What on Earth?

Four billion years ago, when the Earth was but a mere babe nestled in the cradle of the solar accretion disc, the local environs were littered with asteroid-sized chunks of rock known as planetesimals. The Period of Heavy Bombardment, which lasted from about 4.5 to 3.8 billion years ago, saw the planetesimals colliding with the Earth on a daily basis. Not the gentlest of starts to life.

In October, delegates at Perspectives in Astrobiology, a NATO Advanced Studies Institute in Chania, Crete, heard how there is something anomalous about the end of the Period of Heavy Bombardment. We know from the fossil record that life has existed on Earth since around 3.8 billion years ago but how could it have survived and indeed thrived during the daily onslaught of the PHB?

Could the Moon harbour the secrets of life on Earth? (Credit: NASA)

Could the Moon harbour the secrets of life on Earth? (Credit: NASA)

Some astrobiologists believe those bombarding chunks of rock, or perhaps a comet, may have carried the seeds of life to Earth, explaining its origins during the PHB. Others wonder whether the rocky colliders simply deposited the raw materials, organic building blocks, ready for Earth’s seemingly special conditions to trigger the emergence of life. There is no clear answer yet.

Astrobiologists, however, think they now have a source of rock from that epoch that is truly out of this world and could allow them to study the molecular fossils from the dawn of time as well as revealing much about the wind and rain, earthquakes and plate tectonics on Earth at that time.

John Armstrong

John Armstrong

But, where is this ancient record of Earth’s early days?

Guillermo Gonzalez

Guillermo Gonzalez

According to John Armstrong and Llyd Wells of the University of Washington and Guillermo Gonzalez at Iowa State University it is on the Moon.

A large Moon rock nicknamed Big Muley, weighing 11.7 kg. This rock was the largest returned to Earth by Apollo astronauts. (Credit: NASA)

A large Moon rock nicknamed Big Muley, weighing 11.7 kg. This rock was the largest returned to Earth by Apollo astronauts. (Credit: NASA)

All those repeated collisions had quite an impact on the Earth, flinging off great pieces of debris into space. 4.5 billion years ago, astronomers believe, the Moon itself was simply another piece of space debris, the original chip off the old block, trapped in Earth’s orbit after a particularly violent collision between Earth and a Mars-sized planetesimal. During the PHB plenty more debris was hewn from the Earth and would have been cleaned up by the Moon when it was much closer to the Earth than it is today, as it orbited the young Earth.

The lack of weather and plate tectonics on the Moon mean, much of that debris might still be lying still on the Moon’s surface. The researchers suggest that at least 20 tonnes of Earth material might cover every 100 square kilometre of the Moon’s surface. The Apollo missions brought back to Earth a mere fraction of the Moon’s surface rocks and soils, some 400 kg. Could there be some non-Lunar material in those samples? Armstrong reckons it is a possibility and that samples from the Moon’s eastern limb, as seen from Earth might be the place to look, because that would have likely gathered up the most debris from Earth’s orbit.

Spotting the chemical differences between true Moon rock and more recently acquired Earth debris on the Moon’s surface will be key to determining the original origin of a sample. The presence of hydrated minerals or hydrocarbons would be the first characteristics to investigate.

Further reading

John Armstrong
http://space.weber.edu/~jca/HomePage/John_Armstrong.html

Guillermo Gonzalez
http://www.public.iastate.edu/~astro/faculty/gonzalez.html

Suggested searches

Astrobiology
Lunar surface
Moon formation
Moon

Weathering volcanoes

Accurate weather forecasts could help predict volcanic eruptions, according to British environmental scientists.

Researchers at the University of East Anglia working with colleagues at the Montserrat Volcano Observatory and the University of Maryland have discovered that intense rainfall can trigger volcanic dome collapse. This leads to a particular type of eruption in which a build-up of molten rock inside the side of the volcano becomes unstable and collapses spewing out lava, toxic gases, and rock.

The Soufrière Hills volcano in Montserrat with pyroclastic flow deposits visible on the left flank

The Soufrière Hills volcano in Montserrat with pyroclastic flow deposits visible on the left flank

The eruption on the Caribbean island of Montserrat in July last year coincided with the first heavy rainfall in seven months, explains team member Adrian Matthews. Within hours of the rainfall starting the volcanic dome collapsed. Matthews, a meteorologist, leads the research team with UEA volcanologist, Jenni Barclay. The scientists also found that two previous eruptions of the Montserrat volcano, Soufriere Hills, had also been preceded by heavy rainfall.

