Tuesday, 4 October 2016

An Unknown Comet Impact Caused The Evolution Of Our Earliest Ancestors, Say Geologists

Almost 56 million years ago, Earth experienced one of the greatest and significant warming events in its 4.5 billion year history. Temperatures increased by up to 8°C (14.4°F), and there was little to no ice anywhere in the world. During this period of constant warming, the first 'true' primates appeared, and set off the course that would ultimately lead to the evolution of humans. And now geologists say they have found signs that an unknown comet impact could have caused this crucial event.

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Almost about 56 million years ago, approximately 10 million years after the mass extinction of the non-avian dinosaurs, something caused an age of skyrocketing global temperatures. Known as the Paleocene-Eocene Thermal Maximum (PETM), this incident marked the end of the Paleocene Epoch and the creation of Eocene Epoch, which remained until about 33.9 million years ago. Many specialists deliberate the PETM to be the best earliest analog of modern climate revolution, because it saw atmospheric carbon dioxide levels intensify so rapidly, temperatures around the globe increased by 5°C to 8°C.

Oceanic surface temperatures in the tropics rose as high as 35°C, and sea-floor temperatures were 10°C higher than they are today. Oceans acidified, permafrost melted, wildfires ripped through the forests, and life developed to manage with the new conditions. Many land mammals were forced out of the plantations and into the open plains, letting them grow larger, and these groups made the basis of modern-day rhinoceroses, horses, camels, pigs, and hippopotamuses.

The antique ancestors of whales seem to have taken to the sea around this time, and placental animals with larger bodies and bigger brains than ever before initiated to appear in the fossil record. The first 'true' primates also settled during this time, with an ability to hold onto objects and branches with their hands and feet, something that would outline their monkey relatives numerous millions of years later.

But as essential as the PETM is to Earth’s history, what really triggered it has sustained one of the largest mysteries in geology. Now, teams’ geologists recommend that the impact of a small comet could have begun this global warming event, and say they have evidence of microscopic reflective spheres from up and down the US East Coast to back them up. Yep, just as an effect from a space rock laid an end to the lives of so many dinosaurs, 10 million years later, a similar incident could have ignited the evolution of numerous species of heat-loving plants and animals.

Morgan Schaller geologist and lead scientist, from the Rensselaer Polytechnic Institute in New York, told Thomas Sumner at Science News, "The timing is nothing short of remarkable". At the annual conference of the Geological Society of America in Colorado last month, Schaller and his team offered two papers explaining the discovery of weird silica 'beads' in eight sediment cores tied to the foundation of the PETM. They say these glassy spheres, discovered in three Atlantic Coastal Plain locations, are often related to extraterrestrial strikes, and they have been hiding in a plain scene for decades.

"The rock looked like micro-tektites; the remains formed and tossed separately when comets or asteroids strike Earth at high speeds. This was a shock to the team: these sediments had been considered many times before. The spheres may have mixed against the background of the black trays that are usually used to search for light-coloured forams, fossils of microscopic organisms."

These spheres are normally associated with volcanic outbreaks, one of the leading suppositions for what triggered the PETM. But the geologists says the water content of these micro-tektites is less than 0.03%, which is much lower than what’s been found in volcanic micro-tektites, and they hold inclusions of quartz glass that are characteristic of a hot impact. They also found that three of the PETM sediment centers enclosed large spikes of charcoal directly above the microtektite sheets, which suggests that right after their suggested impact come the spread of wildfires.

The team explained how this charcoal also comprises preserved remnants of burnt plants, which they say further supports their case.

They stated in one of the papers, "We conclude that the thermal anomalies resulting from the impact and eject a fallout possibly ignited common wildfires, evidence for which has been documented earlier from other Paleocene-Eocene segments globally."

The finding, which has yet to be peer-reviewed, was met with much debate at the meeting, with some geologists open to the idea that this actually is evidence of a life-altering comet impact, while others remain completely skeptical. A geologist from Lund University in Sweden, Birger Schmitz told Voosen, "It is a truly amazing discovery.   The data look sound."

Meanwhile, an oceanographer at Rice University in Houston, Jerry Dickens said,"I do not doubt that the spheres devised from an impact, or that the charcoal reduced from forest fires, but proposes that these spheres and charcoal can be found through the PETM sediment sheets, not just at the foundation".

The team now has to clarify how such a small impact, projected to be a couple kilometers across, could have generated such a planet-wide warming incident, but one chance is that it occurred to hit a massive carbon-filled area, such as natural oil reservoir. The panel's still out on this one, but if the scientists can discover more evidence to back up their claim, it could mean that not one, but two impacts started the chain of events that would give rise to our first ancestors.

You can read a summary of the both papers here and here.

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