Illustration of a Megalodon shark and great white shark shown for scale
Credit: © Christian Darkin, Science Source

Arriving at the tail end of a long de-bait, scientists have figured out what happened to the megalodons that used to swim in our oceans. Megalodons were the largest sharks that ever lived, reaching an estimated 52 feet (16 meters) long. Megalodon, which means big tooth, lived from about 17 million to 2 million years ago. The fate of the megalodon has stumped scientists and enthusiasts for ages. How did such a powerful and monstrous shark die out?

The megalodon was a powerful predator (hunting animal). Its jaws may have reached about 6 1/2 feet (2 meters) across. Scientists believe it had an exceptionally strong bite. Megalodon’s largest teeth measure about 7 inches (17 centimeters) along their edges. They rank as the largest shark teeth known. A new finding made a splash in the headlines, revealing just how this monster shark became extinct. Extinction occurs when every member of a species (kind) of living thing has died.

The great white shark, shown here, is one of the most dangerous sharks. It has many sharp, triangular teeth. The great white shark can grow to more than 21 feet (6.4 meters) in length.
Credit: © Shutterstock

A new study has shown that maybe those big teeth didn’t help these large predators out much. After studying zinc isotopes in fossils of teeth from great white sharks and megalodons, the scientists reported that great white sharks and megalodons competed for food. Zinc isotopes in teeth reveal where the animal lies on the food chain. When teeth have low levels of zinc, that means the animal is higher on the food chain. The great white shark and megalodon tooth fossils had the same range of zinc isotopes. The two sharks were not chums, they were biting into the same prey! In a feeding frenzy, the great white sharks won, leaving the great big megalodons hungry.

While the great white shark is one of the most dangerous sharks, they can only grow to a little more than 21 feet (6.4 meters) in length. So the megalodon had about 30 feet (9 meters) on them! Unlike most other sharks, great white sharks have warm blood and warm muscles. These characteristics make them faster and stronger than most other sharks. Great white sharks have sharp, triangular teeth with jagged edges. They can rip chunks of flesh from seals and sea lions, two of their favorite prey. It looks like baby shark beat out the bigger shark!

Saltwater crocodile
© Firepac, Shutterstock

October 21 is a special day for our scaly friends. Slithering black mambas, majestic leatherback sea turtles, and itty bitty nano-chameleons (just discovered in 2021) step into the spotlight for National Reptile Awareness Day in the United States.

The saltwater crocodile is the largest living reptile and one of the most fearsome predators (hunting animals) on Earth. Adults can reach lengths of 23 feet (7 meters) and weights of over 1 ton (0.9 metric tons). Saltwater crocodiles live on the coasts of northern Australia and Southeast Asia, and on the islands between. The saltwater crocodile is also called the estuarine crocodile and the Indo-Pacific crocodile. In Australia, it is informally called the “saltie.”

The saltwater crocodile has a long, low, sausage-shaped body; short legs; and a long, powerful tail, which it uses to swim. It also has a tough hide, a long snout, and sharp teeth to grasp its prey.

A saltwater crocodile’s diet depends greatly on its age and size. Young individuals eat crustaceans, insects, rats, and small fish. As saltwater crocodiles grow, they take increasingly larger prey, including sharks and water buffalo. Large adults may attack humans if an opportunity presents itself.

Unlike other crocodiles and alligators, saltwater crocodiles swim in the open ocean. They have occasionally been seen swimming far from shore, apparently moving between islands. Saltwater crocodiles are often found in brackish (salty) pools and estuaries, coastal river valleys flooded by the ocean. They can also live in fresh waters, however, including rivers and swamps.

Saltwater crocodiles reproduce during the rainy season. A female saltwater crocodile lays about 50 eggs in a nest of rotting vegetation. The mother may protect the nest from predators. The eggs hatch in about three months. Hatchlings are about 1 foot (30 centimeters) long at birth. The mother carries the hatchlings from the nest to open water to protect them from land predators.

Male saltwater crocodiles grow larger than females. Males reach an average length of about 16 feet (5 meters). Females typically grow to about 11 1/2 feet (3.5 meters) in length.

Adult saltwater crocodiles have one of the strongest bites in the animal kingdom. They can close their jaws with approximately 3,700 pounds per square inch (16,500 newtons) of force. In contrast, human bite force is only about 200 pounds per square inch (900 newtons).

Because they present a danger to humans, saltwater crocodiles are sometimes feared and hated by people. In northern Australia, they were hunted almost to extinction before a 1970 hunting ban enabled populations to recover. Like most other crocodiles, saltwater crocodiles are threatened by hunting, invasive species, habitat destruction, and pollution. Governments across the saltwater crocodile’s range work to educate people on how to avoid attacks.

