As you can see, our planet really is home to an incredible diversity of creatures.

According to the team at Our World in Data, a scientific online publication that focuses on large global problems such as poverty, disease, hunger, climate change, existential risks, and inequality, there are several ways we can answer the question of how much life is on Earth.

We could, for instance, count the number of species, population sizes or the number of individual organisms, but these metrics can make it difficult to compare between taxa: small organisms may have a large population but still account for a very small percentage of Earth's organic matter.

For a meaningful comparison, we can, instead, look at biomass—it is measured in tonnes of carbon as it is a key building-block of life. In this case:

• plants – mainly trees – dominate Earth: they account for more than 82% of biomass;
• surprisingly in second place is the life we cannot see: tiny bacteria sum up to 13%;
• whilst our perceptions are often focused on the animal kingdom, it accounts for only 0.4%;
• humans make up just 0.01% of biomass, so we'd need about 70 trillion of us to match the Earth’s collective biomass.

But if we want to get more specific, then we can start with the International Union for Conservation of Nature (IUCN) Red List. It tracks the number of described species and updates the figure annually based on the latest work of taxonomists.

In 2021, it listed 2.13 million species on the planet, including 1.05 million insects, over 83,000 mollusks, over 11,000 birds, and over 6,000 mammals. These figures, however, might be a bit too high. This is because some species end up being synonyms – the description of already-known species, simply given a separate name.

There is a continual evaluation process to remove synonyms (and most are eventually), but often, species are added at a faster rate than synonyms can be found and removed.

To get a sense of how big this problem is, consider this: one study estimated that around 20% of the described species were undiscovered duplicates. The paper estimated that the 1.9 million described species at the time was actually closer to 1.5 million unique species.

If we were to assume this 20% figure to be true, our 2.12 million described species might actually be closer to just 1.7 million.

Either way, academics believe that these numbers are still an underestimate. One of the most widely-cited figures comes from Camila Mora and colleagues. They suggest that there are around 8.7 million species on Earth today, with 2.2 million of them living in the ocean.

As Robert May said in a paper published in Science:

"If some alien version of the Starship Enterprise visited Earth, what might be the visitors' first question? I think it would be: 'How many distinct life forms—species—does your planet have?' Embarrassingly, our best-guess answer would be in the range of 5 to 10 million eukaryotes (never mind the viruses and bacteria), but we could defend numbers exceeding 100 million, or as low as 3 million."

At first, it doesn't seem like a big deal, but the fact that there are so many species that we've yet to discover has real consequences for our ability to understand changes in global biodiversity and the rate of species extinctions. If we don't know that certain species exist, we also don't know that they might have, or will soon, disappear. Some animals will inevitably go extinct before we realize that they existed.