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

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 31 Mar 2016 16:41:06 -0700 (PDT)
Message-ID: <201603312341.u2VNf6P7027960_at_zagami.jpl.nasa.gov>


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.

Received on Thu 31 Mar 2016 07:41:06 PM PDT

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