Clay may have been the birthplace of life on Earth despite being a seemingly infertile and inhospitable blend of minerals, some U.S. scientists say.

Life, or at least the complex biochemicals that make life possible, could have formed within a kind of clay known as a hydrogel, containing a mass of microscopic spaces capable of soaking up liquids like a sponge, Cornell University biological engineers report in the journal Scientific Reports.

"We propose that in early geological history clay hydrogel provided a confinement function for biomolecules and biochemical reactions," biological and environmental engineering Professor Dan Luo said.

In seawater, clay forms a hydrogel, and over billions of years chemicals confined in those spaces could have carried out the complex reactions that formed proteins, DNA and eventually all the machinery that make a living cell work, the Cornell researchers suggest.

The noted that geological history shows clay first appeared on Earth -- as silicates leached from rocks -- just at the time biomolecules began to form into protocells and eventually membrane-enclosed cells.

The geological events matched nicely with biological events, they said.