Rethinking the origins of life

Research suggests that comets hitting the Earth - and perhaps other planets in our solar system - could have produced life-building prebiotic compounds

A simulation shows a comet hitting the young Earth, generating the amino acids necessary for life

Scientists have shown a new way in which the building blocks of life could have been created on Earth and elsewhere in the solar system.

They fired ultra-fast projectiles into an icy mixture simulating a comet. The shockwave caused chemical reactions that produced “prebiotic” life-building compounds including amino acids, which make up proteins.

The Anglo-American study, published in Nature Geoscience, suggests that icy comets hitting a rocky planet – or, conversely, rocky meteorites hitting an icy planet – would have produced amino acids in the same way.

“This provides an additional, realistic, synthetic pathway for the building blocks of prebiotic compounds, increasing the chances of life originating and being widespread throughout our solar system,” the paper concludes.

The experiment was designed to test a prediction by Nir Goldman of Lawrence Livermore National Laboratory in California that bombardment of Earth by icy comets around 4bn years ago would have generated prebiotic chemicals through shock-induced reactions.

Goldman enlisted the help of UK colleagues at the University of Kent and Imperial College London, who had access to a “gas gun” built for hypervelocity smashes. They made ice containing ammonia, methanol and carbon dioxide – mimicking the composition of a comet – and fired steel projectiles into it at 7.15km per second. Chemical analysis confirmed that the impacts did indeed generate amino acids.

The surfaces of Saturn’s moon Enceladus and Jupiter’s moon Europa, covered with similar ice, would be good environments for amino acids to form, the scientists say. This conclusion should encourage space agencies to plan missions to search for signs of simple life there.

“Our study widens the scope for where these building blocks may be formed in the solar system and adds another piece to the puzzle of how life on our planet took root,” says Zita Martins of Imperial College.

As far as life on Earth is concerned, cometary impact provides an alternative mechanism for generating prebiotic building blocks to the one demonstrated 60 years ago at the University of Chicago: Stanley Miller and Harold Urey simulated the effects of lightning strikes in an atmosphere containing water, methane, hydrogen and ammonia – like that of the young Earth – and obtained several amino acids.

While both the 1953 Chicago experiment and the 2013 comet impact simulation provide building blocks for life, neither explains how nature linked these together into proteins – or how self-replicating systems came to encode genetic information through RNA and DNA. The big questions about the origins of life remain unanswered.

The brains behind boom and bust

Research into the neural processes underpinning financial decisions – and the psychology of market bubbles and their collapse – has gathered pace since the banking crisis five years ago.

The latest study, carried out at the California Institute of Technology and published in the journal Neuron, looked at the neural activity of student volunteers as they bought and sold shares in a staged financial market. To make the game realistic, the students could keep any money they made (as much as $300).

When researchers mapped participants’ brain activity, they found that the formation of bubbles – when trading pushes the price of an asset well above its intrinsic value – was linked to increased activity in a brain area called the ventromedial prefrontal cortex (vmPFC), which processes value judgments. Individuals with more activity here were more likely to lose money by paying inflated prices for assets.

The study also showed a correlation between activity in this part of the brain and the dorsomedial prefrontal cortex (dmPFC), which processes social signals to discern people’s intentions and predict behaviour.

Benedetto De Martino, the project leader, says the results show that a bubble arises when people shift mental processes when making financial decisions. They become less focused on prices and values, and more on imagining how other traders will behave.

“These processes have evolved to help us get along better in social situations,” he says. “But we’ve shown that when we use them within a complex modern system, like financial markets, unproductive behaviours that drive a cycle of boom and bust can result.”

The researchers say the study could help to design better social and financial interventions in order to reduce the risk of market bubbles.

The secrets of metastasis unfold

Invasive tumour cells in a mouse

Peter Friedl and his team have sewn a cancerous tumour into a sleeping mouse. For the next few weeks they will watch it grow with the aid of a high-powered microscope, writes Aaron Hagstrom.

Friedl holds up a fluorescent multicoloured image showing a greenish fuzz of cells lying on its periphery. “That’s the tumour after one day,” he says. Another image shows aggressive greenish finger-like strands reaching deep into healthy brown tissue.

“After a couple of weeks, it is like the mafia infiltrating the police,” Friedl says. “We have found that tumours grow in the body much like plants taking root in the soil – by sending out tentacles of cells deep into the tissue.”

Metastasis, which is responsible for about 90 per cent of cancer deaths, was once poorly understood because microscopes did not offer sufficient magnification and resolution to observe tumour cells in living animals. Their lasers damaged the tissue after a brief period of observation. As a result, research was confined to observing cells in test tubes and Petri dishes.

But Friedl and his team are finally teasing out the secrets of metastasis at the University Medical Centre in Nijmegen in the Netherlands, where he directs the Microscopic Imaging Centre and a research group that focuses on the imaging of cell dynamics.

His expertise in infrared multi-photon microscopy has been key to the centre’s understanding of cancer. The microscope generates 3D representations of living tissue by exciting fluorescence with low-energy photons.

In research conducted over five years, Friedl discovered that this technology is ideal for observing cell dynamics deeper inside tumours, at higher resolutions and over longer periods of time.

“It sounds like nothing but it is as good as going to the moon,” he said. “It isn’t yet outside of our solar system but it has furthered our understanding of tumour dynamics.”

With these breakthroughs, he understands better how cancer cells collectively propagate. He found they use tissue structures – vessels, muscles and nerves – as highways. This contradicted a previous assumption that cancer cells destroyed everything in their path. In his most recent discovery this summer, Friedl found the exact conditions by which cell motion is restricted or facilitated within connective tissue.

Despite these successes, his laboratory and others have been unsuccessful in finding drugs to inhibit tumour cell propagation. Friedl says this is because cancer cells behave much like magicians. Their behaviour is unpredictable with current knowledge; so much depends on the individual characteristics of the cancer and patient.

“In the end, if you challenge them just hard enough, tumour cells can do everything,” he said. “It is a little bit of the cat-and-mouse game. We chop off one pathway and the cells pop out somewhere else.”

Even so Friedl hopes to develop novel treatments for cancer, through flexible combinations of chemotherapy, radiation and other therapies.

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