In the end, this is a story about what very small things can contain.

A milk tooth is a tiny object.

It fits easily in a child’s palm.

It weighs almost nothing.

It is the most ephemeral kind of human biological material — shed in childhood, replaced by permanent teeth, typically not preserved in any special way.

Parents sometimes keep them as sentimental objects.

Biology disposes of them as part of the ordinary process of development.

In the permafrost of Siberia, two of these ordinary objects were preserved for 31,000 years.