New insight into what caused Earth’s first mass extinction

By Chukwuma Muanya   |   16 September 2015   |   11:06 pm  

Homo naledi has a mixture of primitive and more modern features CREDIT: John Hawks

• Scientists discover habitable rocky planets, new human species
• DNA from Neandertal relative may shake up family tree 

Scientists have provided new insight into what caused Earth’s first mass extinction even as they have also discovered new rocky habitable planets and new human species.

Also, in a remarkable technical feat, researchers have sequenced Deoxy ribonucleic Acid (DNA) from fossils in Spain that are about 300,000 to 400,000 years old and have found an ancestor—or close relative—of Neandertals.
According to Wikipedia, the Neanderthals or Neandertals were a species of human in the genus Homo that became extinct between 41,000 and 39,000 years ago. They were closely related to modern humans, differing in DNA by just 0.12 per cent. Remains left by Neanderthals include bone and stone tools, which are found in Eurasia, from Western Europe to Central and Northern Asia and the Middle East. Neanderthals are generally classified by biologists as the species Homo neanderthalensis, but a minority considers them to be a subspecies of Homo sapiens (Homo sapiens neanderthalensis).

Meanwhile, until now, mass extinctions have been associated with catastrophic events, like giant meteorite impacts and volcanic super-eruptions. But the world’s first known mass extinction, which took place about 540 million years ago, now appears to have had a more subtle cause: evolution itself.

The study is described in the paper “Biotic replacement and mass extinction of the Ediacara biota” published September 2 in the journal Proceedings of the Royal Society B.

Assistant professor of earth and environmental sciences at Vanderbilt University, Simon Darroch, said: “People have been slow to recognize that biological organisms can also drive mass extinction. But our comparative study of several communities of Ediacarans, the world’s first multicellular organisms, strongly supports the hypothesis that it was the appearance of complex animals capable of altering their environments, which we define as ‘ecosystem engineers,’ that resulted in the Ediacaran’s disappearance.”

Darroch added: “There is a powerful analogy between the Earth’s first mass extinction and what is happening today. The end-Ediacaran extinction shows that the evolution of new behaviors can fundamentally change the entire planet, and we are the most powerful ‘ecosystem engineers’ ever known.”

The earliest life on Earth consisted of microbes – various types of single-celled microorganisms. They ruled the Earth for more than three billion years. Then some of these microorganisms discovered how to capture the energy in sunlight. The photosynthetic process that they developed had a toxic byproduct: oxygen. Oxygen was poisonous to most microbes that had evolved in an oxygen-free environment, making it the world’s first pollutant.

But for the microorganisms that developed methods for protecting themselves, oxygen served as a powerful new energy source. Among a number of other things, it gave them the added energy they needed to adopt multicellular forms. Thus, the Ediacarans arose about 600 million years ago during a warm period following a long interval of extensive glaciation.

What scientists do know is that, in their heyday, Ediacarans spread throughout the planet. They were a largely immobile form of marine life shaped like discs and tubes, fronds and quilted mattresses. The majority were extremely passive, remaining attached in one spot for their entire lives. Many fed by absorbing chemicals from the water through their outer membranes, rather than actively gathering nutrients.
Paleontologists have coined the term “Garden of Ediacara” to convey the peace and tranquility that must have prevailed during this period. But there was a lot of churning going on beneath that apparently serene surface.

After 60 million years, evolution gave birth to another major innovation: animals. All animals share the characteristics that they can move spontaneously and independently, at least during some point in their lives, and sustain themselves by eating other organisms or what they produce. Animals burst onto the scene in a frenzy of diversification that paleontologists have labeled the Cambrian explosion, a 25-million-year period when most of the modern animal families – vertebrates, molluscs, arthropods, annelids, sponges and jellyfish – came into being.

