Changes in the natural environment occur over a wide range of time scales. Many systems are thus best considered to be in dynamic equilibrium – that is, they appear to be stable, but only over a certain duration of time. For example, Earth’s temperature over the last million or so years appears to be relatively constant. But since the Industrial Revolution of the 1850s – a relatively short timespan of 150 years – there has been a consistent rise in temperature. So it is important to realise that the time scale we adopt for the study of natural events can affect our understanding of them.
Nevertheless, despite some time scales being long in the past and appearing to be not so relevant today, they do have an influence in creating the world as we know it now. For example, Pangaea – the global supercontinent from Earth’s early age – fragmented about 140 million years ago, and the separated land masses began their long journey to become the continents as we know them today. The animals and plants that were on it had to then evolve on separate continents with different environments and climates, resulting in distinctly adapted species. An example of such evolution is that of marsupials like kangaroos, which are now uniquely found only in Australia. Another, more recent example is the evolution of the camel. (see Figure 13.)
The earliest known camel, called Protylopus, lived in North America (see 1 on the map in Figure 13) 40–50 million years ago. It migrated into South America, Asia (2) and then Africa (3), where it continued to evolve, resulting in the present day’s New World camelids such as llamas (South America), bactrian (Central Asia) and dromedary camels (Africa and Middle East).
After looking at all those patterns of biodiversity in time and space, you might be tempted to ask, what actually drives this variation and hence biodiversity? The answer(s) to this could be discussed by considering the drivers behind these developments. They could be environmental factors (e.g. climate), geological events (e.g. mountain building) or human activity (e.g. hunting or even climate change). These drivers are discussed in detail in the next section.