Asteroids and comets that repeatedly smashed into the early Earth covered the planet's surface with molten rock during its earliest days, but still may have left oases of water that could have supported the evolution of life, scientists say.
The new study reveals that during the planet's infancy, the surface of the Earth was a hellish environment, but perhaps not as hellish as often thought, scientists added.
Earth formed about 4.5 billion years ago. The first 500 million years of its life are known as the Hadean Eon. Although this time amounts to more than 10 percent of Earth's history, little is known about it, since few rocks are known that are older than 3.8 billion years old. [How the Earth Formed: A History]
Earth's Violent Youth
For much of the Hadean, Earth and its sister worlds in the inner solar system were pummeled with an extraordinary number of cosmic impacts.
"It was thought that because of these asteroids and comets flying around colliding with Earth, conditions on early Earth may have been hellish," said lead study author Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colorado. This imagined hellishness gave the eon its name — Hadean comes from Hades, the lord of the underworld in Greek mythology.
However, in the past dozen years or so, a radically different picture of the Hadean began to emerge. Analysis of minerals trapped within microscopic zircon crystals dating from this eon "suggested there was liquid water on the surface of the Earth back then, clashing with the previous picture that the Hadean was hellish," Marchi said. This could explain why the evidence of the earliest life on Earth appears during the Hadean — maybe the planet was less inhospitable during that eon than previously thought.