June 19, 2014

Evidence of a vast reservoir of water long thought to exist deep within Earth has been revealed in two recent studies. The reservoir, which may contain as much water as all of Earth’s oceans, is more than 300 miles (480 kilometers) below the surface in the mantle, the enormously thick layer of rock between Earth’s crust and inner core. One line of evidence for the reservoir was reported this month by scientists who analyzed seismic waves passing through the mantle beneath the United States. Another line of evidence, reported earlier this year, came from a battered diamond found in Brazil.

Scientists were quick to explain that the reservoir does not look like an underground sea. Instead, the water is locked within tiny grains of a kind of mineral called ringwoodite that forms in the searing temperatures and crushing pressures of the mantle. The water is not even a liquid or a vapor. It consists of hydroxide ions, negatively charged atoms of hydrogen and oxygen bound together. One scientists described the reservoir as a layer of “mushy rock.”

Beneath Earth's solid crust are the mantle, the outer core, and the inner core. Scientists can learn about the inside of Earth by studying how waves from earthquakes travel through the planet. (World Book illustration by Raymond Perlman and Steven Brayfield, Artisan-Chicago)

The seismic evidence was collected by scientists analyzing data collected by the Transportable Array (TA), an ambitious earth science observatory funded by the National Academy of Sciences. The TA consists of hundreds of portable seismic stations that measure waves of energy passing through Earth’s layers during earthquakes or other seismic events. Arranged in a grid pattern, the stations were rolled eastward across North America over a 10-year period. The scientists found that the speed of the waves changed as they passed through a part of the mantle called the transition zone. This suggested that the ringwoodite in this zone was melting. Finding evidence of melting at such an unusual depth, the scientists concluded, indicated that the ringwoodite was releasing water as it was carried deeper into the mantle.

The other study involved an analysis of a diamond shot from the transition zone to the surface through a volcanic eruption called a kimberlite. The diamond, which scientists said, looked like it had been “to hell and back,” contained a sample of water-bearing ringwoodite. It is the only known piece of ringwoodite ever found naturally on Earth’s surface. All other samples of the mineral, which lies too deep to be obtained by drilling, have come from meteorites or have been produced in scientific laboratories.

Scientists said that in addition for providing evidence of Earth’s hidden ocean, the research may shed new light on the movement of the tectonic plates that make up Earth’s outer surface. The findings also bolster the theory that the water in Earth’s oceans and lakes came from rocks that formed early in Earth’s history, not from icy comets that bombarded the surface.

Additional Woirld Book articles:

• Water cycle

Jan. 12, 2012

At least 23 new animal species have been discovered living around hydrothermal vents in the Southern Ocean, near Antarctica. The species include barnacles, sea anemones, starfish, snails, and yeti crabs. The yeti crabs were by far the most abundant species, with heaps of the white creatures jostling for position in the flow of water from the vents. Scientists surveyed the vents using a robotic vehicle tethered to a research ship on the surface. The vents are about 8,000 feet (2,438 meters) beneath the surface.

Hydrothermal vents are areas where heated water flows from the ocean floor. In the Southern Ocean, water exits the vents at temperatures up to up to 720 °F (383 °C), but it quickly cools as it meets the frigid water of the deep Southern Ocean. As the water cools, it releases chemicals that bacteria can use to make their own food. Animals provide the bacteria with a place to live in exchange for food. For example, the yeti crabs are covered in hairlike filaments that house the bacteria.

The deep sea holds some of the most fascinating creatures on Earth. Deep-sea dwellers include the cirrate octopod (an octopus), the tripod fish, and many animals that resemble corals. Other animals live around hydrothermal vents, including tubeworms and mussels. This illustration shows only a few of the creatures from the deep sea. Many of the animals shown in this illustration come from different parts of the deep sea and would not be found living together. World Book illustration by Tony Gibbons, Bernard Thornton Artists

The newly discovered species are unlike those found around other hydrothermal vents, where giant tubeworms, mussels, and shrimp dominate. The scientists believe that harsh conditions in the Southern Ocean probably prevent these animals from colonizing vents there. The researchers expect to identify other new species as they continue to study samples taken from the area.

Scientists have been fascinated by life around hydrothermal vents since the first vent was discovered in 1977. Organisms that live around hydrothermal vents do not depend on the sun for energy, unlike nearly all other life on Earth. Some scientists believe that life first arose around hydrothermal vents. Scientists also speculate that alien planets with harsh environments may support extraterrestrial life similar to the extremophiles found around hydrothermal vents.

Additional articles in World Book:

• Archaea
• Back in Time (Biology 1977)
• Back in Time (Geology 1977)
• Deep sea
• Exploring the Ocean Abyss (A Special Report)