Rare space rock holds secret to life on Earth

Time capsule: Minerals and molecules in Aguas Zarcas were forged billions of years ago. © Laurence Garvie

Do meteorites contain the building blocks for life? Scientists have found organic molecules in a 4.5 billion-year-old meteorite, raising the possibility that life came from outer space.

One night last year, a thunderclap made people look outside in Aguas Zarcas, Costa Rica. A blaze of orange and green light streaked across the sky. Dogs barked and children stared as fireballs the size of grapefruit fell on the village, punching holes in roofs and shaking houses.

Tens of thousands of meteorites plunge through the Earth’s atmosphere every year, though humans rarely get to witness their spectacular descent. But Aguas Zarcas (as the rocks became collectively named) was no ordinary meteorite. It was a rare carbonaceous chondrite – older than the Sun, more valuable than gold, and almost alive.

Most meteorites are made of rock and metal, but Aguas Zarcas contains complex organic molecules called amino acids, the building blocks for all life on Earth. A similar meteorite that landed in 1969 in Murchison, Australia, had 100 different types of amino acid.

This discovery is a unique opportunity. Organic compounds are extremely delicate and easily destroyed when exposed to moisture. Preserved in space for billions of years, they can be lost in seconds. Scientists believe this happened with Murchison, but they hope the 30kg of space rock rescued from Aguas Zarcas will provide a pristine glimpse into the past.

Within these rocks are eight billion years of galactic history. The oldest particles of diamond and graphite were ejected from dying stars long before the formation of our own solar system. Then, four billion years ago, the Sun melted this stardust into droplets of molten rock, calcium, and radioactive aluminium.

Over millions of years, these droplets cooled and stuck together to form asteroids, orbiting the Sun between Mars and Jupiter. And, here, they gathered ice and carbon from other rocks as light and heat drove chemical reactions and created complex organic molecules.

But the big question for astrobiology is whether asteroids carry microbial life?

Last November, exciting new research detected sugar ribose in meteorite samples. This is important because ribose forms the “backbone” of RNA, a precursor to DNA. Some scientists are sceptical and say this discovery “makes no sense”. But, if confirmed, it could change our understanding of how life began on Earth.

It first appeared about 3.8 billion years ago and may have been nudged along by meteorites, sprinkling organic compounds into the primordial oceans. But, if this included complex alien proteins and sugars, then life was given – not a nudge – but a huge push in the right direction.

And if life came from space, then scientists expect to find it seeded by meteorites across the galaxy.

We may not have long to wait for answers. In December, samples from the asteroid Ryugu will return for analysis, followed in 2023 by space rock collected on Bennu. Both asteroids resemble Aguas Zarcas but, unlike the meteorite, they have been uncontaminated by the Earth’s atmosphere.

Researchers hope these pristine time capsules will shed more light on the origins of life in the Universe.

So, do meteorites contain the building blocks for life?

We are stardust

Yes, life came from space. We have found all the basic ingredients for life inside meteorites and we know that millions of these rocks have collided with the Earth. So, it is far more likely that life came from space than developed independently on our planet. We tend to assume we are unique, but scientific discoveries continue to reveal that we are not as special as we think.

No, life cannot survive in space. It needs liquid water and an atmosphere to flourish and the radiation in deep space would kill it. This is the big difference between the organic compounds found on space rocks and life itself. Whilst these compounds may be common in the Universe, the climate and environment of Earth are far more important for the evolution of life.

You Decide

  1. Is there life on other planets?
  2. Is it important to understand the origins of life on Earth?

Activities

  1. Draw a diagram of our solar system and include the asteroid belt between Mars and Jupiter.
  2. Use the expert links to research the theory that life came from space. Create a science poster to explain this theory.

Some People Say...

“It really is the most poetic thing I know about physics: you are all stardust.”

Lawrence M Krauss, American-Canadian theoretical physicist and cosmologist

What do you think?

Q & A

What do we know?
Most agree that life needs six chemical elements (oxygen, hydrogen, carbon, nitrogen, sulphur, and phosphorus), liquid water and an energy source to power organic processes. These chemicals form into increasingly more complex molecules, from amino acids to proteins, sugars and, finally, organic life itself.
What do we not know?
Whether these building blocks in meteorites could assemble into microorganisms. Sceptics say we have only found small amounts of these molecules and, in the absence of liquid water, the chemical reactions involved would be very difficult or impossible. However, others point to evidence of higher concentrations of organic molecules in comets.

Word Watch

Aguas Zarcas
Meteorites are named after the place where they land. The size of a washing-machine, Aguas Zarcas broke up above Costa Rica on 23 April 2019. It joined over 60,000 meteorites that have been found and classified by scientists.
Meteorites
Space rocks that fall to Earth are called meteorites and should not be confused with meteors, which burn up in the planet’s atmosphere as “shooting stars”. In space, they are known as meteoroids and are fragments of much larger asteroids and comets.
Carbonaceous chondrite
These rocks resemble lumps of coal, with a sparkling crust that forms as they enter the Earth’s atmosphere. They have a strong earthy smell that some compare to compost, diesel, cooking gas, or Brussels sprouts.
More valuable than gold
The Aguas Zarcas attracted meteorite hunters from all over the world, offering as much as $400 (£305) per gram.
Rescued
By a stroke of luck, the meteorite landed five days before the start of the Costa Rican rainy season. Had it arrived later, the precious organic information would have been lost.
Astrobiology
This field of science combines chemistry, biology, and astronomy to examine the possibility of life in the Universe and the conditions for its development.
Microbial
Microbe is a general term that refers to most microscopic organisms. Microbial describes something relating to a microbe.
RNA
Ribonucleic acid.
Life came from space
The theory that life has been spread throughout the Universe by space rocks and dust is called “panspermia”, from the Ancient Greek pan (all) and sperma (seeded).
Ryugu
The 1km-wide asteroid was named after a magical underwater palace in Japanese folklore.
Bennu
Discovered in 1999, the asteroid was named after an Ancient Egyptian mythological bird.

Subjects

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