[meteorite-list] Geologists To Drill into Heart of Dinosaur-Killing Impact (Chicxulub Crater)

[Ron Baalke]

http://www.nature.com/news/geologists-to-drill-into-heart-of-dinosaur-killing-impact-1.19643 

Geologists to drill into heart of dinosaur-killing impact

Quest aims to uncover secrets of big craters across the Solar System.

Alexandra Witze
Nature News
31 March 2016

The asteroid that created Chicxulub crater reshaped life on Earth.

Geophysicists are returning to Earth's most famous cosmic bullseye. 
Around 7 April, from a drill-ship off the coast of Yucatan, Mexico, they 
will start to penetrate the 200-kilometre-wide Chicxulub crater, which 
formed 66 million years ago when an enormous asteroid smashed into the 
planet. The aftermath of the impact obliterated most life on Earth, including 
the dinosaurs.

The expedition is the first to directly probe one of Chicxulub's most 
striking features - its "peak ring", a circle of mountains that 
rises within the crater floor. Scientists have yet to fully explain how 
peak rings form, even though they are common in big impact craters across 
the Solar System.

At Chicxulub, researchers will look for evidence to explain how a 14-kilometre-wide 
asteroid could have punched a hole that pushed rocks from the surface 
down some 20-30 kilometres. Flowing like liquid, the rocks then rebounded 
towards the sky - reaching as far as 10 kilometres above the original 
ground level - and finally splattered down to form a peak ring.

All of this happened in the span of several devastating minutes, says 
Joanna Morgan, a geophysicist at Imperial College London and the project's 
co-chief scientist. "It's astounding."

If the 2-month expedition goes as planned, it will bore 1,500 metres into 
sea-floor rocks. The drill will first pass through carbonate rocks that 
make up the bottom of the Gulf of Mexico (see map), and eventually reach 
the fractured "impact breccias" that represent the obliterating impact.

At least a dozen other boreholes and several oil-exploration wells have 
already penetrated the parts of Chicxulub that lie on land. They include 
a 1,511-metre-long core drilled near the crater rim in 2001-02 by a 
large international scientific consortium1. When combined with seismic 
surveys2, analyses of existing cores reveal a complex picture of nested 
rings of shattered rock, all created on a very bad day for life on Earth3.

Inner circle

The latest project will be the first to drill offshore at Chicxulub, and 
the first to target its peak ring. "We don't really know what this 
material will look like," says Jaime Urrutia-Fucugauchi, a geophysicist 
at the National Autonomous University of Mexico in Mexico City. "It 
could be a real surprise."

The US$10-million project is funded primarily by the European Consortium 
for Ocean Research Drilling, and involves researchers from Europe, Mexico, 
the United States and elsewhere. The water at the drill site - about 
30 kilometres offshore from the port of Progreso - is too shallow to 
accommodate conventional ocean-drilling vessels, so the project has hired 
LB Myrtle, a "lift boat" that will drop three enormous pillars to 
the sea floor, then jack itself up to form a temporary drilling platform.


Chicxulub is the only impact crater on Earth both big enough and well-preserved 
enough to still have a peak ring. Finding out exactly how the rocks are 
layered in the core will help researchers to evaluate several competing 
models of peak-ring formation, says David Kring, a geologist at the Lunar 
and Planetary Institute in Houston, Texas. He and his colleagues studied 
the peak ring inside the lunar crater Schrodinger to predict what sorts 
of rock might exist in the Chicxulub core4.

Drillers will quickly bore their way through the top 500 metres of sediments, 
and then collect core samples more carefully as they go deeper. "At 
every level you'll get a win," says Sean Gulick, a geophysicist at 
the University of Texas at Austin and the expedition's other co-chief 
scientist. At about 600 metres, the core will pass through rock from the 
Palaeocene-Eocene Thermal Maximum, when temperatures spiked about 55 
million years ago, creating a greenhouse world. At 650 metres the core 
should hit the peak ring.

Primordial ooze

Perhaps the biggest question about the peak ring is where its rocks came 
from. If the rocks within the ring are relatively light in colour, they 
probably came from the topmost 5-10 kilometres of Earth's crust. Darker 
rocks are likely to be rich in elements such as iron and magnesium, and 
probably came from greater depths - perhaps 10-15 kilometres down. 
Confirming the depth of the peak-ring rocks will help modellers to understand 
how the crust fractures and flows during a giant impact.

The core could also reveal whether the impact fostered life even while 
destroying it. When the asteroid shattered Earth's crust, heat and water 
began flowing through the fragmented rocks. Microbes may have thrived 
in that warm, watery habitat, so microbiologists will test the cores for 
ancient DNA and other signatures of living organisms. "By looking directly 
at ground zero, we can watch life recover," says Gulick.

>From the drill rig, the cores will be sent to Bremen, Germany, for more 
detailed study later this year. Urrutia-Fucugauchi hopes that some of 
the most dramatic samples will eventually return to Mexico, perhaps to 
a new core laboratory at the Yucatan Science and Technology Park on the 
outskirts of Merida.

Nature
doi:10.1038/nature.2016.19643