How long ago was the earliest life on earth

Others had a bush, or cabbage-like appearance. Many looked like shapeless sacs, or thin, quilted pillows, while others bore a resemblance to enormous sea pens. Namibia is one of the only places that records the transition between the Ediacaran and Cambrian periods Credit: Simon Darroch.

The bizarre forms and body plans have long baffled scientists, who have struggled to place the creatures in the tree of life. Most of the ancestors of modern animals can be traced to this point. However the biggest mystery surrounding the Ediacarans is what happened to them. At one point they must have been thriving: fossils of rangeomorphs and others have been discovered in locations all over the world; from Russia to Australia, and Namibia to China.

However, they suddenly disappeared from the fossil record approximately 30 million years after they first arrived. Some million years ago, the Earth was thawing its way out of an ice age, and this area was flooded with glacial water, forming a shallow sea. You can walk for hundreds of miles in any direction and see records of the animals that lived there, displayed on the surface of rocks.

Life became more widespread and complicated during the 'Cambrian Explosion' some million years ago Credit: Getty Images. In , Darroch found vast fields of what looked remarkably like burrows made in the Nama sediment — signs that these younger animals were foraging, and churning up the seafloor. Some scientists doubt that they are the remains of microbes at all. Others note that the age of the crystals cradling the potential microfossils is controversial, and the structures may be more than a billion years younger than reported.

Rather than looking for tiny fossils, the team was searching for something more subtle: The organic fingerprints of early organisms. The team sliced their rocky clutch into thin sections. Taking a close look with a microscope, scientists noticed the fossils, which are tucked into crystals embedded in the rocks. Though minuscule, the structures were remarkably intricate and complex, and that made the team suspect they were seeing something more important than organic fingerprints.

In , scientists peering at a Martian meteorite recovered from Antarctica also spotted what looked like the tube-shaped remnants of organisms. The discovery ignited arguments that continue to this day , although the general scientific consensus is that the Martian structures are not of biological origin.

Perhaps with that in mind, Dodd and his colleagues set out to carefully prove that their structures were created by something with a metabolism and not simply by rocks and seawater. They studied the materials around the fossils for signs of biological processes, and they found carbon-containing compounds arranged in rosettes, which seemed to carry an imprint revealing biological processing.

The fossils were also surrounded by minerals containing phosphorus, an element incorporated into the building blocks of life and released by decaying organisms. The team also compared the microfossils with million-year-old microbial structures formed around an ancient vent in present-day Norway, million-year-old structures from vents in the U.

The similarities were striking. Altogether, the evidence suggests life made the ancient sheaths, the team concludes in their study, published today in the journal Nature. But not everyone is convinced. Based on two different isotopic clocks used to date the rocks, Dodd and his colleagues suggest the microfossils could be as young as 3.

But scientists such as Kelly maintain that in such complex rocks, determining the relative ages of features is difficult, and assigning such an ancient age to the fossils is not accurate. At this time, the entire Nuvvuagittuq formation was substantially altered by tectonically driven cycles of high pressure and temperature, which could have stretched, bent, and distorted the rocks, destroying any existing fossils. Dodd counters with previous evidence that fossils can survive such punishing environments, pointing to the Greenland microbes and fossilized plants and spores in New Zealand.

In particular, icy ocean worlds orbiting Jupiter and Saturn are thought be among the best places to search for life beyond Earth. For Enceladus, there are quite direct indications of hydrothermal vents. From what is known of this period, there would have been liquid water on the planet, Bell told Live Science in an interview. There might have been granite, continental-like crust, though that's controversial, she said. Any life that could have existed would have been a prokaryote a single-celled organism without membrane-bound nuclei or cell organelles , Bell added.

If there was continental crust on Earth at the time, she said, prokaryotes might have had mineral sources of nutrients like phosphorus. A different approach to the hunt for Earth's early life suggests that oceanic hydrothermal vents may have hosted the first living things.

In a paper published in July in the journal Nature Microbiology , researchers analyzed prokaryotes to find the proteins and genes common to all of these organisms, presumably the final remnants of the Last Universal Common Ancestor LUCA — the first shared relative from which all life today descends. The research team found proteins shared by all archaeal and bacterial lineages.

Based on those proteins, the researchers reconstructed a view of LUCA's genome, hinting that it lived in an anaerobic oxygen-free , hydrothermal environment. If that's the case, Earth's first life or at least the first life that left descendants would have resembled the microbes that cluster around deep-sea vents today, the researchers said.

Original article on Live Science. Stephanie Pappas is a contributing writer for Live Science covering topics from geoscience to archaeology to the human brain and behavior.