Meanwhile, the quest for potentially habitable planets is often interpreted as the search for an Earth twin. And yet, some rocky planets outside our Solar System may in fact be more promising candidates for further research. Scientists from KU Leuven, Belgium, have run 165 climate simulations for exoplanets that permanently face their ‘sun’ with the same side. They discovered that two of the three possible climates are potentially habitable.

Most exoplanets orbit relatively small and cool stars known as red dwarfs. Only exoplanets that orbit close to their star can be warm enough for liquid water. What is more, being close to their star also makes these potentially habitable planets relatively easy to detect and observe for research purposes.

Many exoplanets that orbit closely to their stars always face that star with the same side. As a result, they have permanent day and night sides. And yet, the climate on these planets is not necessarily scorching hot on one side and freezing on the other. This is due to a very efficient ‘air conditioning system’ that keeps surface temperatures within the habitable range.

Dr. Ludmila Carone, Professor Rony Keppens, and Professor Leen Decin from KU Leuven, Belgium, have now examined the possible climates of these exoplanets in unprecedented detail. “On the basis of 3D models, we examined exoplanets with different rotation periods and sizes,” Ludmila Carone explains. “We discovered that these rocky planets have three possible climates, two of which are potentially habitable.”
On exoplanets with rotation periods under 12 days, an eastward wind jet known as superrotation forms in the upper layers of the atmosphere along the equator.

This wind jet interferes with the atmospheric circulation on the planet, so that its day side becomes too hot to be habitable. A second possible wind system is characterised by two weaker westward wind jets at high latitudes. The third climate option combines weak superrotation with two high-latitude wind jets. These last two wind systems do not interfere with the ‘air conditioning system’, so that the planets remain potentially habitable.

The findings provide valuable input for future space missions. Specifically, KU Leuven researchers are currently involved in the preparation of the James Webb Space Telescope mission (2018) – the Hubble successor – as well as the planet-finder mission PLATO (2024). Not only will the study help identify the most promising candidates for further research in our solar vicinity, it will also help avoid the premature discarding of potentially habitable planets that are worth investigating despite their ‘un-Earth-like’ appearance.
Meanwhile, scientists have discovered a new human-like species in a burial chamber deep in a cave system in South Africa. The discovery of 15 partial skeletons is the largest single discovery of its type in Africa.
The researchers claim that the discovery will change ideas about our human ancestors.

The studies, which have been published in the journal Elife also indicate that these individuals were capable of ritual behaviour.
The species, which has been named naledi, has been classified in the grouping, or genus, Homo, to which modern humans belong.
The researchers who made the find have not been able to find out how long ago these creatures lived – but the scientist who led the team, Prof Lee Berger, told BBC News that he believed they could be among the first of our kind (genus Homo) and could have lived in Africa up to three million years ago.

Like all those working in the field, he is at pains to avoid the term “missing link”. Prof Berger says naledi could be thought of as a “bridge” between more primitive bipedal primates and humans.

Meanwhile, the nuclear DNA, which is the oldest ever sequenced from a member of the human family, may push back the date for the origins of the distinct ancestors of Neandertals and modern humans, according to a presentation at the fifth annual meeting of the European Society for the study of human evolution.

Ever since researchers first discovered thousands of bones and teeth from 28 individuals in the mid-1990s from Sima de los Huesos (“pit of bones”), a cave in the Atapuerca Mountains of Spain, they had noted that the fossils looked a lot like primitive Neandertals.
The Sima people, who lived before Neandertals, were thought to have emerged in Europe. Yet their teeth, jaws, and large nasal cavities were among the traits that closely resembled those of Neandertals, according to a team led by paleontologist Juan-Luis Arsuaga of the Complutense University of Madrid.

As a result, his team classified the fossils as members of Homo heidelbergensis, a species that lived about 600,000 to 250,000 years ago in Europe, Africa, and Asia. Many researchers have thought H. heidelbergensis gave rise to Neandertals and perhaps also to our species, H. sapiens, in the past 400,000 years or so.

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