Is life from Earth scattered all over our Milky Way?

The asteroid that killed the dinosaurs would have thrown billions of tonnes of rock and water out into space. Credit: NASA

A team of scientists from Japan are suggesting that the asteroid impact that killed dinosaurs may have also spread life from Earth throughout our Milky Way.
 
65 million years ago, a 10km-wide asteroid smashed into the Earth and brought the 165 million-year reign of the dinosaurs to an end.

It also spewed billions of tonnes of (potentially) life-bearing rock out into space. The Japanese team of physicists believe they have calculated what happened to it all.

The immediate effects of a trillion-tonne rock smashing to the Earth are well documented, global wildfires, mega-tsunamis and mass extinctions, but the impact would have also thrown out billions of tonnes of water and rock that could have carried microbial life with it.

Researchers from Kyoto Sangyo University, in Japan believe they know where some of these rocks went.


They have focused their efforts on the chunks of rock that may have landed in areas of the galaxy where life could potentially prosper.

On the shortlist were moons and planets thought to possess water, such as Jupiter’s moon, Europa; Saturn’s moon, Enceladus and Earth-like exoplanets orbiting other stars.

Surprisingly, they have calculated that almost as much ejecta (rock and ice) would have landed on Enceladus as on the Moon – around a hundred million individual rocks.

But the largest proportion of these rocks are thought to have ended up interstellar space.

The team has estimated that about 1,000 pieces of “Earth rock” would have reached the red dwarf star, Gliese 581, where at least six planets have been identified as candidates for life.

Gliese 581 is located 20.3 light years from Earth, so it would have taken the rocks about a million years to make the journey.

Scientists don’t know if microbial life could survive such an extended journey through the cold vacuum of space, but the possibility that some sort of life from Earth could have made its home there is something the paper considers.

Based on this premise, the team have calculated how long it would take for ejecta from Earth to seed the entire galaxy with life.

They suggest that it would take about a trillion years (1,000 billion) to spread through a volume of space the size of our Milky Way. Well, it is only 10-13 billion years old.

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What is intriguing is that amino acids in several meteorites show enantiomeric excesses of the same handedness as that seen in biological amino acids. Therefore, the process that produced the handedness of amino acids in the meteorites may provide clues to how homochirality developed in life forms on Earth. The larger question becomes how enantiomeric excesses can be produced and under what conditions.

How did life on Earth begin? One hypothesis is that terrestrial life began when organics were delivered from outer space during the early, heavy bombardment phase of Earth's development. We know that several meteorites (e.g., Murchison) have amino acids with properties similar to those seen in biological amino acids, the building blocks of life.

An international team of astronomers led by Fukue and Tamura of the National Astronomical Observatory of Japan conducted research on the properties of light in a massive star-forming region (BN/KL nebula) of the Orion Nebula and have investigated a process that may have played a role in the development of life on Earth.

The origin of what is technically called "biomolecular homochirality" is a longstanding mystery and an important one to solve, since it characterizes most life forms on Earth.

Chirality refers to the handedness of an image or phenomenon, which is not identical to the mirror image of its counterpart, much as the right and left hands are similar in structure but are opposites and thus not the same.

Homochirality means that a group of molecules exhibit the same handedness. Therefore, biomolecular homochirality indicates an organic group of molecules that are characterized by the same handedness. Terrestrial living material displays homochirality and consists almost exclusively of one enantiomer, L-amino acid, one of a pair of amino acids.

What is intriguing is that amino acids in several meteorites show enantiomeric excesses of the same handedness as that seen in biological amino acids. Therefore, the process that produced the handedness of amino acids in the meteorites may provide clues to how homochirality developed in life forms on Earth. The larger question becomes how enantiomeric excesses can be produced and under what conditions.