The continents are: Australia, Antarctica, Africa, Asia, Europe, North America, South America and Zealandia.

Wait! Zealandia?

The geology world is abuzz with an earthly controversy to match the astronomy dilemma over demoting Pluto to nonplanet status. This geographical crisis emerged over the past decade as a growing group of geologists has come out in favor of continent status for an undersea platform off the northwest coast of New Zealand.

These geologists say that New Zealand is a part of a large, submerged continent, but unlike astronomers, who have an official body (the International Astronomical Union) to oversee the discovery and naming of celestial objects, geologists and geographers have no organization in charge of recognizing and naming a new continent.

Finding a new continent is a much rarer event, largely because continents are much rarer than stars.

The last continental discoveries were by Capt. James Cook, who found the first evidence for Antarctica during his second voyage from 1772 to 1775, and William Smith and Edward Bransfield, who some 50 years later first sighted the Antarctic shore.

Oddly, we know much less about the ocean floor than we know about space. Space is transparent, but the sea floor is invisible beneath miles of water. Direct sea-floor exploration involves great depth, tremendous pressure, corrosive salt water and near-freezing temperatures, so much of what we know comes from remote sensing.

Yet we have mapped many undersea ridges, most of them very small compared to a continent, and almost all are volcanic. What characterizes Zealandia is its granitic composition — very hard, granular igneous rock — and 94 percent of it is submerged. The islands of New Zealand, New Caledonia and a few other scattered islands peek above sea level.

That granitic composition is different from most seafloor rocks, which are basaltic in composition, like the Hawaiian Islands.

Granitic rocks are exclusively associated with continents because they can only form at the edges of continents where subduction pushes basaltic oceanic crust deep below the continental crust. There, heat and pressure chemically extract the lighter silica-rich components that bubble up and solidify before reaching the surface.

Zealandia is huge compared with most undersea features. Its size is comparable to the Indian subcontinent that stuck onto Asia when it collided with the big continent millions of years ago, forming the Himalaya Mountains.

There is no agreement on the status of Zealandia. Some note other large land masses, such as Madagascar, but Madagascar is only one-sixth the size of the proposed Zealandia continent.

Greenland might be large enough to be a continent, but it is only half the size of Zealandia, and there is general agreement that it is not distinct from nearby North America.

All of the discussion, conversation, debate and argument over this may seem trivial to the layman, but visualizing Zealandia as a separate continent can help scientists solve the continental jigsaw puzzle, and study how geologic forces reshape continental landmasses over time.

Out of this discussion may arise a new definition of “continent” and “mini-continent,” the latter of which could include subcontinents such as India, Greenland and Madagascar, along with Zealandia.

Without a standard definition of what a continent is, there is no global agreement on the number of continents. Geologists consider Europe to be part of the Eurasian continent, while Europeans consider North and South America to be one large continent.

Richard Brill is a professor of science at Honolulu Community College. His column runs on the first and third Fridays of the month. Email questions and comments to brill@hawaii.edu.