Was Our Planet Really Once a Hell on Earth?

For the first 500 million years of its existence, our planet was believed to literally be a hell on Earth. But new research shows that this early Earth may have been surprisingly similar to the present day, complete with oceans, continents and active crustal plates.

This alternate view of Earth's first geologic eon, called the Hadean, is based on a comparison of zircon crystals formed four billion years ago with those formed during the same time period in Iceland. This icy country is supposedly what early Earth geological conditions were like, and so serves as a sort of blueprint for scientists studying the beginnings of our planet.

"We reasoned that the only concrete evidence for what the Hadean was like came from the only known survivors: zircon crystals -- and yet no one had investigated Icelandic zircon to compare their telltale compositions to those that are more than 4 billion years old, or with zircon from other modern environments," lead researcher Calvin Miller of Vanderbilt University said in a statement.

Until 30 years ago, scientists thought the Hadean period was hellishly hot, and Earth was covered by a giant "magma ocean." This view was based on the fact that they could never find rock formations from that time period, jumping to the conclusion that the intense heat melted the rocks, leaving behind no trace.

But then geologists discovered zircon crystals - a mineral typically associated with granite - preserved in younger sandstones. Radiometric dating and other analytical techniques allowed the researchers to study early Earth's crust via these four-billion-year-old crystals, as well as extract information about the environment in which the crystals formed, including the temperature and whether water was present.