In our last #FossilFriday post, the Horniman’s Deputy Keeper of Natural History Paolo took a look at some of the scientific principles used to understand the age of the Earth and the life of the past. This time he takes a look at how fossils have helped our understanding of how life has changed over time.
Once geologists were able to work out the relative age of different rock types they divided them into geological Periods, with names reflecting something characteristic about them. Perhaps it’s unsurprising that the first to be recognised was the Carboniferous – named because of the economically important carbon-rich coal seams found in beds of that age.
But names could also be a reference to where rocks of the type were found: the Devonian is named after Devon. Or they could be a reference to the ancient tribes that lived in those regions: the Ordovician is named after the Celtic tribe of the Ordovices.
You can see examples of British fossils from each of the geological Periods in the cases around the balcony in the Natural History Gallery – each with a map showing where rocks of that age are found.
As more geological Periods were named, they were grouped together into Eras based on the types of organisms preserved as fossils. The oldest rocks with fossils were dominated by the remains of small and quite simple animals, many of which were unlike those alive today. These rocks were placed in an Era called the Palæozoic – the Era of 'Ancient Life'.
Younger rocks that were missing some of the major fossils found in the Palæozoic Era, but which still contained fossils of animals quite different to those seen today, were placed in the Mesozoic – the Era of 'Middle Life'.
Even younger rocks that only contained fossils of animals of a type similar to those found today were grouped into the Cænozoic – the Era of 'New Life'.
In the early 19th Century the different types of life that were seen through time were considered to be links in a 'Great Chain of Being', but how that chain was formed was a mystery. One scientist who tried to explain this chain using natural laws, rather than by assuming the input of a creator, was Jean-Baptiste Lamarck.
In 1800 Lamarck suggested that there was a complexifying force (a natural tendency for biological organisms to become more complex due to internal factors) and an adaptive force (use or disuse of characteristics would lead an organism to adapt to its environment).
Lamarck also suggested that animals could pass on the characteristics that they acquired in life to their offspring - for example, by stretching to reach high leaves, he suggested that Giraffes would lengthen their neck and this change would be passed on to the next generation. This theory became known as Lamarckism.
This idea led to the introduction of the term 'Evolution' as we think of it today. Lamarck’s idea didn’t account for what was observed in nature very well, but he did help set the stage for later scientists who proposed new ideas about evolution, including Alfred Russel Wallace and Charles Darwin.
I’ll say more about their contribution and how Evolution is displayed at the Horniman in my next post.