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Impact
glass from asteroids and comets stores biodata for millions of years
Impact
glass from asteroids and comets stores biodata for millions of years
Date:
April 18,
2014
Source:
Brown University
Summary:
Bits of plant life encapsulated in molten glass by
asteroid and comet impacts millions of years ago give geologists information
about climate and life forms on the ancient Earth. Scientists exploring large
fields of impact glass in Argentina suggest that what happened on Earth might
well have happened on Mars millions of years ago. Martian impact glass could
hold traces of organic compounds.
,......................................
Bits of plant life encapsulated in molten glass by asteroid
and comet impacts millions of years ago give geologists information about
climate and life forms on the ancient Earth. Scientists exploring large fields
of impact glass in Argentina suggest that what happened on Earth might well
have happened on Mars millions of years ago. Martian impact glass could hold
traces of organic compounds
Asteroid and
comet impacts can cause widespread ecological havoc, killing off plants and
animals on regional or even global scales. But new research from Brown
University shows that impacts can also preserve the signatures of ancient life
at the time of an impact.
A research
team led by Brown geologist Pete Schultz has found fragments of leaves and
preserved organic compounds lodged inside glass created by a several ancient
impacts in Argentina. The material could provide a snapshot of environmental
conditions at the time of those impacts. The find also suggests that impact
glasses could be a good place to look for signs of ancient life on Mars.
The work is
published in the latest issue of Geology Magazine.
The
scorching heat produced by asteroid or comet impacts can melt tons of soil and
rock, some of which forms glass as it cools. The soil of eastern Argentina,
south of Buenos Aires, is rife with impact glass created by at least seven
different impacts that occurred between 6,000 and 9 million years ago,
according to Schultz. One of those impacts, dated to around 3 million years
ago, coincides with the disappearance of 35 animal genera, as reported in the
journal Science a few years back.
"We
know these were major impacts because of how far the glass is distributed and
how big the chunks are," Schultz said. "These glasses are present in
different layers of sediment throughout an area about the size of Texas."
Within glass
associated with two of those impacts -- one from 3 million years ago and one
from 9 million years ago -- Schultz and his colleagues found exquisitely preserved
plant matter. "These glasses preserve plant morphology from macro features
all the way down to the micron scale," Schultz said. "It's really
remarkable."
The glass
samples contain centimeter-size leaf fragments, including intact structures
like papillae, tiny bumps that line leaf surfaces. Bundles of vein-like
structures found in several samples are very similar to modern pampas grass, a
species common to that region of Argentina.
Chemical
analysis of the samples also revealed the presence of organic hydrocarbons, the
chemical signatures of living matter.
To
understand how these structures and compounds could have been preserved,
Schultz and his colleagues tried to replicate that preservation in the lab.
They mixed pulverized impact glass with fragments of pampas grass leaves and
heated the mixture at various temperatures for various amounts of time. The
experiments showed that plant material was preserved when the samples were
quickly heated to above 1,500 degrees Celsius.
It appears,
Schultz says, that water in the exterior layers of the leaves insulates the
inside layers, allowing them to stay intact. "The outside of the leaves
takes it for the interior," he said. "It's a little like deep frying.
The outside fries up quickly but the inside takes much longer to cook."
Implications
for Mars
If impact
glass can preserve the signatures of life on Earth, it stands to reason that it
could do the same on Mars, Schultz says. And the soil conditions in Argentina
that contributed to the preservation of samples in this study are not unlike
soils found on Mars.
The Pampas
region of Argentina is covered with thick layers of windblown sediment called
loess. Schultz believes that when an object impacts this sediment, globs of
melted material roll out from the edge of the impact area like molten
snowballs. As they roll, they collect material from the ground and cool quickly
-- the dynamics that the lab experiments showed were important for
preservation. After the impact, those glasses are slowly covered over as dust continues
to accumulate. That helps to preserve both the glasses and the stowaways within
them for long periods -- in the Argentine case, for millions of years.
Much of the
surface of Mars is covered in a loess-like dust, and the same mechanism that
preserved the Argentine samples could also work on Mars.
"Impact
glass may be where the 4 billion-year-old signs of life are hiding,"
Schultz said. "On Mars they're probably not going to come out screaming in
the form of a plant, but we may find traces of organic compounds, which would
be really exciting."
Story
Source:
The above
story is based on materials
provided by Brown University.
Note: Materials may be edited for content and length.
Journal
Reference:
- P. H. Schultz, R. S. Harris, S. J. Clemett, K. L. Thomas-Keprta, M. Zarate. Preserved flora and organics in impact melt breccias. Geology, 2014; DOI: 10.1130/G35343.1
Cite This
Page:
Brown University. "Impact glass
from asteroids and comets stores biodata for millions of years."
ScienceDaily. ScienceDaily, 18 April 2014.
<www.sciencedaily.com/releases/2014/04/140418141115.htm>.
