Most of the Earth's surface is an ocean. When I think of the Earth, it is our oceans that I picture. Life began there.
We began there. Most of the major animal groups can trace their lineage back to the seas and the Cambrian explosion, an orgy of breathtaking species diversification.
Since that time, a shocking half a billion years ago, our seas have played host to an astonishing array of species. If I'd visited our Earth back in the Cambrian, I would have bet good money that our watery planet's future was in the seas not on the land. But that 's not the case. Quite surprisingly, it is our humble rock and soil who now boast more species. Five times that of those living in the oceans. I know, shocking but true. Our oceans certainly had the running start on both numbers and diversity of species. But it is our fungi, our flowering plants, mindblowing variety of insects, trees, bees and fleas that make up the bulk of Earth's species these days.
It is something I'm interested in learning more about as it does not make good sense to me. 80 percent of Earth's species live on land today. About 15 percent call our oceans home and another 5% or so live in freshwater. Why more species live on land than in the ocean has puzzled others as well. Robert May, a zoologist at the University of Oxford, mulls this very question in an article from 1994 titled, “Biological Diversity: Differences between Land and Sea.” He continued with his research and published "The future of biological diversity in a crowded world," in Current Science, Vol. 82, No. 11 (10 June 2002), pp. 1325-1331.
Here he questions how well we know the plants, animals and micro-organisms with which we share this beautiful planet. His focus in the paper was to question how many species are there and how fast are some going extinct? You'll be interested to know that his best guess in 2002 was somewhere between 1.7 to 1.8 million. That's a considerable increase from Carl Linneaus' work back in 1758, the Swedish botanist, zoologist, and physician took a stab at the same question and came up with an estimate of about 9,000 species. While his numbers were off by a long margin, he did give us the binomial nomenclature system we use for naming organisms, so he still gets a hall pass.
May is a boy about town. His work is referenced everywhere. You may enjoy an article by the Atlantic from 2017 that delves into the topic for the lay audience with an eye to popularized reading. May, R. (2002). The future of biological diversity in a crowded world. Current Science, 82(11), 1325-1331. Retrieved from http://www.jstor.org/stable/24105996 / The Atlantic article: https://www.theatlantic.com/science/archive/2017/07/why-are-there-so-many-more-species-on-land-than-in-the-sea/533247/
