Modern scientists believe the universe has been around for 13.8 billion years, the sun for 4.57 billion years, the earth for 4.56 billion years and the moon for 4.53 billion years. Anatomically modern humans however only occupy the last 340,000 years of that story of cosmogony and originated out of Africa. Homo erectus (bipedal Humans) are believed to have walked the earth for 1.8 million years. Much of human history is therefore before writing. In some circles although 1.8 million years of human history is most of human history, it is called prehistory.
To understand the pre-history of Africa, we need to understand the language of archaeologists, geologists and geneticists. See archaeological periods article for how archaeologists describe historic time periods and the strengths and weaknesses of their methods. To understand the time scales of African history, in this article we explain the language of geologists.
Over time, several measures, concepts and calendars have been used to describe times and periods. They include:
Concepts of time
Before present is a time scale used mainly in scientific fields (by paleontologists, geologists and archaeological) to denote events that occurred in the past before the 1950s, the year set as the original year before present scale. BP was a scale also used for radiocarbon dating.
Current Era or sometimes called Common Era is a system of notation popularly used in the Gregorian Calendar as a standard calendar. Sometimes, CE can be equivalent to AD because this correspondence was used during the Dinosyian system. 2000CE is equivalent to AD2000.
Before the Common Era like the CE is a notation system used as a standard calendar during the Gregorian era. BCE also corresponded to BC in the Dinosyian System of the calendar. 10 BCE is equivalent to 10 BC.
Anno Domini calendar is based on the conception of Jesus Christmas and follows immediately after the countdown to 1 BC.
MYA (or Ma)
Mya is short for millions of years ago.
Lunar Calendar is a calendar based on the orbit of the moon around the earth after 29 to 30 days. The different phases of the moon signify the time of an occurrence. Using the lunar calendar gives rise to more years during a similar time period as the Gregorian calendar.
A solar is a calendar whose dates is based upon the complete orbit of the Sun by the earth, the position of the earth in relation to the Sun. This system was first developed in Africa with 12 months; each with 3 weeks and 10 days per week in each month, followed by five epagomenal days. The original system had three seasons each covering 120 days.
The addition of an extra day every four years to the 365-day calendar is what we now called the Gregorian Calendar, which is widely accepted as standard and widely used throughout the world. While the Gregorian Calendar used 365.25 days each year on average, with the benefit of the latest knowledge, the most accurate measurement of time span of the earth’s orbit around the sun is 365.256 days per year.
The difference between the Gregorian calendar and the Egyptian civil calendar over 4,582 modern years was 1,145.5 days, equivalent to being 3 years and 50 days out.
Most populations prior to adopting the solar calendar used a lunar calendar which had 354 days on average (12 multiplied by 29.5 days). This gave rise to a deficit of eleven and a quarter days (11.25 days). Over 4,582 years (3000 + 1582), this created a difference of 51,547.5 days, equivalent to being 141.1 years out under the Gregorian calendar.
If a generation is for instance every 32 years for men, the equivalent difference between the lunar calendar and Gregorian calendar is to 4 generations. A 20-year generation would give rise to a difference over 4,582 years of 7 generations. Most populations in Eurasia before adopting a reformed Egyptian calendar introduced by Julius Caesar, used the lunar calendar or worse had calendars with bigger differences to the Solar calendar such as 61 days under the Roman calendar’s 304 days.
The Stellar Calendar
This calendar has 364 days and an extra day after every 72 years which is also known as a leap year. The stellar calendar is based on the position of the Sun in the twelve zodiac signs.
The modern-day calendar is the most widely used calendar presently. The calendar is determined by the earth’s orbit around the Sun. The formation of modern-day calendar dates back to Pope Gregory XIII who re-invented the number of days in each month of the 365 calendar and added leap years in 1582 because the Julian calendar was eleven minutes late. Hence, the Gregorian Calendar was named after him.
Paleoclimatology is the study of the apparent changes in the climate at a particular time especially ancient geological Periods. Paleoclimatology makes use of proxies to find about temperature readings and other records. These proxies can be forams, diatoms, etc. and are used to interpret paleoclimate. Since it was practically impossible to travel back in time to have a first-hand review of events, these proxies were used to estimate the climate difference of the past and present.
The chart shows a geological temperature of different periods and also that these temperatures were irregularly patterned till the Pleistocene period which achieved stability. The high temperature continued to fluctuate due to four contributing factors: the composition of the earth, the continuous inhabitation of the earth, evolution of mammals, and continuous heating of the earth crust. As the earth was adjusting to the fullness of human capacity, his activities and others, temperature stability achieved a downturn until it rose to a stable temperature in the Holocene epoch.
