Thank you very much to everyone who submitted an entry to Competition 1: The fossil record! Below you can read some of the winning entries, as selected by our team of markers.
1st place (Year 10): Vienna D. & Eleanor G.
Vienna’s winning entry
Palaeontologists estimate that only around 1% of all animals to have ever lived have been found as fossils, this is because fossilisation is so rare, due to the many factors necessary for fossilisation to occur.
Firstly, the animal itself must fit certain criteria in order to become a fossil in the future. The organism must have solid body parts made up of bone, for example a skeleton, teeth or a shell. For instance, it is unlikely a jellyfish will undergo fossilisation as it is made up mostly of soft flesh. Therefore, very little is known about the evolution of the jellyfish and its origin. This is because once the organism is dead it must avoid being destroyed either by decomposition or erosion, and bone is less likely to be decomposed and is more resistant to erosion. However, even if the organism manages to avoid being destroyed, it must then undergo a rapid burial to avoid being affected by further biological (being eaten or moved by other animals) or environmental (weathering or erosion) factors. Finally the organism must remain undisturbed for many years to allow for fossilisation.
Another factor that influences fossilisation is the environment. For example rainforests don’t create many fossils as they are hot and moist meaning dead matter is decomposed more quickly and therefore doesn’t have enough time to be buried. Likewise, a Rocky Mountain top is also not suited to fossilisation due to a lack of fine sediment. The best place is most likely at the bottom of the ocean or a lake, because it allows the organism to be buried quickly with lots of sediment.
Now I am going to look at how scientists came up with the idea that only 1% of all animals to have ever lived have been found as fossils. Firstly extinction can be observed. It is estimated that somewhere between 40 000 and 500 species are lost every year, and although this seems a great span of possibility, when just looking at fossil data alone it is suggested that only 5 species are lost each year. Consequently, fossil data only represents 1% (at the most) of current extinction. As 99% of species are extinct a huge number of fossils would need to be available to prove every species existence with fossil evidence, so it is therefore viable that only a small percentage of all species are represented with fossil data.
In conclusion, fossilisation is unlikely in many situations, so therefore doesn’t happen often, meaning fossil data only represents a small percentage of animals to have existed. Scientists know this by looking at the amount of extinctions to occur in a certain period of time and how this quantity compares to the number of extinctions supported with fossil evidence.
Eleanor’s winning entry
If an organism becomes a fossil, some of it remains after it dies. But, in most cases, it would rot away, be eaten or be scattered and eroded by wind, rain or tide. Over millennia, if it is not protected, it will just become dust by erosion. What does remain will usually be the hard parts, which could slowly become buried in rock sediments. This is rare and could only happen in certain places like riverbeds or ocean bottoms. Over time, as the layers of sediment build up, they compact and turn to rock. The remains slowly dissolve in the water seeping through the rock and minerals replace the remains of the organism. This makes a rock copy of the specimen, which is a fossil.
Only a very tiny percentage of existing fossils could have been found. It is estimated that sedimentary rocks, where fossils will be, cover nearly three quarters of the earth’s surface and fossils have been found well over one mile under the surface. For example, a 200-million-year-old dinosaur specimen was found 1.4 miles below the bottom of the North Sea by an offshore oil drilling platform.
This shows that the likelihood of an animal ever forming a fossil is very low and, if it does, then the chance of it being found is also extremely low.
The number of species found in fossils has been estimated to be less than 5% of the number of the species living now. We can use this to guess the percentage of the number of fossil species found compared to the number of species that has ever lived. It is likely to be much less than 5%. This is because:
- The number of living species is far less than the number of species that has ever lived as five mass extinctions have been identified and each lost at least three quarters of all the species that were alive then.
- The estimate of the number of species found in fossils could be too large because some fossils may have been mistaken to be new species, when they were actually parts of one that has been found already!
- The estimated number of living species could be much less than the real number. A recent estimate says that about 8.7 million species of plants and animals exist and that of all of the species living now, 86% of land species and 91% of sea species have not yet been discovered! Only around 1.2 million species have been identified.
Organisms rarely become fossils, and then only a tiny fraction of these have been discovered. The number of species that have become fossils compared to the number of species living now backs this up. It is therefore likely that at most 1% of animals that have ever lived have been found in fossils.
1st place (Year 11): Tom A.
Tom’s winning entry
When I was small, I dreamed of finding a fossilised dinosaur in my garden. Now I realise how unlikely it is to find a fossil, let alone a whole dinosaur. Indeed, palaeontologists believe that only one percent of species that have ever lived have been found as fossils. It’s interesting to think through why this might be.
To come up with an estimate for the percentage of fossilised species we need two numbers. The first is the total number of fossils that we have already found. This is easy to calculate because we can count the number of fossilised species in museums and private collections. This number is estimated to be 250,000. The second number for this calculation is harder to estimate. It’s the total number of species that have ever lived.
There are many ways to come up with the total number of species ever to have lived but maybe the most accurate is with computer simulations. We can enter all the information we know about climate, geology and events of the past into a program on a super computer. Then, we can run a simulation with that data including other factors of biology, chemistry and physics to fill in the gaps in our knowledge to predict the total number of species that have ever lived. This works fine for recent history, maybe the last million years, but it’s almost impossible to know how many species lived in the deep past because of patchy records.
However we don’t necessarily need to know the total number of species to know that less than one percent have been found as fossils. We know that there have been hundreds of millions of species on the earth and 250,000 is less than one percent of that. With this information palaeontologists can confidently say that less than one percent of species to ever live have been found as fossils. But why is that the case?
There are, in fact, many reasons why so few species have been found as fossils. To form a fossil, the conditions need to be just right so the bones are buried before natural processes destroy them. Then the rock they are fossilised in has to stay near the earth’s surface and not be subducted into the earth’s mantle. Lastly, the fossil must be in a place where we can have a chance to find it; on land where we have legal permission, accessible by foot or car, not under water or in a dense jungle to name a few possible restrictions. Maybe even more important than physical access is availability of funding and expertise to undertake excavations. All these factors contribute to the difficulty of discovering fossils.
So while we’ll never know of many of the species that have lived on Earth, it seems likely there are more fossils waiting to be found. My dreamed-of dinosaurs are still out there – maybe just not in my garden.
2nd place (Year 10)
2nd place (Year 11)
Finalists (Year 10)