Enlarge (credit: Hal Beral)

For many creatures, having a limb caught in a predator’s mouth is usually a death sentence. Not starfish, though—they can detach the limb and leave the predator something to chew on while they crawl away. But how can they pull this off?

Starfish and some other animals (including lizards and salamanders) are capable of autonomy (shedding a limb when attacked). The biology behind this phenomenon in starfish was largely unknown until now. An international team of researchers led by Maurice Elphick, professor of Animal Physiology and Neuroscience at Queen Mary University of London, have found that a neurohormone released by starfish is largely responsible for detaching limbs that end up in a predator’s jaws.

So how does this neurohormone (specifically a neuropeptide) let the starfish get away? When a starfish is under stress from a predatory attack, this hormone is secreted, stimulating a muscle at the base of the animal’s arm that allows the arm to break off.

Enlarge / Artist's conception of the state of the Earth during its global glaciations. (credit: NASA)

Earth has gone through many geologic phases, but it did have one striking period of stasis: Our planet experienced a tropical environment where algae and single-celled organisms flourished for almost 2 billion years. Then things changed drastically as the planet was plunged into a deep freeze.

It was previously unclear when Earth became a gargantuan freezer. Now, University College London researchers have found evidence in an outcrop of rocks in Scotland, known as the Port Askaig Formation, that show evidence of the transition from a tropical Earth to a frozen one 717 million years ago. This marks the onset of the Sturtian glaciation and would be the first of two "snowball Earth" events during which much of the planet’s surface was covered in ice. It is thought that multicellular life began to emerge after Earth thawed.

Found in the Scottish islands known as the Garvellachs, this outcrop within the Port Askaig Formation is unique because it offers the first conclusive evidence of when a tropical Earth froze over—underlying layers that are a timeline from a warmer era to a frigid one. Other rocks that formed during the same time period in other parts of the world lack this transitional evidence because ancient glaciers most likely scraped it off.