Section 2

Mission to Collect Materials on the Moon

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Whilst the world watched in excitement as Neil Armstrong and Buzz Aldrin landed on the moon, planetary scientists were focused on something else. For them, the value of the mission was is the cargo they brought back to earth. By the time Armstrong and Aldrin climbed into the lunar module for the last time, they had gathered 22 kilograms of moon rocks, completely filling a small suitcase. Over five Apollo crews brought back a total collection of 382 kilograms of material containing 2,200 samples.

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The rocks were known at the time as a scientific treasure and they did not disappoint. Paul Spudis, a geologist of the Lunar and Planetary Institute in Houston, Texas, said, "Our ideas about planetary formation and evolution must be rewritten after the discoveries made by the Apollo crews." Harold Urey, a Nobel prizewinner, and one of the advocates of lunar exploration had predicted that the moon was composed of primitive meteoritic material. But his conclusion was wrong. Some of the rocks looked just like the rocks on earth.

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Many clues that the lunar rocks contained have taken a couple of years to effectively analyse. Also, some of the conclusions are still debated. A big surprise was the evidence that the early moon was covered by a lot of molten rock. The moon's mountainous regions are made of anorthosite, a rare rock on earth that forms when light, aluminum-rich minerals float to the top of lave.

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Nowadays, the smart money is on the idea that the moon was created as a result of something that occurred around 50 million years after the solar system was created when the Earth was in its infancy. From his hypothesis, the earliest Earth ran into a planet that was a similar size to Mars and debris from the collision went into orbit around the Earth which rapidly came together to form the moon.

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The "giant impact" scenario led to a radical re-evaluation of the history of the early solar system. Before Apollo, planetary scientists watched the collection of objects orbiting the sun like a clockwork mechanism in which collisions were rare and trivial. Now, it is accepted as being a far more active environment, shuffling, colliding or ejecting. This history of all the inner planets has been shaped by collisions and nowhere is that history more visible than the moon.

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Another surprise was the rocks from the moon's largest impact craters indicate that all craters are roughly the same age, between 3.8 and 4 billion years old. It never coincided. The moon and, by extension, the Earth must have been caused by a devastating barrage half a billion years after the solar system formed. To cause this process, something big must have been going back to the outer solar system, but what? Surprisingly, this episode in the history of the solar system has come to be known as the last heavy bombardment and ended at roughly the same time as the first signs of life on earth.

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These key discoveries about our planet's history may never have been made without the samples taken from the moon for chemical analysis and isotopic dating. So, do the Apollo rocks hide any more secrets? All 2,200 samples have been researched, and Randy Korotev, a lunar geochemist at Washington University in St Louis, Missouri, says that it is unlikely that there will be anything groundbreaking left to find from them. However, they may yet keep some more delicate secrets. Korotev says, "We are steadily developing better tools and asking better questions." Especially, the instruments for dating mineral samples have been more delicate, enabling researchers to study the age of ever smaller samples, like tiny mineral grains within a rock.

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These techniques have stimulated a rethink of some key dates in lunar history in the past two years. A team at the Swiss Federal Institute of Technology dated the formation of the moon's magma oceans. Also, by inference, the creation of the moon itself is estimated to have happened between 20 and 30 million years later than we originally thought, at approximately 4.5 billion years ago. Alexander Nemchin with five colleagues in the Cutin University of Technology in Perth, Western Australia also estimated that a lunar zircon was around 4.417 billion years old when the last of the magma oceans solidified.

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The Apollo rock samples are not finished answering some of the bigger picture questions. What will we discover on the opposite side of the moon's surface that we are unable to see from the Earth? Can we put together a detailed history of the lava flows that formed the basalts of the lunar seas? Can we discover any samples from deep inside the moon? These are all seen as very good reasons for coming back to the moon. The big picture needs more samples, more data and more contexts. According to Gary Lofgren, a curator of NASA's lunar rock collection at Johnson Space Centre in Houston, "There's no lack of target and scientific questions. It's not just about the moon but about the solar system's history. This is the lesson that we have learned from Apollo."

