Mountain-size chunks of rock began to coalesce from interstellar dust in our solar system more than 4.5 billion years ago, initiating the process that resulted in the creation of the planets we know today, researchers have determined.

Researchers at the University of California at Davis arrived at the figure of 4.5 billion years, give or take 2 million years, by analysing meteorites known as carbonaceous chondrites, which are made up of the oldest known material left from the formation of the solar system.

The chondrites contain globules of silica and grains of metals embedded in a black mix of interstellar dust that is rich in organic matter. The researchers used what they found to be the consistent ratio of the amount of manganese and chromium isotopes in the meteorites that they studied to determine their age, and, consequently, of that early phase in the formation of the solar system.

The meteorites were too small to heat up from radioactive decay and, thus, never melted as larger structures did, said assistant professor of geology Qing-zhu Yin. As a result, they are considered "cosmic sediments."
"We've captured a moment in history when this material got packed together," he said.

Scientists think that in the second stage of the solar system's development, the mountain-size rocks coalesced into about 20 planets the size of Mars, and that in the third, these smaller planets crashed into each other and created the planets we know today. But the earliest stage has not been well understood, Yin said, making information about when it may have occurred particularly important.

The Washington Post