Context: The age of the Earth is about 4.54 billion years old. The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago, during the Eoarchean Era after a geological crust started to solidify following the earlier molten Hadean Eon. There are microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia. Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old metasedimentary rocks discovered in Western Greenland. More recently, in 2015, "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia. According to one of the researchers, "If life arose relatively quickly on Earth ... then it could be common in the universe."

Question: What is the estimate age of the Earth?
Answer: about 4.54 billion years old

Question: What era contains the earliest undisputed evidence of life on Earth?
Answer: the Eoarchean Era

Question: What is the name of the era that predated life on Earth?
Answer: Hadean Eon

Question: Where were the billion year old microbial mat fossils found?
Answer: Western Australia

Question: Where were the 3.7 billion-year-old metasedimentary rocks discovered?
Answer: Western Greenland

Question: What is the estimate age of rocks?
Answer: Unanswerable

Question: What era contains the earliest undisputed evidence of rocks on Earth?
Answer: Unanswerable

Question: What is the name of the era that predated rocks on Earth?
Answer: Unanswerable

Question: Where was the 4.54 billion year old graphite found?
Answer: Unanswerable

Question: Where were the 3.7 billion year old fossils found?
Answer: Unanswerable