Asked by: Adam King, Huddersfield
The earliest fossils of complex land plants date from around 470 million years ago. They resembled liverworts – a kind of simple moss – and reproduced by releasing spores, which were carried away when it rained.
Spores contain a single cell, whereas a seed contains a multicellular, fertilised embryo that is protected from drying out by a tough coat. These extra features took another 150 million years to evolve, whereupon the first seed-bearing plants emerged. So plants came first, by a long way.