First evidence of abundant fossils?

Ever since recorded history began, and probably before, people have found fossils, pieces of rock and minerals which have replaced the remains of biologic organisms or preserved their external form. These fossils, and the totality of their occurrence within the sequence of Earth's rock strata is referred to as the fossil record.

Carbon-14

The first method was invented by Williard Libby in the 1950s. He discovered that radiocarbon, C-14, had a half life of nearly 6000 years. (The actual number is closer to 5730 years)

The world's oldest terrestrial material, a tiny grain of zircon crystal whose study radically altered scientific views of the early Earth, will be on brief public display Saturday, April 9, at the Geology Museum.

Measuring little more than two human hairs in diameter, the tiny grain of zircon crystal was found in the Jack Hills region of Australia and is estimated at 4.4 billion years old. It was dated by Simon Wilde, a professor in the School of Applied Geology at Curtin University of Technology in Perth, Western Australia.

Thousands of meteorites, which are fragments of asteroids that fall to Earth, have been recovered. These primitive objects provide the best ages for the time of formation of the Solar System. There are more than 70 meteorites, of different types, whose ages have been measured using radiometric dating techniques. The results show that the meteorites, and therefore the Solar System, formed between 4.53 and 4.58 billion years ago. The best age for the Earth comes not from dating individual rocks but by considering the Earth and meteorites as part of the same evolving system in which the isotopic composition of lead, specifically the ratio of lead-207 to lead-206 changes over time owing to the decay of radioactive uranium-235 and uranium-238, respectively. Scientists have used this approach to determine the time required for the isotopes in the Earth's oldest lead ores, of which there are only a few, to evolve from its primordial composition, as measured in uranium-free phases of iron meteorites, to its compositions at the time these lead ores separated from their mantle reservoirs. These calculations result in an age for the Earth and meteorites, and hence the Solar System, of 4.54 billion years with an uncertainty of less than 1 percent. To be precise, this age represents the last time that lead isotopes were homogeneous througout the inner Solar System and the time that lead and uranium was incorporated into the solid bodies of the Solar System.

Fossils: base of the Cambrian Period (the "Cambrian Explosion"), around 600 Ma.

Oldest dated rock: Ur-ages from zircons, around 3.8 Ga.

Age of the Earth: around 4.6 Ga.

PRE CAMBRIAN AND THE CAMBRIAN ....MARINE LIFE LIKE TRILOBITES AND SUCH