# data[].attributes.body
How the Earth went from a molten rock to a living planet.

# data[].attributes.attachment_link.readable_text
Life's Rocky Start | Full-Length Broadcast

What is the secret link between rocks and minerals, and every living thing on Earth? This program premiered on January 13, 2016 on PBS.

Four and a half billion years ago, the young Earth was a hellish place-a seething chaos of meteorite impacts, volcanoes belching noxious gases, and lightning flashing through a thin, torrid atmosphere. Then, in a process that has puzzled scientists for decades, life emerged. But how? NOVA joins mineralogist Robert Hazen as he journeys around the globe. From an ancient Moroccan market to the Australian Outback, he advances a startling and counterintuitive idea-that the rocks beneath our feet were not only essential to jump-starting life, but that microbial life helped give birth to hundreds of minerals we know and depend on today. It's a theory of the co-evolution of Earth and life that is reshaping the grand-narrative of our planet's story.

This resource is part of the NOVA: Full-Length Broadcast Collection.

# data[].attributes.attachment_link.title
Life's Rocky Start | Full-Length Broadcast

# data[].attributes.attachment_link.description
What is the secret link between rocks and minerals, and every living thing on Earth? This program premiered on January 13, 2016 on PBS. Four and a half billion years ago, the young Earth was a hellish place-a seething chaos of meteorite impacts, volcanoes belching noxious gases, and lightning flashing through a thin, torrid atmosphere.

# data[].attributes.attachment_link.title
The easiest ways to fix climate change is population control and going vegan - right?

# data[].attributes.body
Current ideas about looking for life on other planets.

# data[].attributes.attachment_link.title
SFI Community Lecture - Chris Kempes - Life on Earth and Beyond

# data[].attributes.attachment_link.readable_text
The moon formed a hundred million years after the creation of the solar system. This has left scientists wondering what was the cause of our planet's satellite to birth if it didn't come from the events that formation of the planets. Here are just three of the most plausible explanations.

Giant impact hypothesis

The prevailing theory supported by the scientific community, the giant impact hypothesis suggests that the moon formed when an object smashed into early Earth. Like the other planets, Earth formed from the leftover cloud of dust and gas orbiting the young sun. The early solar system was a violent place, and a number of bodies were created that never made it to full planetary status. One of these could have crashed into Earth not long after the young planet was created.

Known as Theia, the Mars-sized body collided with Earth, throwing vaporized chunks of the young planet's crust into space. Gravity bound the ejected particles together, creating a moon that is the largest in the solar system in relation to its host planet. This sort of formation would explain why the moon is made up predominantly of lighter elements, making it less dense than Earth - the material that formed it came from the crust, while leaving the planet's rocky core untouched. As the material drew together around what was left of Theia's core, it would have centered near Earth's ecliptic plane, the path the sun travels through the sky, which is where the moon orbits today.

(Image credit: Getty Images )

According to NASA, "When the young Earth and this rogue body collided, the energy involved was 100 million times larger than the much later event believed to have wiped out the dinosaurs."

Although this is the most popular theory, it is not without its challenges. Most models suggest that more than 60%of the moon should be made up of the material from Theia. But rock samples from the Apollo missions suggest otherwise.

"In terms of composition, the Earth and moon are almost twins, their compositions differing by at most few parts in a million," Alessandra Mastrobuono-Battisti, an astrophysicist at the Israel Institute of Technology in Haifa, told Space.com. "This contradiction has cast a long shadow on the giant-impact model."

In 2020 research published in Nature Geoscience, offered an explanation as to why the moon and Earth have such similar composition. Having studied the isotopes of oxygen in the moon rocks brought to Earth from Apollo astronauts, researchers discovered that there is a small difference when compared with Earth rocks. The samples collected from the deep lunar mantle (the layer below the crust) were much heavier than those found on Earth and "have isotopic compositions that are most representative of the proto-lunar impactor 'Theia'", the study authors wrote.

