Scientists have many theories about how Earth's raw materials turned into living cells, but a new proposal is particularly slimy. In a recent paper, an international team argues that life may have first emerged within a blob of sticky goo clinging to a rock, long before true cells existed. Similar to the bacterial biofilms we see today on rocks , pond surfaces , and even your unbrushed teeth , a semi-solid gel matrix would provide the perfect place for life to set up shop, the authors propose ,