oldest fossil
This sample of rock was taken from the Apex Chert, a rock formation in western Australia that is among the oldest and best-preserved rock deposits in the world, in 1982 and was soon found to contain evidence of early life on Earth. A study published by UCLA and UW-Madison scientists in 2017 used sophisticated chemical analysis to confirm the microscopic structures found in the rock are indeed biological, rendering them -- at 3.5 billion years -- the oldest fossils yet found. This is the rock after analysis in the WiscSIMS Laboratory. John Valley, UW-Madison

Researchers discovered the evidence for the earliest form of life on Earth as the science looks forward to find extraterrestrial life. The search for alien life and origin of life on Earth has found new platforms with two significant findings this week, one from ancient fossils of earth and other from the remnants of Cassiopeia A (Cas A), a supernova which has erupted about 300 years ago.

Researchers at the University of California, Los Angeles (UCLA) and the University of Wisconsin-Madison confirmed that the 3.5 billion-year-old fossil discovered in 1982 from Western Australia contains evidence of the earliest life forms on Earth.

The microscopic fossil studied by the team contained 11 microbial specimens from five separate species. The specimens included organisms which belonged to the class of extinct microbial group Archaea and several other currently existing microbes.

The study published in the Proceedings of the National Academy of Sciences showed the links between the chemical compositions of the fossil and the characteristics of life. The study found that the organisms survived on Earth when the planet lacked oxygen.

The discoveries were made from fossils which were collected from the Apex chert deposit of Western Australia. The researchers identified unique cylindrical and filamentous shaped fossil from the region which was subjected to geological processes during the formation of Earth. The region had not undergone any further changes due to tectonic activities.

The research team published the first description of the discovery in 1993 in the journal Science and had later come up with more supporting evidence in 2002. But critics argued that the rocks contained odd minerals which were similar to biological samples.

The team used a secondary ion mass spectrometer (SIMS) known as IMS 1280 at the University of Wisconsin-Madison to identify the carbon composition of the fossils. They identified carbon isotopes which have characteristic features of life and metabolic functions from the sample fossils.

J. William Schopf, professor of paleobiology at UCLA said, "These are primitive, but diverse group of organisms." The researchers said that they could find identities and likely physiological behaviors of the fossil organisms which were locked inside the rock.

The team discovered that the organisms were phototropic bacteria which relied upon the Sun for its energy synthesis. They were species like Archaea, which produced methane and gammaproteobacteria which consumed methane.

Schopf said that studies such as this one indicate life could be common throughout the Universe. Here on Earth, several types of microbes are already present since 3.5 billion years. He stated that "It tells us that life had to have begun substantially earlier, nobody knows how much earlier, and confirms it is not difficult for primitive life to form and evolve into more advanced microorganisms."

John W. Valley, a professor of geosciences at the University of Wisconsin-Madison who was also leading the research said that there was no evidence that life existed 4.3 billion years ago.

The research had been conducted as a part of the Wisconsin Astrobiology Research Consortium which has been funded by NASA Astrobiology Institute to find the origin of life on Earth and through the Universe.

A recent observation by NASA's Chandra Xray telescope found that remnants of a supernova named Cassiopeia A (Cas A) contained all elements present in a DNA, the genetic material of higher life forms. The telescope detected that these elements were ejected into the interstellar space and further to different planetary bodies. These elements too could be a causal agent for life on different planets, moons or asteroids or other planetary bodies.

Several theories state that life might have formed on Earth or was brought to the Earth following series of meteor showers. Scientists claim that meteorites and space dust contains elements which can build chemical structures of life.