Life in the Past
Since the discovery of fossils, we now know that lots ofdifferent species lived long ago in the past. Most of them havedied out, or become extinct. Many of these plants and animalswere completely different from things alive today – such asdinosaurs and giant woolly mammoths.
Charles Darwin wanted to know why there were so manydifferent species present on Earth. He noticed that things thatlived a long time ago differed from those alive in his time,but often looked a bit like modern animals and plants.He wondered whether, over time, living things could graduallychange, or evolve, into new forms. So each species wouldhave arisen from one that came before it – like dogs haveevolved from wolves.
Part of the evidence for this idea comes from the fossil record– the presence of fossils in rocks of particular ages. We nowknow that the Earth is many millions of years old. Its history isdivided up into different periods such as the Jurassic. Eachperiod has its own typical types of fossil – a record capturedin stone of the things that were alive at the time.
Objective
You are going to make a ‘timeline’showing how life on Earth has changedover the past 4.6 billion years. First ofall you will assemble the timeline fromall its different era’s. Then you willwork out when particular types ofanimals first appeared.You will also see when two ‘massextinctions’ killed off many species,including the dinosaurs.
Activity
1 Carefully cut out the differentgeological era’s, making sure youdo not cut off the tabs.
2 Arrange the eras in order of oldest to youngest. The tabs
are the age of the Earth in millions of years. Glue them together.
3 Cut out the different animals.
4 Glue the animals onto the timeline when they first appeared.The numbers on the tabs show when they first appeared, in millions of years.
5 Lastly cut out the two Mass Extinctions and glue them onto your timeline
Questions-Open your text book to Ch 12.5 (pg. 376).
1)How soon after the Earth was formed did the 1st living things (bacteria) appear?
2)How long were bacteria the only living things on Earth?
3)Circle which group came first in each of the 3 lines below.
- Fish or Mammals
- Dinosaurs or Birds
- Sea creatures or animal that live on land
4)On the timeline you just created, label "Cambrian explosion" where it belongs.
Define what the Cambrian explosion was.(pg. 376).
5)The paleozoic era was a time of major change producing many species living in the shallow seas. At the end of the Paleozoic era the shallow seas disappeared when the continents merged forming Pangea. Write Pangea on your timeline where it belongs. How could this have caused the mass extinction at the end of the Paleozoic era?
6)The Mesozoic erawas the time of the dinosaurs. What caused the extinction of the dinosaurs? (pg. 377).
In the geologic timescale below, notice how speciation occurs after a mass extinction event. That is, new species evolve to fill the habitatsleft behind by the species killed in the mass extinction. Mass extinction events are identified by sudden decreases in biodiversity.
7)Use the diagram above. With the extinction of the dinosaurs, what animals increased their biodiversity in the Cenozoic era?
8)Circle on the diagram at the top of the page wherespeciation is occurring. And explain what it is.
9)Why are episodes of speciation most dramatic after mass
extinctions or even after the appearance of novel
characteristics such as feathers and wings?
10)Looking at the diagram to the right, which group of
species had the greatest biodiversity in the Triassic period?