago!!

What is a fossil? The following slides show examples of fossils that scientists have found. Look carefully at each, and write down what you think they have in common.

Fossil One – Ammonite

Fossil Two - Turtle

Fossil Three – Sharks Teeth

Fossil Four – T. Rex

Fossil Five – Leaf

FOSSIL FORMATION We share the Earth with millions of different species of living organisms This is a tiny amount compared to the 4 billion species believed to have lived on Earth during its history

FOSSIL FORMATION Fossils are the remains of plants and animals from thousands or millions of years ago They are usually found in rocks

Fossils can be formed in different ways: CASTS OF ANIMALS OR PLANTS Formed when the hard parts of animals are replaced by minerals Human casts from Pompeii

2. IMPRESSIONS - These fossils are not actually animals or plants but traces they have left behind Ardley Quarry in Oxfordshire - Dinosaur tracks!?

3. ICE FOSSILS Some animals/plants do not decay after death but are preserved in ice http://www.youtube.com/watch?v=jl73TOqid0w&feature=related

http://www.youtube.com/watch?v=Zo49Pyhii-k&feature=fvwrel http://www.youtube.com/watch?v=jlwMYnoCGsM&feature=relmfu Fossil evidence of the earliest eukaryotes –in Australia ** mention what ‘snowball earth’ means as it’s mentioned in the video - Snowball Earth describes a theory that for millions of years the Earth was entirely smothered in ice, stretching from the poles to the tropics. it's now thought that there may have been more than one of these global glaciations. They varied in duration and extent but during a full-on snowball event, life could only cling on in ice-free refuges, or where sunlight managed to penetrate through the ice to allow photosynthesis. 2. Evolution of woolly mammoths – link to adaptions!