Sharks Are Older Than Trees (And 7 Other Facts That Will Blow Your Mind)

Sharks were swimming through Earth's oceans before trees existed. Shark-like fish go back roughly 450 million years, and the first trees appeared about 385 million years ago. Here are eight facts about them, starting with that one.

1. Sharks Are Older Than Trees

The earliest shark-like creatures appear in the fossil record around 450 million years ago, during the Ordovician period, as scattered scales from Colorado, Mongolia and elsewhere. Whether those scales belong to true sharks or to close relatives in the cartilaginous fish lineage is still debated, which is worth knowing before anyone builds too much on the number. Trees, by comparison, didn't evolve until the Devonian, roughly 385 million years ago, when Archaeopteris began forming the first forests. Even on the cautious reading, sharks got there first by tens of millions of years, and the lineage has come through the mass extinctions since, including the one that finished the dinosaurs.

Most of that record is teeth and scales, for a reason built into the animal: a shark's skeleton is cartilage, not bone. Cartilage is lighter and more flexible, which helps with agility and buoyancy, but it rarely fossilizes. Teeth preserve extremely well, so much of what is known about ancient sharks comes from them.

2. Some Sharks Glow Under Blue Light

Deep beneath the ocean's surface, where sunlight can't reach, certain sharks have evolved a remarkable trick: biofluorescence. Species like the chain catshark (Scyliorhinus retifer) and the swell shark absorb blue light from the water and re-emit it as a vivid green glow, invisible to most predators but clearly visible to other sharks of the same species.

Biofluorescence requires ambient blue light to work, so these sharks do not produce visible glow in true darkness. In the blue-lit depths where they live, however, their re-emitted green glow is vivid and clearly visible to other members of their species.

3. Shark Skin Is Made of Tiny Teeth, and Swimsuit Makers Took Notes

Run your hand along a shark from head to tail and it feels smooth. Run it the other way and it feels like sandpaper. That's because shark skin is covered in thousands of microscopic tooth-like scales called dermal denticles, which are structurally almost identical to teeth.

Speedo marketed the Fastskin swimsuit as shark-skin-inspired, but a 2012 study by Oeffner and Lauder in the Journal of Experimental Biology found no consistent improvement in swimming performance from the Fastskin fabric itself. Engineered riblet surfaces that more closely replicate denticle geometry have shown genuine drag reduction in controlled tests.

4. Some Sharks Sleep While Swimming

Many sharks need to keep moving to breathe (a process called ram ventilation) where water flows over the gills as the shark swims forward. Whether sharks that must keep swimming to breathe can rest in any comparable way remains an open question.

A 2022 study in Biology Letters by Kelly et al. confirmed sleep-like states in benthic draughtsboard sharks, marked by reduced metabolism and postural relaxation. How or whether ram-ventilating sharks that cannot stop swimming achieve rest has not been tested. The spinal cord may handle swimming mechanics independently of higher brain activity in some species, but this remains a hypothesis rather than an established fact.

5. Sharks Can Detect Your Heartbeat

Sharks possess one of the most extraordinary sensory systems in the animal kingdom: electroreception. Tiny, gel-filled pores on their snouts called the ampullae of Lorenzini can detect the faint electrical fields generated by the muscle contractions of living creatures, including a beating heart.

This means a shark can find prey hiding under sand, in murky water, or in complete darkness, detecting the electrical signature of a living body. It is not working alone. The lateral line running along each side of the body picks up pressure changes and vibrations from nearby animals, and together with electroreception and smell it gives a shark several ways to find prey it cannot see.

6. The Greenland Shark Can Live for Centuries

If you thought sharks were impressive already, meet the Greenland shark (Somniosus microcephalus), the longest-lived vertebrate on Earth. A 2016 study published in Science used radiocarbon dating of eye lens proteins to estimate that one female Greenland shark was approximately 392 years old, with a possible range of 272 to 512 years. That means she may have been alive in the early 17th century. Only sharks near the top of the estimated range, around 512 years old, would have been alive during the reign of Queen Elizabeth I, who died in 1603.

Greenland sharks grow at a glacial pace (about one centimeter per year) and don't reach sexual maturity until they're around 150 years old. They cruise through the frigid Arctic and North Atlantic waters at a leisurely pace, seemingly in no hurry whatsoever. When you've got centuries to spare, why rush? They share that frigid range with the narwhal, the Arctic's real unicorn, another long-lived neighbor whose age scientists also read from the chemistry of its eye lens.

Sharks have more surprises still. Here are two more.

7. Whale Sharks Are the Largest Fish on Earth

The whale shark is the largest fish on Earth, and the largest specimen reliably measured reached 18.8 meters (about 62 feet). Despite their enormous size, whale sharks feed almost exclusively on tiny plankton, fish eggs, and small crustaceans, filtering vast quantities of water through their gills. They are entirely harmless to humans.

8. Some Sharks Are Warm-Blooded

Most fish are cold-blooded, but species such as the great white shark and the shortfin mako can regulate parts of their body temperature above the surrounding water, a trait called regional endothermy. Warmer muscles and eyes give these sharks a speed and sensory advantage over prey in cold water. It is one of several traits that distinguish the most active shark species from their more sedentary relatives.

The Ocean's Most Extraordinary Survivors

Sharks aren't just ancient; they're masterpieces of natural engineering. From biofluorescing under blue light to sensing heartbeats with extraordinary precision, from surviving five mass extinctions to reaching nearly 20 meters in length, these animals have earned every bit of awe and respect we can give them. And yet, despite their incredible resilience, many shark species are now threatened by overfishing, habitat loss, and the shark fin trade.

The more we learn about sharks, the harder it is not to be completely captivated by them. They're not the mindless killing machines of Hollywood legend; they're sophisticated, ancient, and utterly irreplaceable parts of our ocean ecosystems. Eight facts barely scratch a lineage that has been evolving for 450 million years.

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A shark replaces its teeth continuously for its whole life, one of the things the shark Beastfile collects.

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