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Homepage / Science / Earth and the Environment / How Plate Tectonics Got Kick-Started
How Plate Tectonics Got Kick-Started
Scientists propose a new model to explain how plate tectonics, the geological phenomenon behind earthquakes and volcanoes, got started.
By Joshua A. Krisch
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September 17, 2014 1:00 PM Text Size: A . A . A
The outermost shell of the Earth is constantly in motion. Over eons, our planet’s tectonic plates have dragged the continents apart and slammed them into one another, forming ocean trenches, mountains, and volcanoes.
Plate tectonics explains continental drift, seafloor spreading, and why California has so many earthquakes. The Earth’s shifting plates also created an ideal environment for life itself to evolve and thrive. But exactly how our planet’s seven or eight major plates started shifting remains a mystery. Today, in a study published in Nature, researchers model the conditions that may have kick-started plate tectonics billions of years ago.
“Over the past decade, we have kept with the idea that plate tectonics was not something that was born with our planet,” says Patrice Rey, a geoscientist at the University of Sydney in Australia and lead author on the study. “The Earth started with a stagnant plate. The question was, how do we move from there to a situation where we have plate tectonics?”
A Hotter, Heavier Earth
Modern geological plates move about in a predictable fashion. The top portion of a plate is relatively cooler and denser than the Earth below it, and this state of “negative buoyancy” causes one plate to slip, or subduct, under another. But scientists have long suspected that during the Archaean Eon, 2.5 billion years ago, geological plates were more static.
“We look at these old Archaean crusts, for instance, and we don’t see the features that characterize subduction,” Rey says.
This implies that some geological event must have initially set the plates in motion. Rey and his colleagues suspected that early Earth’s unique geology might have had something to do with it. Hundreds of millions of years ago, Earth’s interior was hotter and its crust was thicker. Rey wondered whether heavier continents might have pushed against nearby plates, initiating subduction.
“Continents have a natural tendency to spread horizontally and push other plates on their sides,” Rey says. “When we put this physics into a computer model, we realized that it had the power to force the plate into subduction.”
In the movie a continent (made of a depleted lithospheric mantle in green and continental crust in red) is slowly spreading toward the adjacent oceanic lithosphere (blue). A short-lived subduction zone develops following 45 myr of slow spreading. This subduction episode allows the continent to surge toward the ocean, leading to its “boudinage” and allowing the detachment of a continental block. This movie shows an 87 myr long story. (Credit: Patrice F Rey, Nicolas Coltice and Nicolas Flament)
New Models for Ancient Problems
The study presents a compelling story about how plate tectonics began. Continents grew denser, sank, and ultimately shoved their compatriots out of the way. Over time, these shoving matches developed into a familiar, self-sustaining cycle of subduction.
For some experts, though the most exciting aspect of the study is that Rey and his team found a way to use modern techniques to answer very old problems.
“What jumped out was that they could apply the modern tools of mechanical modeling to a problem that really pre-dates plate tectonics,” says Larry Brown, a geophysicist at Cornell University who was not involved in the research. “It’s tying it all together, with a nice dash of physical quantitativeness.”
Nourishing Life with Rocks
There’s also a curious link between the onset of plate tectonics and the evolution of biology. By moving landmasses apart and forming mountains and valleys, plate tectonics effectively gave rise to a number of unique ecosystems where new life forms could flourish.
“If you want to have very vibrant viable biosphere with a lot of species, what you need is to provide lots of different ecosystems,” Rey says. “There’s a link between initiation of plate tectonics on Earth and the development of a strong and vibrant biosphere.”
Rey and his colleagues are now preparing a more complete model, based on their initial findings, that would show how the continents themselves came to be. “What our model doesn’t cover is the formation of continents,” Rey says. “We’re working actively on that at the moment to bring that story into our model.”
Tags: plate tectonics, earthquakes, geology, volcanoes
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Posted: 16 Sep 2014 12:27 PM PDT How the media shafted the people of Scotland.
