Did Comets Make Life on Earth Possible?

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Most scientists have long believed that life on Earth began as a "primordial soup" in a lake or pond some four billion years ago. According to this theory, chemicals from the atmosphere combined with some form of energy necessary to make amino acids—the building blocks of proteins—to create the first primitive organisms, kicking off the evolution of Earth's species.

But the primordial soup theory is being increasingly disputed. Many geophysicists now say the Earth did not have enough gases, like ammonia and methane, from which organic material like amino acids could be produced.

Instead, a growing cadre of scientists believes the organic material needed to create life may not have been produced on Earth, but was instead brought here by comets. The newly formed Earth was likely subjected to a fierce bombardment of comets four billion years ago. These comets may have brought with them the organic compounds that later evolved into living matter.

According to the most radical theory, known as "panspermia," life in a ready-made form is ubiquitous in the galaxy and is brought by comets to new planets. Few scientists subscribe to this hypothesis, however.

Perhaps the main question is whether organic molecules can survive space travel or if they break up and contribute the atoms that are necessary to ultimately make biological material and water?

"Our museums contain examples of primitive meteorites that likely are very similar to the material delivered by comets," said Mumma. "The key point is that small bodies deliver their organics intact to Earth's surface. This must have been a common event on the early Earth."

Many scientists are now leaning toward a combination of the comet impact theory and the primordial soup thesis. Some chemical building blocks may have come from comets, but the assembly into life took place on Earth.

"The comet impact theory fits in with the primordial soup theory," Mumma said. "They can be complimentary."

Drilling Into Comets

Scientists will measure the molecular make-up of comets to better understand what chemical reactions formed them. This may provide clues to the evolution of carbon-based chemistry on Earth in its early history.

The new research will combine laboratory experiments, observations with telescopes and spacecraft, and missions to sample comet and asteroid material. A European mission not associated with NASA is even going to land on a comet and drill into it as the comet journeys toward the sun.

An important part of the project will focus on water, which is seen as an essential ingredient of life. Scientists want to know if the Earth's water was incorporated into the Earth as the planet formed or if the water arrived on Earth as a result of cometary impacts after the Earth was already formed.

"Earth's new oceans were filthy, and should have been full of organic molecules and dust particles carried to our planet by comets and primitive meteorites," said Mumma. "We want to learn how significant their contribution was to the genesis of life on Earth."

The comet research could have a tremendous impact on the quest to find life on other planets. After all, comets have slammed into many other planets. If they supplied the raw material to form life on Earth, what is to say the same thing hasn't happened on other planets?

One thing is for sure, however. Finding out exactly how life on Earth began, and if it extends elsewhere, will take some time. The first stage of the NASA project will last five years, but Mumma thinks it could take as much as 25 years before scientists have a definite answer about the origin of life on Earth.

National Geographic Resources on Comets and Asteroids

News Stories:
Far-Out Theory Ties SARS Origins to Comet
Comets: How Big A Threat To Earth?
Surprise Comet Streaks Into Solar System
Comets May Have Led to Birth and Death of Dinosaur Era
Pluto: Planet or Comet?

Killer Asteroids: A Real But Remote Risk?
Is a Large Asteroid Headed for Impact With Earth in 2880?
Fires From Asteroid May Have Spared Some Regions
"Dinosaur-Killer" Asteroid Crater Imaged for First Time
Prehistoric Asteroid "Killed Everything"
Mass Extinction That Led to Age of Dinosaurs Was Swift, Study Shows
Researchers Rethink Dinosaur Die Off Scenario
Chesapeake Bay Crater Offers Clues to Ancient Cataclysm
Fossil Leaves Suggest Asteroid Killed Dinosaurs
U.S. Summons Experts to Draft Asteroid Defense Plan
NASA Should Lead Asteroid Defense, Group Says
NASA Practices Satellite Flyby of Asteroid
Fighter Jet Hunts for "Vulcanoid" Asteroids

Universe Reborn Endlessly in New Model of the Cosmos
First Evidence for Early Meteorite Bombardment of Earth
Unusually Well Preserved Crater Found in North Sea
What Caused Argentina's Mystery Craters?
Moon Derives From Earth, Space Object, Study Says
Was Moon Born From Planet's Crash Into Earth?

Leonid Meteor Shower Most "Spectacular" for Decades
Researchers Harvest the Spoils of Chicago Meteor Shower
Astrophysicist Recognized for Discovery of Solar Wind

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