Constructing the Earth
“I tell my wife that her fresh glass of water isn’t so fresh. It has atoms in it that are 14 billion years old.”
Andy McWilliam
of the Observatories was the first speaker. His talk, “Stars and
the Formation of the Elements,” emphasized the fact that all of us—and
all of life—contain products from the nuclear physics of massive
stars that went supernova—the spectacular explosions that eject the
elements found in the universe today. McWilliam provided an overview of
the process of element recycling and synthesis that started with the Big
Bang. The lightest elements—hydrogen, helium, lithium, beryllium,
and boron—were produced by that event. Heavier elements such as silicon
and carbon, which are the grist for planets and for life, came later via
nuclear processing inside massive stars. McWilliam made it clear how important
stars are to the creation of life when he said that the iron and calcium
atoms in our bodies come from one million to tens of millions of supernova
events.
(Courtesy European Southern Observatory and the Space Telescope Science Institute.)
Sleuthing solar systems through dust
Alycia Weinberger,
the newest member of the DTM research staff, looks for analogs to our early
solar system by exploring the dusty disks surrounding young stars similar
to our early Sun. She began her talk, “Young Stellar Disks as the Sites
of Planetary Evolution,” with a summary of the planetary formation
process—from a collapsing protostar all the way to the construction
of terrestrial planets. Young disks have lots of dust and gas encompassing
and obscuring the central star. Fortunately, these particle shrouds radiate
in the infrared (IR). Weinberger and colleagues image disks in the IR and
pay particular attention to the structure they exhibit. The way a disk is
sculpted can provide clues to the presence of planets. Weinberger used Beta
Pictoris as one of her examples. She showed that the inner disk surrounding
the star is warped, and suggested that this may have resulted from perturbations
exerted by an orbiting object. In addition to analyzing disk structure,
Weinberger looks at the chemistry of these disks at varying distances from
the central star. This spectral analysis can reveal a lot. It tells researchers
how materials are formed and distributed during early planet formation,
and therefore how they came to be incorporated into young planets. (Courtesy Alycia Weinberger.)
“Forty thousand tons of extraterrestrial material fall on Earth each year.”
And this cosmic debris provides scientists, such as Conel Alexander of DTM, with a bounty of information about galactic and solar system formation and perhaps the origin of life. Alexander’s talk, “Materials for Solar System Formation,” focused on chondritic meteorites—the oldest and most abundant type of meteorites—and what they can tell us about early solar system evolution. Alexander began his presentation with a chondritic anatomy lesson, pointing out the constituents of the rocks that tell us about solar system formation, and of those that tell us about galactic evolution and the interstellar medium. He also talked about the role meteorites may have had in the origin of life. Analysis has shown that they contain more than 70 amino acids and three of the nucleic acids in RNA and DNA. Many amino acids are so-called chiral molecules, meaning that they come in two mirror-image forms, designated left- and right-handed. It is the left-handed forms that are almost exclusively present in living organisms and that are, in some instances, slightly more abundant in meteorites. With these objects constantly bombarding Earth, they may have ferried the precursors of life here. Alexander observed that “if they played a role in life in our solar system, then maybe they play a role in life elsewhere.”“The lead story on the evening news was that Hekla would erupt in 20 minutes.”
Alan Linde’s
talk, “Volcanic Activity,” reflected how his work at DTM has shifted
over the years from earthquakes to volcanoes. He provided a context for
his presentation by reviewing Earth’s plate tectonics and the worldwide
distribution of earthquakes and volcanoes. He then described a device, called
a strainmeter, developed years ago at DTM by Selwyn Sacks and colleagues
to study earthquakes. Compared with displacement measuring techniques, such
as GPS, strainmeters are able to detect smaller movements, perhaps as deep
as 30 km below the surface. They have been installed in Iceland, Japan,
California, and elsewhere. Linde provided vivid examples of how strainmeters
work and what they can tell us about the interior by using examples of two
active volcanoes—Oshima, in Japan, and Hekla, in Iceland. His Icelandic
example compared an eruption in 1991 with one in 2000. The plots were remarkably
similar, as the volcano went through virtually the same paces the second
time around. This information allowed Linde’s Icelandic collaborator
to issue a warning to the area population just minutes before the volcano
blew and just in time for the evening news. As Linde concluded, “Finding
out how the physics of volcanoes work has a nice by-product—an early-warning
system.” (Courtesy Alan Linde.)