By George Monbiot, published in the Guardian 17th September 2014 Perhaps the most arresting fact about the Scottish referendum is this: that there is no newspaper – local, regional or national, English or Scottish – which supports independence except the Sunday Herald. The Scots who will vote yes have been almost without representation in the media. There is nothing unusual about this. Change in any direction except further over the brink of market fundamentalism and planetary destruction requires the defiance of almost the entire battery of salaried opinion. What distinguishes the independence campaign is that it has continued to prosper despite this assault. In the coverage of the referendum we see most of the pathologies of the corporate media. Here, for example, you will find the unfounded generalisations with which less enlightened souls are characterised. In the Spectator, Simon Heffer mainatains that “addicted to welfare … Scots embraced the something for nothing society”, objecting to the poll tax “because many of them felt that paying taxes ought to be the responsibility of someone else.”(1) Here is the condescension with which the dominant classes have always treated those they regard as inferior: their serfs, the poor, the Irish, Africans, anyone with whom they disagree. “What spoilt, selfish, childlike fools those Scots are … They simply don’t have a clue how lucky they are,” sneered Melanie Reid in the Times(2). Here is the chronic inability to distinguish between a cause and a person: the referendum is widely portrayed as a vote about Alex Salmond, who is then monstered beyond recognition (a Telegraph leader last week compared him to Robert Mugabe(3)). The problem with the media is exemplified by Dominic Lawson’s column for the Daily Mail last week(4). He began with Scotland, comparing the “threat” of independence with the threat presented by Hitler (the article was helpfully illustrated with a picture of the Fuhrer, unaccompanied in this case by the Mail’s former proprietor). Then he turned to the momentous issue of how he almost said something wrong about David Attenborough, which was narrowly averted because “as it happens, last weekend we had staying with us another of the BBC’s great figures, its world affairs editor John Simpson”, who happily corrected Lawson’s mistake. This was just as well because “the next day I went to the Royal Albert Hall as one of a small number of guests invited by the Proms director for that night’s performance. And who should I see as soon as I entered the little room set aside for our group’s pre-concert drinks? Sir David Attenborough.” Those who are supposed to hold power to account live in a rarified, self-referential world of power, circulating among people as exalted as themselves, the “small number of guests” who receive the most charming invitations. That a senior journalist at the BBC should be the house guest of a columnist for the Daily Mail surprises me not one iota. In June the BBC’s economics editor Robert Peston complained that BBC news “is completely obsessed by the agenda set by newspapers … If we think the Mail and Telegraph will lead with this, we should. It’s part of the culture.”(5) This might help to explain why the BBC has attracted so many complaints of bias in favour of the No campaign(6,7). Living within their tiny circle of light, most senior journalists seem unable to comprehend a desire for change. If they notice it at all, they perceive it as a mortal threat: comparable perhaps to Hitler. They know as little of the lives of the 64 million inhabiting the outer darkness as they do of the Andaman islanders. Yet, lecturing the poor from under the wisteria, they claim to speak for the nation. As John Harris reports in the Guardian, both north and south of the border “politics as usual suddenly seems so lost as to look completely absurd.”(8) But to those within the circle, politics still begins and ends in Westminster. The opinions of no one beyond the gilded thousand with whom they associate are worthy of notice. Throughout the years I’ve spent working with protest movements and trying to bring neglected issues to light, one consistent theme has emerged: with a few notable exceptions, journalists are always among the last to twig that things have changed. It’s no wonder that the Scottish opinion polls took them by surprise. One of the roles of the Guardian, which has no proprietor, is to represent the unrepresented – and it often does so to great effect. On Scottish independence I believe we have fallen short. Our leader on Saturday used the frames constructed by the rest of the press, inflating a couple of incidents into a “habit” by yes campaigners of “attacking the messenger and ignoring the message”, judging the long-term