And we know from chronologies found elsewhere in the Bible that Abraham lived about 2, years before the birth of Jesus Christ. Summing these lengths of time, we get about 6, years technically just a little more. They rely on radiometric dating, though the story is a bit more complicated than it sounds. Some rocks contain trace amounts of radioactive atoms. Those radioactive atoms decay into stable atoms over time.
By knowing the decay rate and measuring the amount of both kinds of atoms in a rock, scientists can compute the amount of time it took to produce the stable atoms.
Some assumptions are involved, however. Were some of the stable atoms present in the rock to begin with? Did some of either type of atom leave or enter the rock during the time being measured for decay? To make matters worse, measuring the age of a rock by different kinds of radioactive atoms such as uranium or rubidium often yields very different ages.
There are many examples of such discordant ages. But even if we accept these ages as correct, there are many other assumptions that cause even more problems. The earth is a very dynamic place, with volcanic eruptions and tectonic plate movements that constantly recycle old rocks into new rocks.
When rocks are recycled this way, it is believed that their radiometric dates are reset. Instead, scientists must look to other bodies in the solar system that are less active geologically.
The search for primordial rocks was one of the scientific reasons we sent men to the moon a half-century ago. Scientists thought that since the moon has far less geological activity than the earth, its rocks would be older. He used samples of the Canyon Diablo meteorite that landed about 50, years ago in what is now the US state of Arizona, and using lead-lead dating came up with an estimated age range of 4. Since then, other meteorites have also been used to find the age of Earth.
They are better preserved than even the oldest rocks on Earth, which get broken down and built back up over time through the movement of plate tectonics. The date is somewhat controversial, with some scientists believing 3. Meanwhile, the oldest mineral grains found on Earth, zircons from Western Australia, date back 4. The cooling and solidifying of the planet likely happened quickly on a geologic time scale, on the order of hundreds of thousands to a million years, Carlson said.
But Adam and Eve wouldn't have found Earth hospitable for a very long time. Even at 2. The first evidence for life on Earth may be Australian stromatolites, fossilized bacterial mats that date back 3. More certain fossils peg life's arrival to 2. Modern humans, by contrast, didn't show up until , years ago. Stephanie Pappas is a contributing writer for Live Science covering topics from geoscience to archaeology to the human brain and behavior.
The processes of plate tectonics mean that the Earth is constantly recycling its rock, breaking it down into magma in the interior before pumping it back up to the surface once more. But old rocks do exist, says Reich, and the oldest rock we know is a tiny piece of zircon found in western Australia. The process of figuring out a rock's age often falls to the scientific techniques of radiometric dating , the most famous of which is radiocarbon dating.
This process focuses on the ratio between the number of carbon and carbon isotopes in any once-living being: that ratio indicates how long it's been since that being was alive.
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