It's a typical November Tuesday for Mary, who lives in the northeast of the United States.

She's 44, has a degree and her family is prosperous.

So how has she been spending her day? Is she a lawyer pleading a case, a teacher in front

of a class of kids, a management consultant surfing a spreadsheet?

Well known. Mary spent an hour knitting and sewing, two hours setting the table and doing

the dishes and well over two hours preparing and cooking food and in this she isn't unusual.

This is because it's 1965 and in 1965 many married American women, even those with an excellent

education, spent large chunks of their day catering for their families. For these women,

putting food on the table wasn't a metaphor. It was something that they did quite literally

and it took many hours each week. We know about Mary's day and the days of many other people

because of time use surveys conducted around the world. These are diaries of exactly how different

sorts of people use their time. And for educated women, the way time is spent in the United States

and other rich countries has changed radically over the past half a century. Women in the US now

spend around 45 minutes per day on cooking and cleaning up. That's still much more than men

who spend just 15 minutes a day, but it's a vast shift from Mary's four hours a day.

The reason for this shift is because of a radical change in the way the food we eat is prepared.

If you want a symbol of this change, it's the introduction in 1954 of the TV dinner.

Presented in a space-age aluminium tray and prepared so that the meat and the vegetables would

all require the same cooking time. The frozen turkey tray TV dinner was developed by a bacteriologist

called Betty Cronin. She worked for the Swanson Food Processing Company, which was looking for ways

to keep busy after the business of supplying rations to US troops had dried up. But of course,

the TV dinner was just part of a panoply of changes, wrought by the availability of freezers,

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