The researchers point out that one of the most dangerous aspects of volcanic dome collapse is the accompanying surge of searing hot rocks and boulders that are carried at high speed down the mountain on a bed of volcanic gases, the pyroclastic flow. Weather forecasts, the team says, used in conjunction with rainfall records might help make more accurate predictions of imminent volcanic activity and offer people who live in the shadow of active volcanoes an early warning of eruptions.

The devastated Montserrat capital of Plymouth under volcanic debris

The devastated Montserrat capital of Plymouth under volcanic debris

Montserrat had seven months with little rain and a period of sustained volcanic dome growth. Once the intense rain set in, it was only a matter of hours before the dome collapsed and pyroclastic flows started. The weather system that brought the rain could be seen in satellite images and was forecast 60 hours before the volcanic activity. The next step is to work out how the rainfall triggers the eruption, it may be the water being turned to steam and building up inside the dome, like a pressure cooker, adds Matthews.

Further reading

Geophys. Res. Lett., 29(13) (2002)
http://dx.doi.org/10.1029/2002GL014863

Soufriere Hills
http://www.geo.mtu.edu/volcanoes/west.indies/soufriere/

Suggested searches

Soufriere Hills volcano
Pyroclastic flows
Volcanoes

DNA and chips

The secret ingredient in a future biological computer is to add a little DNA. But, making hybrid devices from a silicon chip and a strand of genetic material means mixing hard-wired microelectronics technology with the softer world of molecular biology.

Now, chemists at the University of Newcastle upon Tyne have come up with a solution that could lead to new lab-on-a-chip devices and biological sensors for use in medicine and environmental analysis. It might even one day allow biology to compute or provide an interface between electronic devices and living things.

Ben Horrocks

Ben Horrocks

Newcastle chemists Benjamin Horrocks and Andrew Houlton and their colleagues have devised a way to automate the solid-phase synthesis of DNA on a semiconductor chip. They believe their method could readily be adapted to the conventional fabrication techniques of photolithography used in the microelectronics industry to pattern the microscopic transistors and circuitry on a computer chip.

The team recently reported how it has found a way to attach a DNA sequence of just seventeen nucleotides to a silicon surface modified with organic molecules. The key to unlocking hybrid DNA chips lies in the team’s use of bifunctional organic molecules. At one end the molecule has the right chemistry to allow it to be attached to an oxide-free silicon surface. The other end of the molecule has a functional chemical group on which a DNA strand can be grown using an automated DNA synthesizer of the kind found in biotech laboratories the world over.

Andrew Houlton

Andrew Houlton

The team is working with two aims in mind – first, the development of chemical sensors and secondly the synthesis of DNA on silicon surfaces for nanoscale molecular architecture. This addresses the projected reduction in the size of electronic components which by 2015 are predicted to be of the order of nanometres (i.e. built from molecules), explains Houlton.

Gel electrophoresis reveals DNA is attached to the silicon

Gel electrophoresis reveals DNA is attached to the silicon

Previous endeavours in this area have generally used glass in preference to silicon wafers and those that have focused on silicon have applied organic molecules to an oxidised surface rather than the naked silicon chip. The Newcastle team has now confirmed that it is possible to cover the surface of a silicon chip with DNA strands. Moreover, the 17-base DNA strands can be coupled with the complementary DNA strand making the familiar DNA double helix. From the nanodevice perspective the importance of the team’s work lies in their ability to pattern the surface of the silicon rather than simply randomly deposit DNA strands. Patterning using the printing and etching techniques of microelectronics fabrication means they can tightly control the arrangement of the DNA on the surface and so produce what might one day become molecular circuitry.

A DNA-patterned silicon surface

A DNA-patterned silicon surface

Sequential modification of a silicon surface with DNA

Sequential modification of a silicon surface with DNA

Further reading

Angew. Chem. Int. Ed., 41, 615 (2002)
http://www3.interscience.wiley.com/cgi-bin/abstract/90512278/ABSTRACT

DOI: 10.1002/1521-3773(20020215)41:4<615::AID-ANIE615>3.0.CO;2-Y

Benjamin Horrocks
http://www.ncl.ac.uk/chemistry/staff/profile/b.r.horrocks

Andrew Houlton
http://www.ncl.ac.uk/chemistry/staff/profile/andrew.houlton

Suggested searches

Molecular Electronics
Nanotechnology