The only place that life could exist on this planet 540 million years ago was underthe sea. But as oxygen levels rose on the surface, a few brave pioneers took their first steps on to dry land. As Peter Evans discovers, scientists in Canada have recently unearthed remarkable evidence of one of these early landing parties. What were these creatures and why did they decide to leave the sea for life on terra firma? EMAIL: radioscience@bbc.co.uk Producer Rami Tzabar