Early Earth: A Battered, Hellish World with Water Oases for Life

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.

An artistic conception of the early Earth-moon system showing the Earth's surface after being bombarded with large impacts, causing magma extrusion on the surface, though some liquid water was retained. Image released on July 30, 2014. 

Credit: Simone Marchi

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.

Simone Marchi

This imagined hellishness gave the eon its name, Hadean comes from the word 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.

This artist's illustration shows a close-up of the early Earth, revealing magma extrusion on the surface and the scars from severe cosmic bombardment. Image released on July 30, 2014.

Credit: Simone Marchi

Cosmic bombardment history
The exact timing and magnitude of the impacts that smashed Earth during the Hadean are unknown.

To get an idea of the effects of this bombardment, Marchi and his colleagues looked at the moon, whose heavily cratered surface helped model the battering that its close neighbour Earth must have experienced back then.

"We also looked at highly siderophile elements (elements that bind tightly to iron), such as gold, delivered to Earth as a result of these early collisions, and the amounts of these elements tells us the total mass accreted by Earth as the result of these collisions," Marchi said.

Prior research suggests these impacts probably contributed less than 0.5 percent of the Earth's present-day mass.

The researchers discovered that "the surface of the Earth during the Hadean was heavily affected by very large collisions, by impactors larger than 100 kilometers (60 miles) or so, really, really big impactors," Marchi said.

"When Earth has a collision with an object that big, that melts a large volume of the Earth's crust and mantle, covering a large fraction of the surface," Marchi added.

These findings suggest that Earth's surface was buried over and over again by large volumes of molten rock, enough to cover the surface of the Earth several times. This helps explain why so few rocks survive from the Hadean, the researchers said.

However, although these findings might suggest that the Hadean was a hellish eon, the researchers found that "there were time gaps between these large collisions," Marchi said.

"Generally speaking, there may have been something on the order of 20 or 30 impactors larger than 200 km (120 miles) across during the 500 million years of the Hadean, so the time between such impactors was relatively long," Marchi said.

Any water vapourised near these impacts "would rain down again," Marchi said, and "there may have been quiet tranquil times between collisions, there could have been liquid water on the surface."

The researchers suggested that life emerging during the Hadean was probably resistant to the high temperatures of the time.

Marchi and his colleagues detailed their findings in the July 31 issue of the journal Nature.

More Information: Widespread mixing and burial of Earth’s Hadean crust by asteroid impacts. - Authors: S. Marchi, W. F. Bottke, L. T. Elkins-Tanton, M. Bierhaus, K. Wuennemann, A. Morbidelli & D. A. Kring - doi:10.1038/nature13539

Nanoparticles found in moon glass bubbles explain weird lunar soil behaviour

A stunning discovery by Queensland University of Technology (QUT) soil scientist Marek Zbik of nano particles inside bubbles of glass in lunar soil could solve the mystery of why the moon's surface topsoil has many unusual properties.

Dr Zbik, from Queensland University of Technology's Science and Engineering Faculty, said scientists had long observed the strange behaviour of lunar soil but had not taken much notice of the nano and submicron particles found in the soil and their source was unknown.

Dr Zbik took the lunar soil samples to Taiwan where he could study the glass bubbles without breaking them using a new technique for studying nano materials call synchrotron-based nano tomography to look at the particles. Nano tomography is a transmission X-ray microscope which enables 3D images of nano particles to be made.

"We were really surprised at what we found," Dr Zbik said.

"Instead of gas or vapour inside the bubbles, which we would expect to find in such bubbles on Earth, the lunar glass bubbles were filled with a highly porous network of alien-looking glassy particles that span the bubbles' interior.

"It appears that the nano particles are formed inside bubbles of molten rocks when meteorites hit the lunar surface. Then they are released when the glass bubbles are pulverised by the consequent bombardment of meteorites on the moon's surface.

"This continuous pulverising of rocks on the lunar surface and constant mixing develop a type of soil which is unknown on Earth."

Dr Zbik said nano particles behaved according to the laws of quantum physics which were completely different from so called 'normal' physics' laws. Because of this, materials containing nano particles behave strangely according to our current understanding.

"Nano particles are so tiny, it is their size and not what they are made of that accounts for their exceptional properties.

"We don't understand a lot about quantum physics yet but it could be that these nano particles, when liberated from their glass bubble, mix with the other soil constituents and give lunar soil its unusual properties.

"Lunar soil is electro-statically charged so it hovers above the surface; it is extremely chemically active; and it has low thermal conductivity eg it can be 160 degrees above the surface but -40 degrees two metres below the surface.

"It is also very sticky and brittle such that its particles wear the surface off metal and glass."
Dr Zbik said the moon had no atmosphere to cushion the impact of meteorites like Earth had.

"When they hit the moon there is a very violent reaction. Huge temperatures are generated which melts the rock. The pressure goes and a vacuum is created. Bubbles occur in the molten glass rock like soft drink bubbles trying to escape the bottle.

"Our work now is to understand how those particles evolve from this process. It may also lead us to completely different way of manufacturing nanomaterials."

Dr Zbik and his research team's study was published in the International Scholarly Research Network Astronomy and Astrophysics.

To find out more and also view a 3D image from inside the lunar bubble using transmission X-Ray microscopy go to http://youtu.be/omRoS2SntMU. You can see what is inside the lunar bubble with 3D glasses.

Related Links: Queensland University of Technology