future of the nation by current SNP policy, confusing self-determination with nationalism(9). If Westminster is locked into a paralysing neoliberal consensus it is partly because the corporate media, owned and staffed by its beneficiaries, demands it. Any party that challenges this worldview is ruthlessly disciplined. Any party that more noisily promotes corporate power is lauded and championed. UKIP, though it claims to be kicking against the establishment, owes much of its success to the corporate press. For a moment, Rupert Murdoch appeared ready to offer one of his Faustian bargains to the Scottish National Party: my papers for your soul(10). That offer now seems to have been withdrawn, as he has decided that Salmond’s SNP is “not talking about independence, but more welfarism, expensive greenery, etc and passing sovereignty to Brussels”(11) and that it “must change course to prosper if he wins.”(12) It’s not an observation, it’s a warning: if you win independence and pursue this agenda, my newspapers will destroy you. Despite the rise of the social media, the established media continues to define the scope of representative politics in Britain, to shape political demands and to punish and erase those who resist. It is one chamber of the corrupt heart of Britain, pumping fear, misinformation and hatred around the body politic. That so many Scots, lambasted from all quarters as fools, frauds and ingrates, have refused to be bullied is itself a political triumph. If they vote for independence, they will do so in defiance not only of the Westminster consensus, but also of its enforcers: the detached, complacent people who claim to speak on their behalf. References: 1. http://www.spectator.co.uk/australia/australia-features/9226741/little-scotlanders/ 2. http://www.thetimes.co.uk/tto/opinion/columnists/article4200523.ece 6. https://www.opendemocracy.net/ourkingdom/john-robertson/bbc-bias-and-scots-referendum-new-report 7. http://www.bbc.co.uk/news/uk-scotland-29196912 9. http://www.theguardian.com/commentisfree/2014/sep/12/guardian-view-scottish-independence 11. https://twitter.com/rupertmurdoch/status/511187972453314560 12. https://twitter.com/rupertmurdoch/status/511095777440313345 |
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“I Do Like to Be Beside the Seaside” holds true for many Australians who live on or near the coast. On top of the many lifestyle amenities coastal living offers, much of the country’s crucial infrastructure (such as road and rail networks, hospitals, water treatment works and waste disposal facilities) is located along our coastline.
Virtually all of this infrastructure has been designed and built for a stable climate, yet we are living in a new climate system that is no longer stable.
Rising sea levels pose huge financial, economic and humanitarian risks, as shown by the Climate Council’s latest report, Counting the Costs: Climate Change and Coastal Flooding. If the world ignores the problem, by mid-century rising seas could cost the world more than a trillion dollars a year as floods and storm surges hit.
How much will the seas rise?
Climate change is warming the oceans and increasing the flow of ice from the land into the sea. This drives up sea levels, causing coastlines to recede and making flooding more widespread. The primary cause of the 17cm global average sea-level rise observed during the second half of the 20th century is the increase in greenhouse gases in the atmosphere from human activities. And sea level is likely to increase by 0.4-1.0 m through the 21st century.
Strong action to reduce greenhouse gas emissions would keep sea-level rise towards the lower end of that range, while a business-as-usual approach to burning fossil fuels would drive it towards the upper end of the range – with potentially massive economic consequences.
Coastal flooding and economic damage
Coastal flooding has caused, and is projected to cause, severe damage to economies without adaptation and drastic mitigation measures. Hurricane Katrina, which hit the southern United States in 2005, caused $US100 billion ($110 billion) in damage and about 2,000 deaths.
Seven years later, Hurricane Sandy caused $US19 billion in damage to public and private infrastructure and property in New York City alone, as well as hitting other locations along the US east coast and in the Caribbean.
Forget about the Tom Cruise movie Risky Business – the recent report of the same name, Risky Business: the Economic Risks of Climate Change, led by former New York Mayor Michael Bloomberg, is much more apt. It starkly sets out the economic risks of climate change to the United States, including the threat of damage to coastal property and infrastructure from rising sea levels and increased storm surges.
