Dublin's Trinity geologists re-write Earth's evolutionary history books

The study site landscape is shown with boulders of the paleosol in the foreground. 

Credit: Quentin Crowley

Geologists from Trinity College Dublin have rewritten the evolutionary history books by finding that oxygen-producing life forms were present on Earth some 3 billion years ago, a full 60 million years earlier than previously thought.

These life forms were responsible for adding oxygen (O2) to our atmosphere, which laid the foundations for more complex life to evolve and proliferate.

Working with Professors Joydip Mukhopadhyay and Gautam Ghosh and other colleagues from the Presidency University in Kolkata, India, the geologists found evidence for chemical weathering of rocks leading to soil formation that occurred in the presence of O2.

Using the naturally occurring uranium-lead isotope decay system, which is used for age determinations on geological time-scales, the authors deduced that these events took place at least 3.02 billion years ago.

The ancient soil (or paleosol) came from the Singhbhum Craton of Odisha, and was named the 'Keonjhar Paleosol' after the nearest local town.

The pattern of chemical weathering preserved in the paleosol is compatible with elevated atmospheric O2 levels at that time.

Such substantial levels of oxygen could only have been produced by organisms converting light energy and carbon dioxide to O2 and water.

This process, known as photosynthesis, is used by millions of different plant and bacteria species today.

It was the proliferation of such oxygen-producing species throughout Earth's evolutionary trajectory that changed the composition of our atmosphere, adding much more O2, which was as important for the development of ancient multi-cellular life as it is for us today.

Quentin Crowley, Ussher Assistant Professor in Isotope Analysis and the Environment in the School of Natural Sciences at Trinity, is senior author of the journal article that describes this research which has just been published online in Geology, the world's top-ranked Geology journal.

He said: "This is a very exciting finding, which helps to fill a gap in our knowledge about the evolution of the early Earth. This paleosol from India is telling us that there was a short-lived pulse of atmospheric oxygenation and this occurred considerably earlier than previously envisaged."

Credit: Quentin Crowley

The early Earth was very different to what we see today. Our planet's early atmosphere was rich in methane and carbon dioxide and had only very low levels of O2.

The widely accepted model for evolution of the atmosphere states that O2 levels did not appreciably rise until about 2.4 billion years ago.

This 'Great Oxidation Event' event enriched the atmosphere and oceans with O2, and heralded one of the biggest shifts in evolutionary history.

More Information: "Oxygenation of the Archean atmosphere: New paleosol constraints from eastern India" Joydip Mukhopadhyay1, Quentin G. Crowley: First published online August 28, 2014, doi: 10.1130/G36091.1

NASA Evolutionary Xenon Thruster (NEXT) Project sets new record

While the Dawn spacecraft is visiting the asteroids Vesta and Ceres, NASA Glenn has been developing the next generation of ion thrusters for future missions.

NASA's Evolutionary Xenon Thruster (NEXT) Project has developed a 7-kilowatt ion thruster that can provide the capabilities needed in the future.

Schematic of a Hall effect thruster electric propulsion device

An ion thruster produces small levels of thrust relative to chemical thrusters, but does so at higher specific impulse (or higher exhaust velocities), which means that an ion thruster has a fuel efficiency of 10-12 times greater than a chemical thruster.

The higher the rocket's specific impulse (fuel efficiency), the farther the spacecraft can go with a given amount of fuel.

Given that an ion thruster produces small levels of thrust relative to chemical thrusters, it needs to operate in excess of 10,000 hours to slowly accelerate the spacecraft to speeds necessary to reach the asteroid belt or beyond.

Diagram of how a gridded electrostatic ion engine (Kaufman type)

The NEXT ion thruster has been operated for over 43,000 hours, which for rocket scientists means that the thruster has processed over 770 kilograms of xenon propellant and can provide 30 million-newton-seconds of total impulse to the spacecraft.

This demonstrated performance permits future science spacecraft to travel to varied destinations, such as extended tours of multi-asteroids, comets, and outer planets and their moons.

Image Credit: NASA

Christopher Stringer: Rethinking "Out Of Africa"

CHRISTOPHER STRINGER: is one of the world's foremost paleoanthropologists.

He is a founder and most powerful advocate of the leading theory concerning our evolution: Recent African Origin or "Out of Africa".

He has worked at The Natural History Museum, London since 1973, collaborating with scientists across all the disciplines of paleoanthropology, and is a Fellow of the Royal Society, with over 200 papers and books to his name.

"At the moment, I'm looking again at the whole question of a recent African origin for modern humans—the leading idea over the last 20 years.

This argues that we had a recent African origin, that we came out of Africa, and that we replaced all of the other human forms that were outside of Africa.

But we're having to re-evaluate that now because genetic data suggest that the modern humans who came out of Africa about 60,000 years ago probably interbred with Neanderthals, first of all, and then some of them later on interbred with another group of people called the Denisovans, over in south eastern Asia.

If this is so, then we are not purely of recent African origin. We're mostly of recent African origin, but there was contact with these other so-called species.

We're having to re-evaluate the Out-of-Africa theory, and we're having to re-evaluate the species concepts we apply, because in one view of thinking, species should be self-contained units.

They don't interbreed with other species. However, for me, the whole idea of Neanderthals as a different species is really a recognition of their separate evolutionary history—the fact that we can show that they evolved through time in a particular direction, distinct from modern humans, and they separated maybe 400,000 years ago from our lineage

Morphologically we can distinguish a relatively complete Neanderthal fossil from any recent human.

You could argue that they're an extreme variant of Homo sapiens, but a very different 'race' from anyone alive today, or, as I prefer to argue, they're a separate species, with a separate evolutionary history.

I've never actually said that that meant they were completely reproductively isolated from us. We know that many closely related species in primates, for example, can interbreed.

Various species of monkey can interbreed and have fertile offspring, and so can our closest living relatives, Bonobos and common chimpanzees.

In my view the Neanderthals were closely related and probably potentially able to interbreed with modern humans, but until recently I considered that while there could have been interbreeding forty or fifty thousand years ago, it was on such a small scale that all trace of it vanished in the intervening years.

It now seems from Neanderthal genome studies that that was not so. We do have a bit of Neanderthal in us, you and I, it's a small amount, but certainly not negligible.

Does that mean Neanderthals are a different species or does it mean we should include them in Homo sapiens?

Well, they are still only a small part of our makeup now, reflecting something like a 2.5% input of their DNA. Physically, however, they went extinct about 30,000 years ago.

They had distinct behaviour and they evolved under different conditions from us, so I still think it's useful to keep them as a separate species, even if we remember that that doesn't necessarily preclude interbreeding."

Read more of this fascinating article here at EDGE: Rethinking 'Out of Africa' - Includes a Video and audio transcript.

Hammerhead sharks - Evolutionary process

For over a century, scientists have speculated why hammerheads evolved such an odd shape and whether having eyes so far apart would enhance their vision.

In 1942 a leading authority on sharks, Gordon Walls, suggested the position of the shark's eyes prevented it from having binocular vision but others have argued exactly the opposite, saying the animals must have enhanced eyesight.

Now, hammerhead sharks have had their first eye examination, and it has laid the debate to rest. Sharks with wider heads have better binocular vision – all the better to track fast-moving prey like squid with far more accuracy than sharks with close-set eyes.

The research also shows that hammerheads – among other sharks – have a 360-degree view of the world in the vertical plane, allowing them to simultaneously see prey above and below them.