First, it was Mauritia, based on 3-billion-year-old samples of the volcanic rock zircon, found on the solid rock of the tiny island of Mauritius, leading scientists to conclude that what lies beneath the current-day territory was once a large continent that stretches for many miles along the sea floor. Scientists concluded that Mauritia was once a supercontinent that included what is now both India and Madagascar.

Now, it's Zealandia, a 2-million-square-mile underwater landmass that includes both New Caledonia and New Zealand, which are 1,500 miles apart. Scientists now think that both current countries and the land that lies underneath the ocean between once belonged to one large chunk of (above-the-waves) land that they're calling Zealandia. Today, 94 percent of the landmass is underwater.

The connection is that both of these newly discovered "subcontinents" were once part of an even larger landmass, Gondwanaland, which itself predated then formed part of the supercontinent Pangaea. Subsequent breakups of the very large landmasses, coupled with an ice age or two, resulted in the formation of today's continents.

Geologists have instituted a few guidelines for defining continent but have no strict definition. One of the most widely repeated definitions is that a continent is a large, continuous landmass separated from other land by water. By that definition, perhaps Greenland is a continent, instead of being "only" the world's largest island (that isn't a continent).

As well, many people view Europe and Asia as one continent, Eurasia, while other people view North America, Central America, and South America as one large continent called the American continent. Others prefer to include not only Australia but New Zealand and a few other Pacific nations and call them by the collective name of Oceania.

However, the most widely preferred list of Earth's continents is this:

• Africa
• Antarctica
• Asia
• Australia
• Europe
• North America
• South America.

A separate team of scientists reported the discovery of each "new" continent, along with evidence to back up the announcements. It remains to be seen whether the scientific community as a whole embraces the idea of increasing the "official" number.