What Ecological Impact Did A Meteor Strike 800,000 Years Ago In SE Asia Have?

About a million years after Homo Erectus arrives in Southeast Asia and East Asia from Africa, and probably before or at around the same time as, the appearance of a common ancestor of Neanderthals and Denisovans, and maybe even a common ancestor of that clade and modern humans an asteroid slams into Southeast Asia causing immense short term climate effects, although not a mass extinction. There has been no bigger impact on Earth since then. Three mysteries remain.

First, where precisely was the impact crater? 

The event has been known to scientists in the field for many years, but the latest discoveries narrow the search to Southeast Asia, in someplace where erosion and the like would make the impact site less obvious than it would otherwise be.

Second, what ecological impact did it have?

There isn't much in the archaeological or fossil record to indicate that this was associated with a mass extinction event or a major ecological shift, but this record, particular in Southeast Asia, is very thin. 

A kilometer-size asteroid slammed into Earth about 800,000 years ago with so much force that it scattered debris across a 10th of our planet’s surface. Yet its impact crater remains undiscovered. Now, glassy remains believed to have come from the strike suggest the asteroid hit southeast Asia as our close ancestors walked the Earth.

“This impact event is the youngest of this size during human evolution with likely worldwide effects,” says Mario Trieloff, a geochemist at the University of Heidelberg in Germany not involved in the research. Large impacts can disrupt Earth’s climate by spewing dirt and soot high into the atmosphere, where it can block sunlight for months or even years. . . .

They’re puzzled why a crater that’s both presumably large and geologically young—meaning it hasn’t been exposed to much erosion due to rain and wind—hasn’t been found. The crater, if discovered, could also shed light on how the impact affected life nearby. “Our not-too-distant ancestors witnessed this impact,” Cavosie says. “They might have been dragging their knuckles, but an event like the formation of a 50- to 100-kilometer-diameter impact is sure to have gotten their attention.”

Third, is it plausible that this impact created conditions that spurred the evolution of Neanderthals, Denisovans and maybe even modern humans as well, by placing greater demands for intelligence and adaptability on the hominins in existence at the time?

While this particular data point is hardly conclusive and really no more than a conjecture, collectively, the evidence points pretty strongly towards key moments of punctuated change driven by climate and extraterrestrial events in what is known as the Court Jester Hypothesis.

From Science Magazine.

Australasian tektites are enigmatic drops of siliceous impact melt found in an ~8000 × ~13,000 km strewn field over Southeast Asia and Australia, including sites in both the Indian and Pacific oceans. These tektites formed only 790,000 yr ago from an impact crater estimated to be 40–100 km in diameter; yet remarkably, the young and presumably large structure remains undiscovered. 

Here we report new evidence of a rare high-pressure phase in Australasian tektites that further constrains the location of the source crater. The former presence of reidite, a high-pressure polymorph of zircon, was detected in granular zircon grains within Muong Nong–type tektites from Thailand. The zircon grains are surrounded by tektite glass and are composed of micrometer-sized neoblasts that contain inclusions of ZrO2. Each grain consists of neoblasts in three distinct crystallographic orientations as measured by electron backscatter diffraction, where all directions are orthogonal and aligned with one direction from the other two orientations. The systematic orientation relationships among zircon neoblasts are a hallmark of the high-pressure polymorphic transformation to reidite and subsequent reversion to zircon. The preserved microstructures and dissociation of zircon to ZrO2 and SiO2 require a pressure >30 GPa and a temperature >1673°C, which represent the most extreme conditions thus far reported for Australasian Muong Nong–type tektites. The data presented here place further constraints on the distribution of high-pressure phases in Australasian tektites, including coesite and now reidite, to an area centered over Southeast Asia, which appears to be the most likely location of the source crater.

Aaron J. Cavosie, et al. "New clues from Earth's most elusive impact crater: Evidence of reidite in Australasian tektites from Thailand" Geology (December 20, 2017).