Despite being covered by water, only a tiny fraction — 0.008 percent — of Earth’s freshwater is contained in rivers and lakes. Yet there is astonishing variety among the lakes the of the world. From pink lakes in Australia and Kenya, to lakes filled with harmless jellyfish, lakes provide strange environments for different species of animals and plants. The lakes listed here are some of the most spectacular and unusual that the world has to offer.
Water is the only substance on Earth whose chemical formula has entered the vernacular. We all know H2O, even if we don’t understand precisely what it means. But if it sounds simple, the reality is different. This common, seemingly boring substance baffles and confuses anyone who peers at it for long enough.
Water breaks all the rules. Since the 19th century, chemists have developed a robust framework to describe what liquids are and what they can do. Those ideas are almost useless at explaining the weird behaviour of water. Its strangeness underlies what happens every time you drop an ice cube into a drink. Think about it for a moment: in front of you is a solid, floating on its liquid. Solid wax doesn’t float on melted wax; solid butter doesn’t float on melted butter in a hot saucepan; rocks don’t float on lava when it spews out of a volcano.
Ice floats because water expands when it freezes. If you’ve left a bottle of fizz in the freezer overnight, you’ll know that this expansion is a powerful force: strong enough to shatter glass. This seems like a small and inconsequential curiosity, but this anomaly – one of water’s plethora of strange and unique behaviours – has shaped our planet and the life that exists on it.
Through aeons of cycles of freezing and melting, water has seeped into giant boulders, cracked those rocks apart and broken them up into soil. Ice floats in our drinks, but also across our oceans as sea ice and glittering icebergs. In frozen lakes and rivers, the ice does more than decorate the surface; it insulates the water underneath, keeping it a few degrees above freezing point, even in the harshest of winters.
Water is at its most dense at 4C and, at that temperature, will sink to the bottom of a lake or river. Because bodies of water freeze from the top down, fish, plants and other organisms will almost always have somewhere to survive during seasons of bitter cold, and be able to grow in size and number. Over geological time, this oddity has allowed complex life to survive and evolve despite the Earth’s successive ice ages, periods when fragile life forms would have otherwise been wiped out on the desiccated, frozen ground and – if water behaved like a normal liquid – in solidified seas, too.
This, though, is just the start. Take a glass of water and look at it now. Perhaps the strangest thing about this colourless, odourless liquid is that it is a liquid at all. If water followed the rules, you would see nothing in that glass and our planet would have no oceans at all. All of the water on Earth should exist as only vapour: part of a thick, muggy atmosphere sitting above an inhospitable, bone-dry surface. A water molecule is made from two very light atoms – hydrogen and oxygen – and, at the ambient conditions on the surface of the Earth, it should be a gas. Hydrogen sulphide (H2S), for example, is a gas, even though it is twice the molecular weight of water. Other similar-sized molecules – such as ammonia (NH3) and hydrogen chloride (HCl) – are also gases.