The report predicts that in just over a decade, this double whammy of higher sea levels and storm surges will more than double the costs of coastal storms along the US eastern seaboard and the Gulf of Mexico, to $US3.5 billion a year. Hurricanes Katrina and Sandy are harbingers of things to come.
If the threat of a climate-driven increase in sea level goes unabated, the projected increases in economic damage will be significant. According to a 2011 federal government assessment, more than $226 billion (in 2008 dollars) in commercial, industrial, road and rail, and residential assets around Australia’s coasts are potentially exposed to flooding and erosion hazards if seas were to rise by 1.1m (high-end scenario for 2100).
In southeast Queensland, without adaptation, a current 1-in-100-year coastal flooding event would probably cause about $1.1 billion in damage to residential buildings. With a 0.2m rise in sea level, a similar flooding event would increase the damages to around $2 billion, and a 0.5m rise in sea level would raise projected damages to $3.9 billion.
By 2050, if the threat of sea level rise is ignored, the worldwide losses from coastal flooding (and land subsidence) are projected to hit $US1 trillion per year – roughly the size of the entire Australian economy.
Putting the squeeze on natural ecosystems
Many coastal and near-shore marine ecosystems, such as mangroves, saltmarshes and seagrass beds, may become trapped in a “coastal squeeze” as rising sea levels come up against fixed landward barriers such as seawalls and urban infrastructure.
Damaging these ecosystems has detrimental flow-on effects to water quality, carbon storage, and fisheries. Sea-level rise is increasing the salinity of coastal groundwater and pushing salty water further upstream in estuaries, affecting the health of salt-sensitive plants and animals. Saltwater intrusion from rising sea levels is contributing to the loss of freshwater habitats in coastal regions such as Kakadu National Park. Meanwhile, some corals may not be able to keep up with periods of rapid sea-level rise, which would cause reefs to “drown”.
Australia’s beautiful sandy beaches – a major attraction for Australia’s multi-billion dollar tourism industry – are at risk from coastal erosion. And it’s not just the tourism dollar that is being eroded.
Vulnerable communities
Rising sea level is eroding the viability of coastal communities on Pacific Islands and in low-lying areas of Asia, increasing the likelihood that people will need to resettle elsewhere. Several Torres Strait Island communities live in extremely low-lying areas and already experience flooding during annual high tides. Building seawalls and raising houses can buy time, but in the long term several of these communities may face relocation.
A sea-level rise of 0.5-2.0m could displace between 1.2 million and 2.2 million people from the Caribbean region and the Indian and Pacific Ocean islands, assuming that no adaptation occurs.
The impacts of climate change and coastal flooding are potentially huge. Rapid and deep cuts in greenhouse gas emissions are crucial, both in Australia and around the world, if we are to stabilise the climate and slow the seas’ rise.
If we don’t manage it, then being beside the seaside might turn out not to be so enjoyable after all.
Martin Rice is research manager for the Climate Council and an honorary associate of the Department of Environment and Geography, Macquarie University. John Hunter is an oceanographer at the Antarctic Climate and Ecosystems Cooperative Research Centre, based in the University of Tasmania. Prof Lesley Hughes is an ecologist in the Department of Biological Sciences at Macquarie University and an expert on the impacts of climate change on species and ecosystems. Will Steffen is adjunct professor at the Fenner School of Environment and Society at Australian National University.
Martin Rice is the Research Manager of the Climate Council, an independent non-profit organisation funded by donations from the public. Its mission is to provide authoritative, expert advice to the Australian public on climate change.
John Hunter received funding from the Australian Department of Climate Change and Energy Efficiency.
Lesley Hughes receives funding from the ARC for her work as an ecologist and expert on the impacts of climate change on species and ecosystems. She is the Co-Director of the Climate Futures Research Centre at Macquarie University and the Director of the Biodiversity Node of the NSW Adaptation Research Hub. She is also a member of Climate Scientists Australia and the Wentworth Group of Concerned Scientists.
Will Steffen does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.
This article was originally published on The Conversation. Read the original article here.
