Error Banner.fade_out.modal_overlay.modal_overlay .modal_wrapper.modal_overlay [email protected](max-width:630px)@media(max-width:630px).modal_overlay .modal_fixed_close.modal_overlay .modal_fixed_close:before.modal_overlay .modal_fixed_close:before.modal_overlay .modal_fixed_close:before.modal_overlay .modal_fixed_close:hover:before. Selector .selector_input_interaction .selector_input. Selector .selector_input_interaction .selector_spinner. Selector .selector_results_container.form_buttons.form_buttons a.form_buttons input[type='submit'].form_buttons .submit_button.form_buttons .submit_button.form_buttons .action_button.hover_menu.hover_menu:before,.hover_menu:after.hover_menu.show_nub:before.hover_menu.show_nub:after.hover_menu.show_nub.white_bg:after.hover_menu .hover_menu_contents.hover_menu.white_bg .hover_menu_contents. “Most zircons on Earth are found in granite, and they formed in the same process that formed the granite.This has led people to assume that all the zircons were reset by impact, so the ages they get from the Moon are impact ages.
Content Wrapper:after.hidden.normal.grid_page.grid_page:before,.grid_page:after.grid_page:after.grid_page h3.grid_page h3 a.grid_page h3 a:hover.grid_page h3 a.action_button.grid_page h3 a.action_button:active.grid_page h3 a.action_button:hover.grid_page h3 a.action_button:not(.fake_disabled):hover.grid_page h3 a.action_button:not(.fake_disabled):focus.grid_pagediv.
Uranium-lead dating from this zircon matched the age of the rocks exposed at Vredefort, not the more recent age of impact (2 billion years). To evaluate the assumption of clock-resetting by impact, Cavosie and colleagues gathered zircons near Earth’s largest impact, located in South Africa and known to have occurred 2 billion years ago.
The Vredefort impact structure is deeply eroded, and approximately 90 kilometres across, says Cavosie, who is also in the Department of Applied Geology at Curtin University in Perth, Australia.
“The original size, estimated at 300 kilometres diameter, is modelled to result from an impactor 14 kilometres in diameter,” he says.
The researchers searched for features within the zircons that are considered evidence of impact, and concluded that most of the ages reflect when the zircons formed in magma.
Did the giant craters on the Moon form during a brief wave or a steady rain of impacts? “The question of what resets the zircon clock has always been very complicated.