Giant Steps Are What We Take

It's forty-three years after Neil Armstrong and Buzz Aldrin walked on the Moon, but their footprints are still preserved in the lunar dust.  In High-resolution images taken by the Lunar Reconnaissance Orbiter their tracks around the Lunar Module and the science packages they deployed show up as dark trails in the Lunar soil.  With no wind or water to erode them, they'll last a long time, but not forever.  Bombardment by micrometeorites will erode them at a rate of about a millimetre per million years; eventually, after ten to a hundred million years, they'll be ground down into the surrounding soil.  Space archaeologists are already making plans to preserve them.

In his terrific new book, The Old Ways: A Journey on Foot, Robert MacFarlane describes walking alongside 5000 year old human footprints preserved in silt in Morecombe Bay.  Volcanic ash in Laetoli, Tanzania, preserved the footprints of Australopithecus afarensis individuals some 3.6 million years ago (there's a nice diorama of this in the New York Museum of Natural History).  There are many trackways of dinosaurs much older, including 250 million year old prints left by a cat-sized dinosauromorph, an early ancestor of dinosaurs, preserved in what was once the mud of the floodplain of a large meandering river.  And the oldest known animal tracks are around 585 million years old, created by a tiny, unknown, soft-bodied creature that's left no other trace.  We humans have some way to go to match that record.