Science shed light on mysteries of evolution, dark matter and the deep ocean
The noughties saw the discovery of key characters in the story of our own evolution, the full catalogue of the human genome and an enhanced understanding of mysterious dark matter.
The biggest physics experiment in the world switched on, broke down, and got up and running once again.
Here, some of the leading scientists at the forefront of the past decade's most significant research tell us what it all really means.
SEARCHING FOR PLANETS
Martin Rees is president of the UK's Royal Society and professor of cosmology at the University of Cambridge. He says what we have learned in the last decade has made the night sky far more interesting:
"Many stars are orbited by retinues of planets - just as the Earth orbits our Sun.
The first "extra-solar" planet was discovered in the 1990s. But in the last few years the pace of research has accelerated, and now more than 400 have been detected.
Up to half of the stars like the Sun may have planets; there are probably many billions of planets in our galaxy.
So far, the detected planets have resembled Jupiter and Saturn, the giants of our own Solar System, rather than the Earth.
But the Kepler spacecraft, launched in March this year, should reveal planets no bigger than our Earth by detecting a slight "shadowing" effect when one of them passes in front of its parent star.
It may be the end of the next decade before we have telescopes powerful enough to directly image Earth-like planets, and reveal whether they have continents and oceans.
The search for planets is restricted to our own Milky Way
If we understood better how life emerged here on Earth - and there is now a real chance of progress on that front - we would be able to lay firmer odds on the likelihood of life elsewhere.
While, by cosmic standards, our study of planets around other stars is parochial, with our gaze is restricted to our own Milky Way, my second highlight is undoubtedly part of the big picture.
Measurements of the faint "afterglow" from the Big Bang, and of very distant galaxies, have greatly firmed up our picture of how our cosmos transformed from a dense and mysterious beginning 13.7 billion years ago into the panorama of stars and galaxies we see around us."
Professor Chris Stringer is the research leader in human origins at London's Natural History Museum. He explains that a remarkable and controversial human-like skeleton was one of the decade's most valuable scientific discoveries:
"A partial human-like skeleton from the Liang Bua Cave on Flores, found alongside stone tools and the remains of an extinct elephant-like creature called Stegodon, is still one of the most challenging finds to science, six years after its discovery.
First, it was found on an island 500km beyond the known range of ancient humans in South East Asia, and second, dating evidence suggests the creature was alive only about 18,000 years ago.
Third, the skeleton displayed a remarkable combination of features - it was adult but only about a metre tall, and its skull indicated a brain size similar to that of a chimpanzee. Because of its small stature the find, which is officially known as Homo floresiensis, acquired the nickname of the "Hobbit".
It had human-like teeth, and its hipbones indicated that it walked upright, but showed some primitive features which hark back to early human and pre-human forms that are 2 million or more years old. So what was this strange creature, which was still alive some 12,000 years after the Neanderthals had gone extinct in Europe?
From the beginning, the find was enveloped in controversy. Some refused to accept that it was anything other than a small modern human, suffering from microcephaly, Laron Syndrome, cretinism, or some other pathology.
But more fragments of skeletons have been found since, with the same unusual features. These ranged in date from about 15,000 down to about 90,000 years.
I am convinced that this is a primitive, rather than a modern, human-like form.
But what it really is, how and when it got to Flores, where it came from, and what led to its extinction, all remain to be determined.
And the fact that this creature with an ape-sized brain was apparently making and using a range of stone tools, and eating the flesh of Stegodon, only adds to the mystery of this extraordinary discovery."
A HUMAN CODE
Dr Tim Hubbard is the head of informatics at the UK's Wellcome Trust Sanger Institute. He played a key role in the Human Genome Project and here he explains just how great an achievement this venture was:
"The draft human genome sequence was announced in June 2000, available to all on the internet. Its determination was profound and a decade of dramatic progress by scientists across the world is built upon it.
Maps of variation between our individual genomes have allowed us to compare genomes of those with a disease to those without and identify many of the genes involved.
The investigation of thousands of patients has opened up new, unexpected directions for research towards medical treatments.
In existing studies just one million points out of the three billion letter human genome are checked. But with the rapidly falling cost of genome sequencing, it is becoming possible to check the whole genome.
We can look forward to medicine in the next decade where, particularly for cancer, sequencing and analysis of an individual's genome becomes part of diagnosis and progress towards personalised treatments.
