The first whales originated roughly 50 million years ago from land animals that crawled into the sea, gradually trading in their legs for flippers.
“There are so many changes from their terrestrial ancestors,” says Olivier Lambert, a palaeontologist at the Museum of Natural Sciences in Brussels, and lead study author.
Life changed completely on the island on August 12, 1953 when an earthquake of great magnitude (7.2 on the Richter scale) hit Greece.
“This is the fossil that we’ve been waiting for,” says Nick Pyenson, a palaeontologist at the Smithsonian National Museum of Natural History in Washington DC.
Relative age dating also means paying attention to crosscutting relationships.
Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.
The Law of Superposition, which states that older layers will be deeper in a site than more recent layers, was the summary outcome of 'relative dating' as observed in geology from the 17th century to the early 20th century.
The regular order of occurrence of fossils in rock layers was discovered around 1800 by William Smith.