Scientists have identified the oldest impact crater known on Earth - and this ancient structure can tell how our planet emerged from the "snowball" phase.
The 70-kilometer-diameter Yarrabubba crater in Western Australia is 2.29 billion years old, plus minus 5 million years, according to a new study. This is about half of the age of the Earth itself and 200 million years more than the age of the previous "record holder" - the impact crater Vredefort, located in South Africa.
The dilapidated Yarrabuba crater was discovered in 2009, but its age has not yet been established.
To date Yarrabubba crater in a new study, scientists led by Timmons Erickson of NASA's Johnson Space Center, USA, studied grains of monazite and zircon minerals sampled from the crater. The authors measured the concentrations of uranium, thorium and lead in these minerals. During crystallization, monazite and zircon actively absorb uranium, but do not absorb lead, while uranium and thorium undergo radioactive decay to lead at known rates. Therefore, the measurements taken in this way allowed the team to figure out the age of the mineral recrystallization event and to reliably establish the age of the crater.
In the work, the researchers also modeled the possible global temperature rise on Earth as a result of this fall of the asteroid, as a result of which it could leave the "snowball" phase, when the entire surface of the planet was covered with a thick layer of ice. The main conclusion from the simulation is that the event under study could cause warming on Earth, but much in this case depends on the composition of the planet's atmosphere in the period under study, about which there is currently only very scant information, the authors explained.
The work was published yesterday, January 21, in the journal Nature Communications.