Empiricism is a theory of knowledge that asserts that knowledge comes only or primarily via sensory experience. Empiricism emphasizes evidence, especially as discovered in experiments. It is a fundamental part of the scientific method that all hypotheses and theories must be tested against observations of the natural world rather than resting solely on a priori reasoning, intuition, or revelation.
These dancing celestial hues have been both feared and revered throughout history. Today, although we know their cause – charged particles ejected from the sun reacting with the earth’s atmosphere – they are no less awe-inspiring. Enormous curtains of bright green, red and blue sway among the stars. To see them, you must travel north to the Arctic circle, away from light pollution, on a clear, dark night when the solar winds are blowing. Wait, look up and you might just catch the greatest show on earth.
Nature has been working on these marble caves in Chile for six thousand years by driving the waves to wash the calcium carbonate off of the walls.
A song of ice and fire. These protruding snow pillars are a result of the hot inside fighting the cold outside.
When visitors stumbled upon scores of heavy stones that appeared to have moved across the dried lake bed of Racetrack Playa in California’s Death Valley National Park, leaving a tell-tale trail in their wake, scientists were baffled. How had so many boulders, some weighing 300kg, moved as much as 250m across this remote part of the valley, asks Quora user Farhana Khanum?
Adding to the mystery, some trails were gracefully curved, while others were straight with sudden shifts to the left or right. Who, or what, had moved the stones? A slew of theories emerged, from magnetic fields to alien intervention to dust devils to pranksters.
It took a NASA scientist to crack the case. In 2006, Ralph Lorenz developed a kitchen table model using a small rock frozen in an inch of water in a Tupperware container to demonstrate ice shove, the phenomenon behind the mysterious sailing stones.
In winter, Racetrack Playa fills with water and the lakebed’s stones become encased in ice. Thanks to ice’s buoyancy, even a light breeze can send those frozen boulders sailing across the muddy bottom of the lakebed. Stones with rough bottoms leave straight tracks, while those with smooth bottoms drift and digress. Warmer months melt the ice and evaporate the water, leaving only the stones and their mysterious trails.
People can see these sailing stones in a few locations, including Little Bonne Claire Playa in Nevada and most famously, Death Valley’s Racetrack Playa.
Blood Falls, in East Antarctica’s McMurdo Dry Valleys, looks like slowly pouring scarlet-red blood, staining snowy white Taylor Glacier and Lake Bonney below.
The trickling crimson liquid isn’t blood, however. Nor is it water dyed by red algae, as early Antarctica pioneers first speculated. In fact, the brilliant ochre tint comes from an extremely salty sub-glacial lake, explains Quora user Aditya Bhardwaj.
About two million years ago, a hyper-saline body of water became trapped beneath Taylor Glacier, isolated from light, oxygen and heat. As the saltwater trickles through a fissure in the glacier, it reacts with the oxygen in the air to create this spectacular, rust-hued cascade.