Lunar mare
Neolithic stones in Ireland hold the earliest known drawings of the Moon surface. These carvings predate written history by thousands of years. During China's Warring States period, poems described dark marks on the Moon as a Rabbit. Ancient Greek philosophers like Thales and Democritus believed the Moon was rocky and earth-like. They argued there were no seas on its surface. Roman historian Pliny the Elder used the word mascula to describe lunar spots. He thought the Moon was covered in mud rather than water. Plutarch wrote about the Moon between 46 and 120 AD. He compared Caspia to the Caspian Sea on Earth. This comparison helped fuel ideas that the Moon held actual bodies of water.
William Gilbert published his new philosophy about the sublunar world around 1600. His work remained private until 1654. Thomas Harriot became the first person to use a telescope for Moon observations in 1609. He created a detailed map in 1611 but kept it secret. Galileo Galilei released Sidereus Nuncius in 1610 with his own findings. He described the surface as rocky and found no evidence of water. Johannes Kepler changed his mind after reading Galileo's account. Giovanni Battista Riccioli produced an accurate map in 1651 titled Almagestus. His naming system remains in use today. Christopher Wren built a lunar globe in 1661 showing cavities and eminences. Robert Hooke linked these features to volcanism in his 1665 book Micrographia.
Radiometric dating places mare basalts between 3.16 and 4.2 billion years old. Crater counting methods suggest some flows are as young as 1.2 billion years. Samples from the Chang'e-5 mission show basalt could be only 2.03 billion years old. Most eruptions occurred between 3 and 3.5 billion years ago. Volcanic activity on the far side is much older than near-side flows. Youngest lava exists within Oceanus Procellarum on the nearside. Initial volcanism began within 100 million years of basin formation. Many basalts flowed into low-lying impact basins. The largest volcanic unit, Oceanus Procellarum, does not match any known impact basin.
Mare basalts cover about 16% of the lunar surface. They appear mostly on the side visible from Earth. Far side maria are smaller and reside inside large craters. Gravity fields do not explain why eruptions favor one hemisphere. Centrifugal acceleration equals gravitational pull in a rotating frame. No net force directs magma toward Earth. Tidal forces create an elongated ellipsoid shape with high points at both poles. Crustal thickness alone cannot control where lavas reach the surface. The South Pole-Aitken basin has the lowest elevations yet remains sparse. Data from the Lunar Prospector mission shows heat-producing elements concentrate in Oceanus Procellarum. This unique geochemical province is called the Procellarum KREEP Terrane.
All mare basalts classify as tholeiitic under terrestrial schemes. Scientists group them by major element chemistry into three series. High-Ti basalts contain up to 15 weight percent titanium dioxide. Most terrestrial basalts have less than 4 weight percent titanium. Very-low-Ti groups exist but are rare. A special category called KREEP basalts holds potassium, rare-earth elements, and phosphorus. Lunar rocks lack hydrogen-bearing minerals like amphiboles. Water exists in near-total absence within these samples. Terrestrial basalts often show alteration or metamorphism through water interaction. Global remote sensing data reveals a continuum of titanium concentrations. High-titanium concentrations represent the least abundant group among all samples.
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Common questions
What is the age of lunar mare basalts according to radiometric dating?
Radiometric dating places mare basalts between 3.16 and 4.2 billion years old. Some flows from the Chang'e-5 mission show basalt could be only 2.03 billion years old. Most eruptions occurred between 3 and 3.5 billion years ago.
Who was the first person to use a telescope for Moon observations in 1609?
Thomas Harriot became the first person to use a telescope for Moon observations in 1609. He created a detailed map in 1611 but kept it secret. Galileo Galilei released Sidereus Nuncius in 1610 with his own findings.
Why do lunar maria appear mostly on the side visible from Earth?
Mare basalts cover about 16% of the lunar surface and appear mostly on the side visible from Earth. Data from the Lunar Prospector mission shows heat-producing elements concentrate in Oceanus Procellarum. This unique geochemical province is called the Procellarum KREEP Terrane.
What did ancient Greek philosophers believe about the Moon's surface before telescopes existed?
Ancient Greek philosophers like Thales and Democritus believed the Moon was rocky and earth-like. They argued there were no seas on its surface. Roman historian Pliny the Elder used the word mascula to describe lunar spots and thought the Moon was covered in mud rather than water.
How many series of mare basalts exist based on major element chemistry?
Scientists group them by major element chemistry into three series. High-Ti basalts contain up to 15 weight percent titanium dioxide. Very-low-Ti groups exist but are rare.