Section 3

Organism's Appearance

As Darwin discovered his evolution theory, the earliest known fossils were left in rocks which he called the Silurian age. Older rocks seemed to contain no fossils. The apparently sudden appearance of subtle animals like trilobites was not inconsistent with Darwin's thoughts of gradual evolution. "If my theory will be true, it is unquestionable that before the lowest Silurian stratum was deposited … the world swarmed with living creatures. To the question of why we do not find records of these vast primordial periods, I can give no satisfactory answer," Darwin wrote in the first edition of On the Origin of Species. His puzzle is known as Darwin's dilemma.

Of course, we have discovered a lot of fossils from the earliest periods. Rocks of 3.8 billion years old have signs of life, and the first recognizable bacteria come out in rocks of 3.5 billion years old. During the Ediacaran, approximately one billion years ago, multi-cellular plants with red and green algae appeared and approximately 575 million years ago was found in the first multi-cellular animals.

Even so, there are many perplexing questions. Why did animals evolve so late in the day? And why did the ancestors of modern animals apparently evolve in a geological blink of an eye during the early Cambrian period between 542 and 520 million years ago? Recently, a series of discoveries could help to explain these long-lasting mysteries. These discoveries suggest that the earliest animals evolved much earlier than we thought, perhaps over 850 million years ago. However, the really extraordinary part is that these early animals may have completely changed the planet, paving the way for the larger and more complex animals to follow them.

Several aspects of the biggest discoveries have come from an ancient seabed in China, called the Doushantuo Formation, where unusual conditions conserved some extraordinary fossils. During the last part of the Ediacaran period, layers between 550 and 580 million years old include tiny spheres made of from one to dozens of different cells – just like animals' first embryos. A couple of things have suggested that they are the property of giant bacteria, but a series of studies over the past decade have left little doubt that they are really animal embryos.

Leiming Yin, a researcher at the Nanjing Institute of Geology and Paleontology in China, reported discovering embryos encased inside hard, spiky shells unlike anything produced by bacteria in 2007. Furthermore, evidence of shells that apart from the deficiency of conserved embryos on the inside are identical can be seen in rocks as old as 632 million years – the appearance of the Ediacaran period – suggesting that the animal embryos themselves go back this far.

Other more tentative discoveries push the appearance of animals back even further. Roger Summons, a researcher in the Massachusetts Institute of Technology, and his colleague Gordon Love studies brownish, oily sandstone cores drilled from 4 kilometres below the desert of Oman. The oily remains of dead organisms drifted down to the depths of ancient oceans, where they decomposed slowly because of the lack of oxygen. No visible fossils are present but within that oil are molecular fossils – chemicals taken from the ancient organisms. In layers that are 635 to 713 million years old, Summons and Love discovered 24-isopropylcholestane (24-IPC), a stable form of a kind of cholesterol that these days are only discovered in the cell membranes of certain sponges. "The sponge biomass must have been so substantial," says Love, now at the University of California, Riverside. "They were ecologically outstanding."

Fuel of Life

With the oceans changed, the stage was finally set for the evolution of more complicated body forms. The idea that increasing oxygen levels played a major role in the explosion of life during the Cambrian period is far from new, but most of the researchers attribute the increase in oceanic oxygen to the increase in the atmosphere. If Butterfield is right, it was basically because of animals taking over from bacteria. "These geochemical signatures [of oxygenation] are not causing the evolution of animals," he insists. "They're consequences of the dawn of animals."

"He is right," says Brasier. In fact, he thinks the link between complex life and the transformation of the planet runs even deeper. In Darwin's Lost World, a book published earlier this year, Brasier suggests that the improved burial of carbon resulting from the rising of large cells and groups of cells – perhaps with plants like seaweed – sucked carbon dioxide out of the atmosphere, setting off the series of ice ages that aided the first animals to wrestle for control of the oceans with bacteria. "Rather than being the cause of animal evolution, the ice ages may well have been the response to it," he says.