Back in 2017, Israeli researchers proposed an alternative impact theory which suggests that a rain of small debris fell on Earth to create the moon.

"The multiple-impact scenario is a more natural way of explaining the formation of the moon," Raluca Rufu, a researcher at the Weizmann Institute of Science in Israel and lead author of the study, told Space.com. "In the early stages of the solar system, impacts were very abundant; therefore, it is more natural that several common impactors formed the moon, rather than one special one.

Co-formation theory

Moons can also form at the same time as their parent planet. Under such an explanation, gravity would have caused material in the early solar system to draw together at the same time as gravity bound particles together to form Earth. Such a moon would have a very similar composition to the planet, and would explain the moon's present location. However, although Earth and the moon share much of the same material, the moon is much less dense than our planet, which would likely not be the case if both started with the same heavy elements at their core.

In 2012, researcher Robin Canup, of the Southwest Research Institute in Texas, proposed that Earth and the moon formed at the same time when two massive objects five times the size of Mars crashed into each other.

"After colliding, the two similar-sized bodies then re-collided, forming an early Earth surrounded by a disk of material that combined to form the moon," NASA said. "The re-collision and subsequent merger left the two bodies with the similar chemical compositions seen today.

Capture theory

Perhaps Earth's gravity snagged a passing body, as happened with other moons in the solar system, such as the Martian moons of Phobos and Deimos. Under the capture theory, a rocky body formed elsewhere in the solar system could have been drawn into orbit around Earth. The capture theory would explain the differences in the composition of Earth and its moon. However, such orbiters are often oddly shaped, rather than being spherical bodies like the moon. Their paths don't tend to line up with the ecliptic of their parent planet, also unlike the moon.

Although the co-formation theory and the capture theory both explain some elements of the existence of the moon, they leave many questions unanswered. At present, the giant impact hypothesis seems to cover many of these questions, making it the best model to fit the scientific evidence for how the moon was created.

Additional resources

For more on the giant-impact hypothesis, read "The Big Splat, or How Our Moon Came to be: A Violent Natural History"," by Dana Mackenzie. To learn more about the solar system, check out " Our Solar System: An Exploration of Planets, Moons, Asteroids, and Other Mysteries of Space" by Lisa Reichley.

Bibliography

Erick J. Cano et al, "Distinct oxygen isotope compositions of the Earth and Moon", Nature Geoscience, Volume 13, March 2020, https://doi.org/10.1038/s41561-020-0550-0

Raluca Rufu, "A multiple-impact origin for the Moon", Nature Geoscience, Volume 10, January 2017, https://doi.org/10.1038/ngeo2866

Edward Belbruno et al, " Where Did the Moon Come From?", The Astronomical Journal, Volume 129, March 2005.

Thomas S. Kruijer and Gregory Archer, "No 182W evidence for early Moon formation", Nature Geoscience, Volume 14, October 2021, https://doi.org/10.1038/s41561-021-00820-2

# data[].attributes.attachment_link.description
Scientists are still unsure as to how the moon formed, but here are three of their best bets.

# data[].attributes.attachment_link.readable_text
Stokes Crater, pictured here, is one of at least nine craters in the northern lowlands of Mars with exposures of hydrated minerals detected from orbit, according to a June 25, 2010, report.

PASADENA, Calif. -- Minerals in northern Mars craters seen by two orbiters suggest that a phase in Mars' early history with conditions favorable to life occurred globally, not just in the south.

Southern and northern Mars differ in many ways, so the extent to which they shared ancient environments has been open to question.

In recent years, the European Space Agency's Mars Express orbiter and NASA's Mars Reconnaissance Orbiter have found clay minerals that are signatures of a wet environment at thousands of sites in the southern highlands of Mars, where rocks on or near the surface are about four billion years old. Until this week, no sites with those minerals had been reported in the northern lowlands, where younger volcanic activity has buried the older surface more deeply.

