The First Law of Technology says we invariably overestimate the short-term impact of new technologies while underestimating their longer-term effects. The invention of printing in the 15th century had an extraordinary short-term impact: though scholars argue about the precise number, within 40 years of the first Gutenberg bible between eight and 24 million books, representing 30,000 titles, had been printed and published. To those around at the time, it seemed like a pretty big deal.

'In our time', wrote German humanist Sebastian Brandt in 1500, '...books have emerged in lavish numbers. A book that once would've belonged only to the rich - nay, to a king - can now be seen under a modest roof... There is nothing nowadays that our children... fail to know.' They didn't know the half of it.

They didn't know, for example, that Gutenberg's technology, which enabled lay people to read and interpret the bible for themselves, would undermine the authority of the Catholic church and fuel the Reformation. Or that it would enable the rise of modern science by facilitating the rapid and accurate dissemination of ideas. Or create new social classes of clerks, teachers and intellectuals. Or alter our conception of 'childhood' as a protected early stage in the lives of young people. In an oral culture, childhood effectively ended at the age when an individual could be regarded as a competent communicator, ie, about seven - which is why the Vatican defined that as 'the age of reason' after which individuals could be held accountable for their sins.

In a print-based culture, communicative competence took longer to achieve and required schooling, so 'childhood' was extended to 12 or 14. All these long-term impacts were not - indeed, could not have been - foreseen. Yet they represent the profound ways in which Gutenberg's technology transformed society.

Today's Gutenberg is Sir Tim Berners-Lee, inventor of the web. In the 17 years since he launched his technology on an unsuspecting world, he has transformed it. Nobody knows how big the web is now, but estimates of the indexed part hover at around 40 billion pages, and the 'deep web' hidden from search engines is between 400 and 750 times bigger than that. These numbers seem as remarkable to us as the avalanche of printed books seemed to Brandt. But the First Law holds we don't know the half of it, and it will be decades before we have any real understanding of what Berners-Lee hath wrought.

Occasionally, we get a fleeting glimpse of what's happening. One was provided last week by the report of a study by the British Library and researchers at University College London. The study (available from tinyurl.com/2eslnr) combined a review of published literature on the information-seeking behaviour of young people more than 30 years with a five-year analysis of the logs of a British Library website and another popular research site that documents people's behaviour in finding and reading information online.

The findings describe 'a new form of information-seeking behaviour' characterised as being 'horizontal, bouncing, checking and viewing in nature. Users are promiscuous, diverse and volatile.' 'Horizontal' information-seeking means 'a form of skimming activity, where people view just one or two pages from an academic site then "bounce" out, perhaps never to return.' The average times users spend on e-book and e-journal sites are very short: typically four and eight minutes respectively.

'It is clear', says the study, 'that users are not reading online in the traditional sense, indeed there are signs that new forms of "reading" are emerging as users "power browse" horizontally through titles, contents pages and abstracts, going for quick wins. It almost seems that they go online to avoid reading in the traditional sense.' These findings apply to online information seekers of all ages.

The study confirms what many are beginning to suspect: that the web is having a profound impact on how we conceptualise, seek, evaluate and use information. What Marshall McLuhan called 'the Gutenberg galaxy' - that universe of linear exposition, quiet contemplation, disciplined reading and study - is imploding, and we don't know if what will replace it will be better or worse. But at least you can find the Wikipedia entry for 'Gutenberg galaxy' in 0.34 seconds.

john.naughton@observer.co.uk