Which Ancient Minerals on Early Earth Gave Rise to Life?

When life first emerged on Earth, primitive organisms exploited our planet's raw materials. In fact, scientific models almost always look to minerals for essential tasks for life, such as the synthesis of molecular building blocks or the supply of metabolic energy. However, these models assume that the minerals found on Earth today are the same as they were 550 million years ago. Now, scientists have discovered new evidence that challenges that assumption.

Life first emerged during the Hadean Eon, millions of years ago. Needless to say, Earth has changed quite a bit since then. The atmosphere has undergone relatively rapid shifts in composition, so it's not surprising that minerals have also changed. In order to examine exactly what the minerals might have been like back then, the researchers compiled a list of every plausible mineral species on the Hadean Earth. In the end, they found that no more than 420 different minerals--just eight percent of the nearly 5,000 species that occur today--would have been present on our planet at that time.

"This is a consequence of the limited ways that minerals might have formed prior to four billion years ago," said Robert Hazen, one of the researchers, in a news release. "Most of the 420 minerals of the Hadean Eon formed from magma--molten rock that slowly crystallized at or near Earth's surface--as well as the alteration of those minerals when exposed to hot water."

While the composition may have been different, though, it doesn't change models too much. The most commonly invoked minerals in origin-of-life models were also present on early Earth. For example, clay minerals were certainly available along with sulfide minerals, including reactive iron and nickel varieties. These could catalyze organic reactions. That said, rare elements such as borate and molybdate minerals were most likely not present at the time; this, in turn, calls into question origin models that rely on these minerals groups.

The findings help show exactly what minerals would have been available at the time for the origins of life. In addition, they reveal what models would not have worked during this early Earth scenario. The research also raises the question of how other planets and moons evolved mineralogically.

The findings are published in the American Journal of Science.