The Sangiran dome is located in the central part of Java volcanic island, 12-20 km north of Surakarta city, in the wide sedimentary basin of the Solo axial depression. It is surrounded by the Merapi, Merbabu, and Lawu stratovolcanoes [2]. This eroded anticlinal dome displays about 2.4 million years long history of the area. It pictures the long (and repetitive process of the recession of the sea, deposition in the basin of sediments coming from the rising neighboring hills (Kendeng Hills, Southern Mountains), and also the main phases of volcanic activity (e.g. Gunung, Lawu). Numerous fossils, including Homo erectus, and animals, are found throughout its layers, illustrating dispersals from continental Asia and periods of isolation when Java was separated from the continent by the sea [3][4]. 

Sangiran site covers an area of about 56 km² [5]. Progressively younger units are exposed from the central to the outer part of the dome structure [2]. It is one of the most productive sites in palaeoanthropology, producing more than 100 hominin specimens [6][7].

Sangiran was first investigated by Dutch palaeoanthropologist Eugène Dubois in 1883, but his preliminary fieldwork did not yield many fossils and he eventually shifted his attention to Trinil and East Java where he found the first-ever Homo erectus (then Pithecanthropus erectus) fossils [8]. In 1934, anthropologist Gustav Heinrich Ralph von Koenigswald started to examine the area. And in 1937, he found Sangiran 2, which is a fossilized upper cranium of a Homo erectus (erectus). About more than 100 hominin fossils, including those of the Meganthropus palaeojavanicus have since been found [9][10][11][7].

In 1977, the Indonesian government designated an area of 56 km² around Sangiran as a Protected Cultural Area. A local site museum and conservation laboratory was set up in 1988. In 1996, Sangiran Early man Site became a UNESCO World Heritage Site. And the current museum and visitors’ center was opened on December 15, 2011 [9].

The exposed Plio-pleisocene sediments are divided into four units. The marine Puren (Kalibeng) Formation lies at the base, overlain by the Sangiran (Pucangan) Formation, consisting of shallow marine to lagoonal sediments below lacustrine sediment. The Sangiran Formation is overlain by the Bapang (Kabuh) Formation, and further by the Pohjajar (Notopuro) Formation. The upper two formations are primarily fluviatile sediments intercalated with many layers of pumice, volcanic ash, and lahar [12]. Between the Sangiran and Bapang Formations, a calcified conglomerate called the Grenzbank is frequently found. The majority of the hominid remains are from the Bapang Formation while more archaic fossils were from the Sangiran Formation [13][14].

Dates

Although numerous dating studies have been conducted at this site, the accepted date of the earliest hominin migration is controversial [7]. Systematic investigation of the Sangiran’s chronostratigraphy was first conducted in the late 1970s to early 1990s, including fission-track dating and magnetostratigraphy analysis, which suggested a hominin time span of ~0.8 to 1.1 Ma [15][16] or possibly ~1.3 Ma [17]. However, in 1994 a substantially older ⁴⁰Ar/³⁹Ar date of 1.66 Ma was reported for pumices presumed to overlie the two allegedly oldest hominin remains (Sangiran 27 and 31) [18]. This date has been questioned, but Larick et al. [19] reported a series of hornblende ⁴⁰Ar/³⁹Ar dates that supported the older chronology and placed the Sangiran hominin-bearing sequence from >1.5 to ~1.0 Ma.  The widely cited age of >1.5 Ma derives from a date of 1.51 ± 0.08 Ma [19].

The above dates are divided between two opposing chronological frameworks. The “older” chronology (from between 1.7 and 1.6 Ma to 1 Ma) versus the “younger” chronology (from between 1.3 and 1.1 Ma to between 0.7 and 0.6 Ma) [7]. A recent study using a combination of fission-track and uranium-lead dating points to the earliest presence of  Homo erectus in Sangiran at 1.3 Ma (or <1.5 Ma) [6]. The dates from this study provide important evidence in support of the “younger” chronology. On the other end, the hominid last occurrence at Sangiran is at 0.79 Ma [12].