If you ask a geochemist, they might say that most of Earth’s carbon should have been burned off during the formation of the Earth or was chemically locked up in the core of our planet about 4.5 to 5 billion years ago. So where then did all the carbon that living organisms are built of come from? It turns out that most of the carbon we use today came from a collision with another smallish planet about 4.4 billion years ago.
Scientific Article:li etal 2016
marchi etal 2106