Geological periods are divided into various groupings.
This is the earliest part of Earth’s history. This period preceded the Cambrian. The Cambrian period is name for the period between 541 Ma (the end of the Ediacaran) and 485 Ma (the beginning of the Ordovician Period). It is the first geological period of the Paleozoic Era and the Phanerozoic Eon.
A geological time period used to characterize the Precambrian period. A supereon consists of multiple eons that signify several billion years.
An eon is a very long period of time. An eon can be a billion years. Eons make up a supereon.
A Era is a geological period that spans tens of millions of years and sub-divides Eons.
Cenzoic signifies the most current and recent Era. A geological period following the Mesozoic Era and extending from million years ago to the present. This period is the age of mammal diversification because many forms of other mammals went into extinction.
This is a geological period occurring from 65 to 25 million years ago from the end of the cretaceous period to the beginning of the Neogene period.
This is a geological time period that began from the end of the Paleogene period to the beginning of the present-day Quaternary period. The Neogene period is divided into two epochs, the miocene and the later Pliocene.
Neogene covers the time between 23.03 Ma and 2.58 Ma. Pliocene is an example of an epoch which further is sub-divided into ages: Piacenzian and Zanclean.
The Piacenzian Age
This is an international time scale after the Zanclean age but before the Gelasian age, covering a length of time between 3.6 ± 0.005 Ma and 2.588 ± 0.005 Ma (million years ago).
This is the most recent and current of the three Cenozoic Era. This period spans 2.58 million years ago to this present. The Quaternary period is divided into two epochs – the Pleistocene and Holocene.
The first epoch of the Quaternary period between the Pliocene and the Holocene and the sixth epoch of the Cenzoic Era. This period began about 2.588 million years ago to 11,700 years and a radiocarbon dating of 10,000 carbon – 14 years Before Present.
Early Pleistocene (the Gelasian Age)
This age is the earliest subdivision of the Quaternary time period. The Gelasian was introduced in 1998 and defined the period of magnetostratigraphy. This is used to date sedimentary rocks and volcanic sequences. This process is used to determine the polarity of Earth’s magnetic field to determine the position of deposits of strata.
Calabrian is a subdivision of the Pleistocene epoch, covering ~1.8 Ma.—781,000 years ago ± 5,000 years, a period of ~1.019 million years. This stage was originally defined as an assemblage of mollusk fossils, but after further research by scientists into the type sections of marine water, the Calabrian was redefined as fauna assemblages extended to earlier levels within the Pleistocene. The new type section is now in southern Italy because the initial type section wasn’t viable to use any longer due to insufficient strontium, planktonic foraminifera, and oxygen isotopes.
Middle Pleistocene (Chibanian age)
It’s a subdivision of the Pleistocene epoch between 781,000 to 126,000 years ago. The oldest human DNA is believed to be traced to this period and the transition of human development from the earliest stone age to the middle of Paleolithic.
Late Pleistocene (Tarantian age)
The Late Pleistocene is a geological subdivision of the Pleistocene epoch, covering between 126,000 years ago and 11,700 years ago. This period was denominated by glaciations in North America and the extinction of megafunas (large animals like elephants).
The second epoch in the Quaternary behind the Pleistocene is what we called the Holocene epoch. Holocene is the present-day geological epoch that began around 11,700 years BP. The Holocene period is best defined as Marine Isotope Stage 1 (MIS 1) warm period. This period has seen the continuous evolution of human development, civilization and impacts of humans in the ecosystem.
Meghalaya is the latest age or uppermost stage of the Quaternary period in geological time. It’s also the topmost of the three ages in the Holocene. Its stratotype section point is the Mawmluh cave, one of the deepest and longest caves in India. The condition of the Mawmluh cave was suitable for preserving chemical signs in the transition age, and that accounted for the reason why it became a stratotype section point. The Meghalaya age began in the period where the 4.2 kiloyears extreme climatic event started. This climatic disaster was believed to have started the fall of many kingdoms in Egypt (the old kingdom), Greece, Syria, etc.
Northgrippian is in the middle of the three ages of the Holocene epoch. The Meghalaya was preceded by this age, about (6236 BCE) before the start of the latter.
Greenlandian is the lowest stage and one of the three subdivisions of the Holocene epoch. The stratotype section point is the ice island of Greenland in North America.