Analysis of a patient's genome could soon become part of medical diagnosis
The scale of biological data being collected in genome sequencing is vast and comparable to the biggest physics experiments. The challenge now is to make the most of all of this information.
Genome projects have changed scientific culture towards greater data sharing. Fragments of the human genome were made freely available to all within just 24 hours of their generation, to maximise their use by other scientists.
This radical approach enabled rapid progress and has become the norm for biology projects that are on a similar scale."
THE INGREDIENTS FOR LIFE?
Dr Michele Dougherty is professor of space physics at Imperial College London. She led the team that designed the magnetic field instrument aboard the Cassini spacecraft. This experiment was responsible for what she says is one of the most significant discoveries in our Solar System:
"The Cassini spacecraft completed its four-year mission to explore the Saturn system in 2008. It continues to thrive and is now working overtime.
Its most important discovery was that of a dynamic atmosphere at one of Saturn's small moons, Enceladus.
At the dawn of a new decade, this finding is still driving discussions for future missions to Enceladus, to search for life in our Solar System.
Our team's instrument revealed outgassing of water vapour at Enceladus. On a distant flyby of this moon in 2005, perturbations in the magnetic field data led us to conclude that Enceladus had an atmosphere made up of water vapour constituents that were acting as an obstacle to the plasma flow.
Saturn's small, icy moon has a dynamic atmosphere
The implications of these results were so critical that our team convinced the Cassini project to move a follow-on Enceladus flyby - three months later - much closer in to the moon.
This eventually skimmed just 173km above Enceladus' surface, allowing detailed exploration of this potential atmosphere.
The flyby confirmed that a plume filled with water vapour, dust and hydrocarbons was emanating from cracks on the icy south polar surface.
The existence of water and hydrocarbons on this icy moon has made it one of our Solar System's prime candidates in the search for life."
MOST MYSTERIOUS MATTER
Dr Richard Massey is a fellow in astronomy at the Royal Observatory, Edinburgh. He explains why this has been a key decade in the search for the mysterious matter that pervades our Universe:
"This decade has seen the first, dramatic glimpses of dark matter. As the most common stuff in the Universe but in a parallel world of its own, it has long been the elephant in the laboratory.
Billions of dark matter particles whizz through your outstretched hand every second, blithely ignoring it. Only a few dozen ethereal particles might bounce off your hand in a lifetime.
Astronomer Fritz Zwicky noticed in 1933 that most of galaxies' mass is invisible. He suggested it could be mapped via gravitational lensing - the bending of light around anything heavy.
Gravitational lensing has since been measured with the Hubble telescope, revealing invisible tendrils of dark matter around and between every galaxy.
Its unique properties were best demonstrated in 2004, when the periodic table was seen piling up during a galactic car crash - while the dark matter nonchalantly swept through unawares.
Now, a particle accelerator that took the whole decade to build - the Large Hadron Collider (LHC) - is making the fastest ever collisions in a lab. These may create a few particles of dark matter for closer study over the next decade.
But tentative evidence is mounting from other experiments, and the race is on for direct detections. Occasional interactions of dark matter at the centre of our Milky Way may have been seen as a faint glow of microwave light in 2008 and gamma-rays in 2009.
Just this month, reports of two suspected dark matter particles surfaced from the Soudan mine in Minnesota. Tragically, this was announced in the same week as funding cuts leading to the closure of its competitor in the UK."
THE MOTHER OF ALL MACHINES
Alvaro De Rujula is a theoretical physicist at Cern - the European Organization for Nuclear Research - that hosts the Large Hadron Collider (LHC). He says it is on its way to answering fundamental questions about our Universe:
"The LHC and its particle detectors will explore the collisions between two beams of protons, or atomic nuclei, up to energies seven times higher than ever reached in a laboratory on this planet. It is the largest, most complex project ever - the mother of all machines.
After a severe accident in 2008, the LHC has been repaired and it began to function by the end of 2009. It has already produced the highest-energy man-made collisions, and these are still far from what it is capable of.
The technological achievement of having protons accelerated and their collisions neatly recorded, all in a few weeks - following 20 years of work by thousands of scientists and engineers - is enormous.
It is a time of elation and hope for significant steps in our understanding of the fundamental laws of nature.
The bets are on as to whether the LHC will reveal the Higgs boson
The LHC is looking for microscopic space dimensions, for particles of a mysterious dark matter that populate the Universe. It is searching for surprises.
But, above all, it is trying to find "the Higgs".