French and American researchers report in the journal Science this week that some large craters penetrating younger, overlying rocks in the northern lowlands expose similar mineral clues to ancient wet conditions.

"We can now say that the planet was altered on a global scale by liquid water about four billion years ago," said John Carter of the University of Paris, the report's lead author.

Other types of evidence about liquid water in later epochs on Mars tend to point to shorter durations of wet conditions or water that was more acidic or salty.

The researchers used the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), an instrument on the Mars Reconnaissance Orbiter, to check 91 craters in the northern lowlands. In at least nine, they found clays and clay-like minerals called phyllosilicates, or other hydrated silicates that form in wet environments on the surface or underground.

Earlier observations with the OMEGA spectrometer on Mars Express had tentatively detected phyllosilicates in a few craters of the northern plains, but the deposits are small, and CRISM can make focused observations on smaller areas than OMEGA.

"We needed the better spatial resolution to confirm the identifications," Carter said. "The two instruments have different strengths, so there is a great advantage to using both."

CRISM Principal Investigator Scott Murchie of Johns Hopkins University Applied Physics Laboratory, Laurel, Md., a co-author of the new report, said that the findings aid interpretation of when the wet environments on ancient Mars existed relative to some other important steps in the planet's early history.

The prevailing theory for how the northern part of the planet came to have a much lower elevation than the southern highlands is that a giant object slammed obliquely into northern Mars, turning nearly half of the planet's surface into the solar system's largest impact crater. The new findings suggest that the formation of water-related minerals, and thus at least part of the wet period that may have been most favorable to life, occurred between that early giant impact and the later time when younger sediments formed an overlying mantle.

"That large impact would have eliminated any evidence for the surface environment in the north that preceded the impact," Murchie said. "It must have happened well before the end of the wet period."

The report's other two authors are Francois Poulet and OMEGA Principal Investigator Jean-Pierre Bibring, both of the University of Paris.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for NASA. Johns Hopkins University Applied Physics Laboratory provided and operates CRISM, one of six instruments on that orbiter. For more information about the mission, see http://mars.jpl.nasa.gov/mro/.

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.webster@jpl.nasa.gov

2010-209

Stokes Crater, pictured here, is one of at least nine craters in the northern lowlands of Mars with exposures of hydrated minerals detected from orbit, according to a June 25, 2010, report.

These minerals, including phyllosilicates, have previously been found in thousands of small outcrops in the southern highlands of Mars, but had not...

more

Lyot Crater, pictured here, is one of at least nine craters in the northern lowlands of Mars with exposures of hydrated minerals detected from orbit, according to a June 25, 2010, report.

These minerals, including phyllosilicates, have previously been found in thousands of small outcrops in the southern highlands of Mars, but had not previously...

more

# data[].attributes.attachment_link.title
New Clues Suggest Wet Era on Early Mars was Global - NASA's Mars Exploration Program

# data[].attributes.attachment_link.description
PASADENA, Calif. -- Minerals in northern Mars craters seen by two orbiters suggest that a phase in Mars' early history with conditions favorable to life occurred globally, not just in the south. Southern and northern Mars differ in many ways, so the extent to which they shared ancient environments has been open to question.

# data[].attributes.headline
Neil deGrasse Tyson:  Goldilocks and the Three Planets

# data[].attributes.subject
Neil deGrasse Tyson:  Goldilocks and the Three Planets

# data[].attributes.attachment_link.title
Goldilocks and the Three Planets | Neil deGrasse Tyson

# data[].attributes.attachment_link.description
Earth settled into an orbit with an average distance of 93 million from the Sun. At this distance, Earth intersects a measly one two-billionth of the total energy radiated by the Sun. If you assume that Earth absorbs all incident energy from the Sun, then our home planet's average is about 280 degrees Kelvin (50° F), which falls mid-way between winter and summer temperatures.