How many species live on Earth and in the ocean?

A validated taxonomic extrapolation estimates ~8.7 million eukaryotic species on Earth, with most still undescribed.

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What global species-richness estimate do authors report?

About 8.7 million species.

What prior expert range did ~8.7 million narrow?

About 3 to 100 million species.

What fraction of Earth species are catalogued?

About 14%.

What fraction of ocean species are catalogued?

About 9%.

Why estimate species totals?

Curiosity about diversity and a reference for biodiversity loss.

What problem has made past estimates controversial?

Incomplete sampling plus weak extrapolation methods.

What did authors’ approach add?

Validation against inventories and explicit statistical extrapolation.

What taxonomic issue did experts flag as major at species level?

Synonyms.

Why don’t prokaryotes dominate the known total?

Species concepts differ; known prokaryotes are a tiny share of named species.

How long has formal taxonomic classification been underway?

About 250 years.

What do authors expect better data to do to estimates?

Further diminish synonym/incompleteness problems and likely raise estimates.