There are currently over 8 billion humans on the planet. Although that is a remarkable number, it is still just a fraction of the number of people who ever lived on Earth and even a smaller portion of the total number of animals that have ever existed.
What is the Total Number of Existing Animal Species?
It is not easy to estimate the number of animals on Earth, let alone determine how many have existed on our planet throughout its history. According to geophysical researcher David Jablonski from the University of Chicago, the calculation might be a difficult one, but it is probably easiest to begin by estimating the total number of animal species.
As of 2022, about 2.16 million animal species have been formally described, according to the IUCN Red List. However, a 2013 study suggests that up to 20% of those animals could be duplicated or documented by multiple scientists. If this estimate is accurate, the number of known animal species is just around 1.7 million.
This number is not static. Every year, scientists continue to describe 14,000 to 18,000 new animal species. Experts have only scratched the surface of the number of animals on Earth.
In 2011, biogeographer Camilo Mora from the University of Hawaii and his colleagues conducted research, which led them to estimate the total number of eukaryotes on the planet. Their final count was around 8.7 million, about 7.7 million animals. Of this population, roughly half were insects.
To find out the total number of animal species that have ever lived, we must look into the past using fossil records. Life appeared on Earth about 3.7 billion years ago. Since the first life forms were very simple cells, it would be another 1.4 billion years before multicellular organisms appeared. It can be concluded that animals evolved even more recently, around 800 million years ago.
Some early animals are preserved in the fossil record, but most are not. This is because soft-bodied species rarely keep, while hard-bodied creatures only use fossilization under particular conditions. Furthermore, plate tectonics slowly and continuously changes the planet's landscape, erasing old impressions, stone, and bone.
According to Jablonski, the standard estimate is that 99.9% of species that have ever lived are extinct, although it is just a crude approximation. Assuming this approximation is correct, experts must multiply 7.7 million by nearly 100%. That puts the total number of animals at more or less 770 million species.
How Many Individual Animals Have Ever Lived on Earth?
Humans share Earth with around 130 billion other mammals, up to 428 million birds, 3.5 trillion fish, and ten quintillion insects. Assuming that the current abundances have been stable over the Earth's history, experts can extrapolate out using the relative proportions of the 7.7 million existing species.
For instance, if there are currently 3.85 million species of insects on Earth, that number corresponds to 385 million in the past. Multiplying 385 million to 10 quintillion, we have an estimate of 3.85 x 10627 insects.
Since the insects are so ubiquitous, that estimate may not be too far from the total number. If the other arthropods, invertebrates, and vertebrates are included, then we can estimate that there have been around 4.5x10^27 animals that have ever existed on Earth.
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