The diagram below represents a simplified geological time-scale showing how the number of families (groups of related species) has changed over a period of time.

Here are the answers to the questions based on the provided diagram:

QUESTION 3.2

3.2.1 How many mass extinctions took place since the creation of the earth?
Based on the provided diagram, which covers the last 600 million years, there are $\boxed{\text{5 mass extinctions}}$ shown (Ordovician, Devonian, Permian, Triassic, Cretaceous).

3.2.2 Which mass extinction took place towards the end of the Palaeozoic era?
The mass extinction that took place towards the end of the Palaeozoic era was the $\boxed{\text{Permian extinction}}$.

3.2.3 Which era had the longest duration?
The $\boxed{\text{Palaeozoic era}}$ had the longest duration, lasting approximately from 540 million years ago to 250 million years ago (about 290 million years).

3.2.4 Name TWO factors or events known to have caused mass extinctions.

• $\boxed{\text{Asteroid impacts}}$
• $\boxed{\text{Massive volcanic eruptions}}$ (Other valid answers include significant climate change, sea-level changes, or ocean anoxia).

3.2.5 When did the Triassic extinction take place?
The Triassic extinction took place approximately $\boxed{\text{200 million years ago}}$.

3.2.6 Which extinction was the biggest in terms of the number of families that went extinct?
The $\boxed{\text{Permian extinction}}$ was the biggest in terms of the number of families that went extinct, with approximately 300 families dying out (from ~400 to ~100). The Cretaceous extinction also shows a drop of about 300 families (from ~600 to ~300).

3.2.7 Scientists believe that we are currently experiencing the sixth mass extinction. What is thought to be the cause of this mass extinction?
The current (sixth) mass extinction is primarily thought to be caused by $\boxed{\text{human activities}}$, including habitat destruction, climate change, pollution, overexploitation of resources, and the introduction of invasive species.