Yoshiyuki Suto, from the Nagoya University.

The Hellenistic world, regarded as the earliest age of globalization in human history, was discussed at the conference Articulating Time in the Hellenistic World, given by Yoshiyuki Suto, a professor of Ancient History and academic staff of the Center for the Cultural Heritage and Texts (CHT) at the Nagoya University..

The emergence of a multicultural society has imposed the need to synchronize calendars and to standardize documentary records and the dating of historical events. "The setting of time was closely related to the sense of social stability," said Suto during the Humanities / Social Sciences Workshop of the second phase of the Intercontinental Academia (ICA), on March 10.

"We have agreed on the use of units such as hours, minutes, seconds and days to express time, but we do not think about the origin of these markers."

From the observation of the stars, the Egyptians have been the first to count annual periods and also the pioneers in creating 12 subdivisions of time based on seasons. Greek historian and geographer Herodotus wrote on this ability of the so-called "time masters" in 3 BC. "Their calculations are more accurate than those of the Greeks, who added an intercalary month every two years so that the seasons could coincide. The Egyptians counted 30 days for each of the 12 months, adding five days to the total of each year and thus the full circle of the seasons would coincide with the calendar," Herodotus wrote.

Suto has been specializing in the history of Egypt under the Ptolemaic dinasty. "It is interesting to observe not only the advanced knowledge of the Egyptians, but also the unique feature of that moment. During Hellenism there has been the first era of globalization in human history. The creation of huge empires and the division into large kingdoms features a totally different time in comparison to the previous one," he said.

This period was marked by the expeditions of Alexander the Great to Asia, by the first invasion of Rome in Eastern Greece and by the spread of the Greek language. Public announcements and historical events often needed to be recorded in more than one type of spelling or language, and considering the calendars adopted by different peoples, Suto said. Those were common public documents referencing reigns, bishoprics and other historical facts, accordingly to Sumerian, Egyptian or Greek calendars, to avoid mistakes about the date or the fact that they wanted to portray.

Thus, the time synchronization was necessary. In order to date documents, some important reference points have been used, such as the Trojan War, the Flood of Deucalion (the Greek Noah) or the Return of the Heracleidae. A more explicit time series was created from the Olympic Games in Athens. "The new benchmark was based on the list of Olympic winners," Suto said.

To show how time synchronization evolved between the different peoples of ancient history, Suto introduced two basic concepts related to time in history. The first concept compares progressive time and recurring time, where progressive time is connected to a linear chain of events between past, present and future, and recurring time is caracterized by a repeated cycle of events from period to period, such as celebrations. The second concept compares natural time and human time, where natural time is related to astronomical phenomena and nature, and human time is linked to cultural articulations and a personal interpretation of natural time.

Even in ancient societies, natural time did coincide with celebrations and human needs as harvesting and planting, for example. But it was during the Hellenistic period that the definition of beginning and end of basic chronological units occurred, as well as the synchronization of various human times and ways to denote human time in daily life, he said.

There was no way to articulate a unit of time that had more than one year. Besides, there were difficulties to distinguish one year from another in a chronologically progressive time. Initially, the way that was found to do this was giving the name of a magistrate or an elected priest to a year. "It has certainly avoided a lot of trouble, but it was not practical because these references did not give a sense of relative sequence in relation to the facts," Suto said.

The way to mark time progressed in the Hellenistic kingdoms, especially in the Ptolemaic Egypt, the most successful and enduring of them. An alternative system became better known: to count the year from the throne succession of each king. For example, the year of the coronation of Ptolemy I (305-4 BC) was called the Year I of Ptolemy of Egypt.

The establishment of the concept of regular years has not only contributed to the identification of a given year, but also of longer periods. "It allowed to articulate progressive time with the respective period of each king's domain," he said.

This was demonstrated in a 300-name-long king list graphed over a papyrus. The document, entitled Turin Royal Canon, dates from the time of Ramses II and brings the exact duration of each reign. It is unknown why it is the only list of kings of the Pharaonic period.

Ptolemy II, co-regent of his father, Ptolemy I Soter, introduced changes in the calendar. He tried to extend the year of his reign, considering the period during which he was co-regent. "The reason for this is unknown but it is believed that it has been an attempt to extend his authority over the legislators of other kingdoms," Suto said.

After all, the regular year system starting from the year in which a new king succeeded the former one resulted in a convenient way to determine the beginning and the end of each period, Suto said. Thus, the striking feature of the Hellenistic phase was not only the structural and cultural integration of the kingdom. There was also the important time synchronization that in previous periods was locally separated in different parts of the kingdom.

