Every year, millions of tourists flock to Northern Ireland to visit Giant's Causeway - an unusual formation of around 40,000 hexagonal stone columns descending gently into the sea. Theories on the stones' formation range from them being built by a mythical giant Finn McCool to more scientific explanations. Now, Dr Mike Simms, curator of natural sciences at National Museums NI, has put forward the first new theory since 1940. Dr Simms considered why the extraordinary geological features are found at sea level only. To mark Unesco's International Geodiversity Day today, he has explained why he believes they were caused by an event which took just days - and not thousands of years as previously thought.

A newly discovered network of'lost' ancient cities has been discovered in the Amazon, using lidar technology – dubbed'lasers in the sky' – to peer through the tropical forest canopy. The cities, built by the Casarabe communities between 500-1400 AD, are located in the Llanos de Mojos savannah-forest, Bolivia, and have been hidden under the thick tree canopies for centuries. They feature an array of elaborate and intricate structures unlike any previously discovered in the region, including 16ft-high terraces covering 54 acres – the equivalent of 30 football pitches – and 69ft-tall conical pyramids. The international team of researchers from the UK and Germany also found a vast network of reservoirs, causeways and checkpoints, spanning several miles. The discovery challenges the view of Amazonia as a historically'pristine' landscape, the researchers say, showing it was instead home to an early'urbanism' created and managed by indigenous populations for thousands of years.

Causeway is a system for detecting explicit causal relations in text. It tags text using the BECAUSE 1.0 annotation scheme, described in Dunietz et al., 2015. The system itself is described in Dunietz et al., 2017. Note that the repository includes some code for reading in data in an updated version of the annotation scheme (BECAUSE 2.x). This newer scheme is backwards-compatible with the original.

Stunning new maps covering over 2,000 square kilometers of northern Guatemala have revealed the site of an ancient Maya mega-city hidden in the dense tropical forest. Researchers uncovered more than 61,000 ancient structures at the site using LiDAR technology, which relies on laser pulses to map out the topography. Evidence from the exhaustive survey supports earlier suspicions that upwards of 11 million people lived in the Maya Lowlands from the year 650 to 800 CE. Stunning new maps covering over 2,000 square kilometers of northern Guatemala have revealed the site of an ancient Maya megacity hidden in the dense tropical forest. The researchers have now published the results of what they say is the largest LiDAR survey to date, months after first revealing their remarkable discovery.