Physicists argue that a vacuum is not empty. Once you take everything out of a vessel and cool it to absolute zero, you might expect nothing to remain inside.
But the vacuum may still be a substance, permeated by a "Higgs field". Different particles would "feel" this field differently, leading to their different masses. Physicists want to check whether this strange idea is true.
If the vacuum is a substance, one can make it vibrate. The vibrations of a field are particles.
A vibration of the vacuum would be the most-coveted Higgs boson. And the LHC is so powerful, it should be able to shake the vacuum hard enough to make them.
So will the Higgs boson be found? The bets are on and mine is a halfway wager. I think we will find something like it, but not quite what we expected."
Tejinder Virdee, a professor of high energy physics at Imperial College London, who is also based at Cern, says that new technologies had to be invented to complete the LHC:
"The end of the noughties marks the start of the second half of this incredible journey to understand how the Universe works at a deeper level.
The current theory of particle physics, one of the crowning achievements of 20th Century science and underpinning much scientific knowledge, has been experimentally verified to exquisite detail.
But we know that it has many shortcomings at the energies to be probed by the LHC. Currently favoured solutions involve the existence of new phenomena, such as the Higgs mechanism.
Nature may have addressed the shortcomings differently and may well hold surprises, revealing phenomena we have not yet thought of. To find out is why we do experiments. The LHC experiments are designed to discover whatever nature has in store at this special energy."
A CENSUS OF THE SEA
Dr Ron O'Dor, senior scientist at the Census for Marine Life, says that this unprecedented global programme has discovered new habitats as well as new species:
In the 1990s, a panel representing the US National Research Council reported that no nation in the world had a catalogue of the life in its marine economic zone. This was a condition of the Convention on Biological Diversity.
To rectify this, the Alfred P Sloan Foundation agreed to fund a decade-long Census of Marine Life. It evolved into a three-quarter billion dollar programme involving thousands of scientists from 82 countries.
Researchers took samples from the Arctic to the Antarctic, from the seafloor to the surface, near-shore to mid-ocean and microbes to mammals.
This was and continues to be an unprecedented global collaboration.
The census has provided 20 million records records of marine species
A global database now provides over 20 million records of species in the waters of all nations, as well as the deep sea. And beyond this, the census has already discovered some 6,000 new species and new habitats, from boiling fish to giant microbes.
Experimental technologies have become routine observational tools that will allow us to understand the impacts of climate change and human activity on the over 90% of the biosphere that lies beneath the waves.
Census projects have created a transparent ocean where DNA barcodes allow species to be identified in hours instead of months and where the migrations of animals from 20 grams to 20 mega-tonnes can be followed between countries and between oceans.
One record-setting bluefin tuna crossed the Pacific three times, averaging over 100 km per day.
With this incredible dataset, we can now directly monitor endangered species and establish protected areas. This information is vital for conservation and sustainable fisheries.
BIOFUELS - FRIEND OR FOE?
Joyce Tait is a professor at Edinburgh University and chair of the Nuffield Council on Bioethics Working Party on Biofuels. Among the controversy and food price hikes, she says research during the past decade has made it possible to produce a new, improved generation of sustainable fuels:
"Biofuels (derived from microorganisms, plant or animal material) were pioneered in the very early days of car manufacturing - Henry Ford's 1908 Model T engine ran on bioethanol. But cheap fossil fuels soon replaced them.
However, in the last decade increasing concerns about climate change and greenhouse gas emissions have brought them back into the picture.
Scientists hoped biofuels would provide a renewable and sustainable source of energy. However "first generation" biofuels were produced mainly from food crops such as corn, soy bean and wheat.
In most cases their net greenhouse gas emissions were not much better than those of fossil fuels.
A new generation of biofuels is being developed using organisms such as algae
Many also had negative environmental impacts, caused food prices to rise, or caused problems for farmers in developing countries. There were riots in Mexico in 2007 after the price of corn tortillas rose 400% because of the high demand for corn to produce ethanol in the US.
Investment is now being directed at developing improved biofuels using algae, trees, the inedible "woody" parts of plants, and agricultural waste.
We can now use new chemical and biotechnology processes, such as advanced plant breeding, genetic modification and synthetic biology, to improve biofuel production from these new sources.
This could considerably reduce the net CO2 emissions from fuel. But we need to give more consideration this time to how the technology will be developed and what will be the costs and benefits across the whole fuel cycle."