The oldest microfossils ever found were discovered in a 3.4 billion-year-old sandstone at the base of Strelley Pool in the remote Pilbara region of Western Australia.
Aug. 30, 2011 --
Evolution and natural selection have played a role in the ever-changing landscape of plants, animals, bacteria and fungi. Although species evolve as they find their niche and adapt to new opportunities, some animals have remained relatively unchanged over the course of history. These animals are known as living fossils. Compared to the animals on this list, humans are relative newcomers to this planet. Homo sapiens emerged out of Africa a mere 200,000 years ago. Many living fossils are considerably older than humans and other mammals; some have even outlasted the dinosaurs. In this slideshow, take an up-close look at animals that have persevered virtually unchanged through the ages and continue to thrive today. We begin with the platypus, an unusual egg-laying animal with fur, a bill and a venomous bite. Charles Darwin himself coined the term "living fossil" while observing the platypus. Native to eastern Australia, the animal is the only surviving example of its family, Ornithorhynchidae. This group of animals is believed to have split from mammals some 166 million years ago.
The horseshoe crab could hold the distinction of being the oldest animal species still in existence. Dating back to the Paleozoic era, the horseshoe crab existed on Earth before the dinosaurs and soldiered on through several mass extinction events. In 2008, a horseshoe crab fossil, the oldest in existence found so far, dated back to around 445 million years ago, according to a report by LiveScience.
The tadpole shrimp, Triops cancriformis, is another contender for the title of oldest living animal species. This shrimp is related to the horseshoe crab so its longevity should come as no surprise. According to a report by The Telegraph, the tadpole shrimp as it appears today is virtually identical to a fossil of a specimen that lived some 200 million years ago just as dinosaurs rose to prominence. Despite the animal's remarkable endurance, the tadpole shrimp is currently listed as an endangered species.
Once thought to be extinct in the same event that killed off the dinosaurs some 65 million years ago, the coelacanth is a lobe-finned fish that sparked a debate over whether this species represented a missing link between aquatic animals and four-legged terrestrial creatures, according to National Geographic. The animal was rediscovered in 1938 and only two species of coelacanth still exist today. In 2007, a fossilized coelacanth fin was found dating back roughly 400 million years.
Snapping turtles as we know them first walked the earth some 40 million years ago, but they have been virtually unchanged over the past 215 million years of their evolution, according to Tortoise Trust. Although not among the most endangered tortoises and turtles according to the Turtle Conservation Coalition, the snapping turtle is listed as threatened.
The more than 20 species of alligators and crocodiles living today have evolved beyond their more primitive ancestors. But the basic physical design of these reptiles has remained essentially the same for the past 320 million years or so. Alligators and crocodiles share a common ancestry, though the two groups separated from each other some 60 million years ago.
The nautilus is the most primitive cephalopod in existence, a group that includes the most complex squid and octopus. Dating back to more than half a billion years ago, the nautilus reached the high point in its evolution during the Paleozoic era about 505 million to 408 million years ago. Several species of nautilus still survive today -- relatively unchanged from their ancestral counterparts.
Goblin sharks are rare, deep-sea dwellers with a unique elongated nose that distinguishes them from other sharks. They're also ancient, and are between 112 million to 124 million years old as a species. Around 2,000 different species of fossil sharks have been discovered, according to the ReefQuest Centre for Shark Research. The earliest sharks predate the dinosaurs by more than 200 million years.
The cockroach is famous for being a survivor. These insects can survive for weeks without their heads and even withstand the fallout following a nuclear blast. Cockroaches are also an especially long-surviving animal. Roaches have thrived on Earth for some 320 million years, with an estimated 5 million to 10 million individual species ranging in shape, size and habitat. This photo shows Blaberus giganteus, one of the largest species of cockroach on Earth.
Hagfish may have had to endure a less-than-flattering name since scientists first described them in the 18th century. However, these famously ugly marine animals have existed for about half a billion years. The hagfish also represents an important evolutionary step in the development of vision. These ancient fish may have been among the earliest animals to evolve more complex, camera-like eyes as opposed to the strictly photosensitive vision possessed by more primitive species. As such, the hagfish represents a kind of missing link in the evolution of the eye.
— Microfossils of bacteria living 3.4 billion years ago were found in Australia.
— Earth had no oxygen at the time the bacteria existed.
— The finding from a remote region of Western Australia lends hope that life has existed on Mars.
Microfossils found in Australia show that more than 3.4 billion years ago, bacteria thrived on an Earth that had no oxygen, a finding that boosts hopes life has existed on Mars, a study published Sunday says.
Researchers from the University of Western Australia and Oxford University say the remains of microbes, located in ancient sedimentary rocks that have triggered debate for nearly a decade, have been confirmed as the earliest fossils ever recorded.
The sample came from the remote Pilbara region of Western Australia, a site called Strelley Pool, where the microbes, after dying, had been finely preserved between quartz sand grains.
Pilbara has some of the planet's oldest rock formations, set down in the so-called Archean Eon when the infant Earth was a primeval water world, with seas that were the temperature of a hot bath.
In 2002, another team of scientists, working in the same region just 35 kilometers (20 miles) away, said they had found bacteria fossils in the same formation.
But the claim was disputed, with some experts saying that the tiny pockmarks were not the signatures of once-living organisms but the result of mineralization of the rocks.
Drawing on the latest electron microscopy and spectroscopy techniques, the authors of the new study say they have triple proof that their sample is biological in origin.
The microbes fed on sulphur compounds to survive, they believe.
The marks measure only about 10 millionths of a meter (0.0004 inches) long.
Their shape and clustering are not only consistent with bacterial cells, say the scientists.
They also have minute crystals of pyrite, an iron-and-sulphur compound also known as fool's gold, which are a clear by-product of metabolising sulphur and sulphates, according to their argument.
The team, led by David Wacey of the University of Western Australia, report the finding in the journal Nature Geoscience.
"At last we have good solid evidence for life over 3.4 billion years ago. It confirms there were bacteria at this time, living without oxygen," Martin Brasier, a professor at Oxford University, said in a press release.
Sulphur-loving bacteria "are still common today," said Brasier.
The bugs are found in smelly ditches and soil but also as "extremophiles" in hot springs and thermal vents in the deep ocean.
"Could these sorts of things exist on Mars? It's just about conceivable,' said Brasier.
Robots or astronauts sent to the Red Planet could look at Pilbara-like sites to find out. However, their samples would have to undergo similar scrutiny to support beliefs that life has existed on Earth's enigmatic neighbor.