There are more than 8 billion people on the planet today, and while this is an impressive number, it is only a fraction of the total number of humans that have ever lived, and an even smaller fraction of the total number of animals that have ever lived. to meet.

How to estimate the number of animals

But how can scientists estimate the total number of animals on Earth, let alone determine how many animals have existed on our planet throughout its history? Geophysicist David Jablonski from the University of Chicago says it is necessary to start by estimating the total number of animal species.

According to estimates, approximately 2.16 million animal species have been officially identified by 2022. However, it is likely that up to 20% of these are duplicates documented by more than one scientist at the same time. Assuming this estimate is correct, the actual number of known animal species is around 1.7 million.

In 2011, biogeographer Camilo Mora of the University of Hawaii and his colleagues wrote a paper in the journal PLOS Biology that counted the total number of eukaryotic species on Earth (species whose cells have nuclei and organelles, unlike prokaryotes). do not). The final count showed approximately 8.7 million; about these 7.7 million of which are animals. About half of them are insects.

But to find out how many animal species have ever lived, we need to look into the past using fossils, and this presents us with a new set of challenges.

A journey to the past

• Life appeared on Earth 3.7 billion years ago, but the first organisms were very simple cells.
• Another 1.4 billion years passed before multicellular life emerged.
• Animals probably appeared later, around 800 million years ago.

Some of these early animals survive in the fossil record, but the vast majority do not. The truth is that soft-bodied species are rarely preserved, and hard remains petrify only under very specific conditions. Additionally, plate tectonics slowly and continuously moves the planet’s surface, erasing old tracks, stones, and bones. When two plates meet, they can begin to sink into the planet’s interior and melt into the bowels.

Scientists say that 99.9% of the species that have ever lived are extinct. This is a very rough estimate, but assuming this assumption is correct, we simply multiply 7.7 million by almost 100 percent. This means that the total number of animal species is approximately 770 million species.

So how can we count the number of individual animals that have ever lived on Earth? This number will be huge.

If we assume that current abundance has been relatively stable throughout the history of life, then we can apply relative proportions starting from the 7.7 million extant species. For example, if there are 3.85 million species of insects on Earth now, this corresponds to 385 million in the past, and if 385 million is multiplied by 10 quintillion individuals, 3.85×10²⁷ vermin.

We can extrapolate this (very roughly) to other arthropods, invertebrates, and vertebrates. about 4.5 x 10 of them lived on Earth²⁷ animals.

What is all this for?

All these calculations are of course approximate and based mostly on assumptions and theories. Why are you trying so hard to count the number of animals on the planet? It is important for scientists to understand the baseline level and fluctuations of Earth’s biodiversity. As a result of climate change, deforestation, pollution and other factors, we are heading towards a massive mass extinction that exceeds the rates of any that came before. To understand the scale of our current crisis, we need to know the background extinction rate.