Sasaki said that the formation of the Earth and the Moon, 4.5 billion years ago, and the influence of the Moon on the planet are the determinants of the length variation of a day and a month throughout the Earth's history.

Planetary scientist Takanori Sasaki

According to him, the most accepted hypothesis to explain the origin of the Moon is the occurrence of a giant impact between a Mars-sized body and what could be called the proto-Earth.

But when did this impact occur exactly? Sasaki explained that to have this question answered researchers analyze the transformation of the isotope hafnium-182 into the isotope tungsten-182. "Hafnium is a lithophile (rock-loving) element and tungsten is a siderophile (iron-loving) element, respectively connected to the mantle and the core of a star.

According to Sasaki, the giant impact has produced a magma ocean on the proto-Earth, which seems to have lead to a considerable separation between metal and silicates. Thus, the age of the hafnium-tungsten (Hf-W) separation would be the age of the last huge impact, that is, the age of the Earth and the Moon. "It is possible to calculate how much tungsten the mantle has and thus determine the age of the planet." Using this method, it has been concluded that the Earth and the Moon emerged at the beginning of the solar system, 62 million years after the system's rise, 4.5 billion years ago.

The impact has generated a large number of fragments around the Earth, which then regrouped giving rise to the Moon at an orbit just above the Roche limit (minimum distance from the center of the planet that a satellite can orbit without being destroyed by the severity of the tidal forces), said Sasaki. This limit is at a distance of three times the Earth's radius, but now the Moon is at a distance of 60 times the radius size, and should stop to move away when the distance reaches 80 times the radius size, in a multibillion years.

To measure the distance between the Earth and the Moon scientists use time: how long it takes for a laser beam to reach the Moon, be reflected and reach the Earth. The Lunar Laser Ranging Experiment uses this method and the first measurement was made in 1969. With this method, it was decided that the Moon is at 384,400 km from the Earth. Then, the Experiment found a surprising fact: analyzing the data from January 1992 to April 2001, the researchers found that the Moon is moving away 3.8 cm per year. "If this is correct, then the Moon was much closer in the past," Sasaki said.

There is an exchange of angular momentum between the Moon and the Earth. Sasaki cited a hypothesis that is mentioned in the reference book of this area, "Solar System Dynamics," by Carl Murray and Stanley Dermott: "It is highly likely that the orbit of the Moon and the Earth's rotation have considerably changed during the existence of the solar system, especially due to the action of semidiurnal tides [when the Moon is over a location on the Earth and then on its opposite side] caused by the Moon to the Earth."

This means that the Moon attracts the mass of water and this reduces the speed of the Earth's rotation. At the same time, the tide shifting due to the Earth's rotation attracts the Moon, gaining angular momentum and gradually distancing. The Moon also gets slower, reducing the duration of the month.

Sasaki explained that according to the Kepler's 3rd Law (the square of the orbital period of a planet is directly proportional to the cube of half the major axis of its orbit), the closer to the Sun, the higher the speed of a planet, and the further away, the slower. This also applies to the Moon-Earth system.

An attempt to prove the variation in month length has been made by two researchers that studied the structure of a certain type of sea shell. For Sasaki, "this is a controversial article, but it provides some interesting directions." The shells develop lines of daily growth in segments with monthly growth. Analyzing shells today, it appears that they have 30 rows per segment, which means a 30-day month. "In fossil shells of 400 million years ago there are only 9 lines per segment, assuming that the month lasted 9 days. This indicates that the Moon spun faster around the Earth and at a distance 40% smaller than the current one."

After all, how long did a day last when the Earth and the Moon came to be? "At first, the Moon was at a distance of three times the Earth's radius, immediately after the Roche limit. With this distance and the estimated angular momentum, it can be said that the day lasted only 4 hours. Over time, the Moon moved away and the length of the day increased: when the planet and its satellite were 30,000 years old, the day lasted six hours; when they were 60 million years old, the day lasted 10 hours."

At the end of his presentation, Sasaki presented a graph relating the development of life ("though not an expert on the issue") with the length of the day through time. According to it, the first evidence of life, 3.5 billion years ago, happened when the day lasted 12 hours. The emergence of photosynthesis, 2.5 billion years ago, happened when the day lasted 18 hours. 1.7 billion years ago the day was 21 hours long and the eukaryotic cells emerged. The multicellular life began when the day lasted 23 hours, 1.2 billion years ago. The first human ancestors arose 4 million years ago, when the day was already very close to 24 hours long.