Might life be simpler than you thought? The work of Richard Long makes you wonder. It sets out to clarify, not to complicate: and how often we need that as we struggle amid our mindjumbling modern world.

Altermodern was the last show that Tate Britain put on. A sprawling hotch-potch of a survey of the contemporary scene, it overloaded the senses and cluttered the head. Long’s Heaven and Earth will feel like a detox programme in comparison. Here, in a slow meditative wander through a career that has spanned more than four decades, visitors can discover a vision to cleanse the confusion. It’s like swapping a sticky cocktail (complete with cherry and parasol) for a glass of sparkling, cold water on a hot summer’s day.

Long’s work has a lovely elemental lucidity. It has been there right from the beginning. He was an 18-year-old West Country art student in 1966 when, one snowy day, he walked on to the Downs above Bristol and started rolling a snowball. When it had grown so big that he couldn’t push it any farther, he took a photograph of it and the meandering track that its making had left and went home.

That ephemeral mark in the melting snow became the starting line of a fresh way of thinking. Until then sculpture had been concerned with the making of objects. But, with the Sixties, a progressive new era was dawning. And Long, going on to study at St Martin’s alongside such fellow radicals as Gilbert & George, wanted to release art from the cage of tradition, to let it run free in a far wider world.

He set out on walks and cycle rides and hitch-hiking expeditions that he labelled “sculptures” and, in doing so, laid the ground for a language that he has been developing ever since. Sculpture, he suggested, could be about place and time as well as material and form. Brought out of the gallery into the rural landscape, using natural materials such as grass, stones and water, it could move into a far wider imaginative dimension.

This new Tate survey of Long’s career has a wonderfully spacious, relaxed, light-flooded feel. Following a vague chronological flow, it invites the visitor to contemplate the artist’s journey from the shaggy pelts of Dartmoor, which as a boy he would tramp with his father, to the Anywhere of an 11-day winter walk that he made last year.

In between, he wanders about all over the place, from the mud of the River Avon through the canyons of Mexico to the paddy fields of India; from the Australian Outback through Bolivian lakesides to misty Japanese peaks. On the way, he goes kayaking down the Columbia River, crosses beaver dams in the Adirondacks, claps together two flat stones 1,000 times in the Sahara and throws rocks around in McGillicuddy’s Reeks.

Sometimes one feels the strong pull of ideas. In 1979, for instance, Long walks from Windmill Hill in Shropshire, the home of the first inhabitants of England to make permanent changes to the landscape, to Coalbrookdale on the River Severn, the birthplace of the Industrial Revolution and the site of the famous Iron Bridge. But this sense of progression soon drifts and dissolves in a realm in which ideas move outwards and not simply onwards: a bit like ripples on the water, repeating and expanding and broadening before merging back into the whole. In 2008 he echoes this early journey in his 603-mile “megalithic to subatomic” tramp from the menhirs of Carnac in France to the CERN particle physics laboratory in Switzerland. At the heart of all his experiences is a fundamental continuity.

The souvenirs that Long brings back to the gallery are wilfully understated. Here, for instance, are photographic records of the ephemeral adjustments he has made as he has wandered along: images of assorted straight lines and circles and henges and cairns that he has trampled across meadows, scuffed into sand, cut out of turf, stacked up with stones, assembled with sticks or formed out of fire ash. But don’t expect lush productions or picturesque dramas. Long is not interested in film’s technological possibilities. For all that he was among the first to explore a new role for the camera in art, he does not reduce the work to a mere image.

There are elements of the natural world transported directly into the gallery: the trademark mud pieces that he slip-slaps across entire walls, plaited and undulating, smeared and dripping or, in the case of the mesmerising White Water Line, pouring like rain in the blackness of the night. Here are heaps of stones heaved indoors and arranged so that one expansive gallery is occupied by a series of geometrical patterns on the floor: a circle of lumpy Norfolk flints that seem almost to be milling about like flocked sheep; an ellipse of basalt that gleams and heaves like some still unsettled primeval volcanic surface.

There are also textual records of Long’s journeys — sparse lists of facts and fragments of thoughts printed, in the case of this show, directly on to the walls to highlight their ephemeral nature (though they do also exist as framed posters). These text works are the most conceptual, and yet at the same time the most viscerally evocative of his pieces. They work like the words that drop into your mind as you walk, churning and rolling in the imagination as you let it wander farther and farther into the world that they conjure: an elemental realm of thunderstorms and roaring rivers, of white butterflies and slippery boulders, of rainbows and circling buzzards.

Long’s art could hardly be farther from artifice. Austere, stringent, pragmatic, it has an almost monastic rigour. The less that he does, the slighter his interventions, the lighter his touch, the more successful his pieces can become. A few upturned stones can articulate an awareness of eternity. Simple words become mantras that evoke cosmic moods.

Following the time-honoured tradition of the ancient peripatetic philosophers, the medieval troubadours, the Lakeland Romantics, Long leads us on a voyage in which it is the movement itself that makes sense. His solitary human figure is like a calibrating mark on a vast natural canvas. A mote caught up in that fundamental flux between the formal and the free, it helps to articulate relationships between ourselves and wider universal forces. It heightens our sense of attunement, speaking of harmonies and rhythms.

Music certainly means a lot to Long. There are references to the lyrics of Bob Dylan and Johnny Cash in his pieces. His body of work builds up like a musical melody. It may be made up of individual notes, but as a whole it amounts to far more than the sum of its parts. And, like a traveller screwing up his eyes to see farther, the longer you look the more you find yourself scrying into ever more distant horizons that a contemplative appreciation of his work can open up.

But it takes time. And for those brought up in a fast-paced world obsessed with innovation and the latest new face, a journey through his oeuvre could soon start to feel like a repetitive plod. Perhaps it’s hardly surprising that Long, for all that he has been lauded (he represented Britain at the Venice Biennale in 1976 and won the Turner Prize in 1989), has fallen out of fashion. It is 18 years, apparently, since a London gallery showed a survey on this scale.

Long is unperturbed. He is a man with a quest. Perhaps no other contemporary has followed his slow-burning faith with such unswerving sincerity, stood so chastely aloof from the temptations of the modern, or pursued his visions with such puritanical rigour. In the flash, brash world of Brit Art, Long has stood for decades like a man apart.

Now, his time comes round again. As global economic collapse brings fantasies tumbling, Long shows us a world with which we can keep faith. This is a show to uncloud your head. It feels as sharp and clear as a gulp of pure mountain air.

Richard Long: Heaven and Earth is at Tate Britain, London SW1 (020-7887 8888; www.tate.org.uk), from tomorrow to Sept 6

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