This exhibit room introduces the history of Lake Biwa. Lake Biwa has its beginnings approximately four million years ago. The sediments and fossils around us can tell us a lot about the lake’s history. Studying them shows that there have been significant changes to Lake Biwa’s environment and climate as well as the flora and fauna that made the area their habitat.
Lake Biwa is surrounded by mountains. If you were to look around you from the middle of the lake, you would see mountains in all directions. This zone introduces the various rocks found around Lake Biwa. Mount Hiei, Mount Hira and other mountains to the west of Lake Biwa are made of hard rock. The current landscape of Lake Biwa, surrounded by tall mountains, was created over a very long span of time. The rocks that comprise the mountains also have their respective histories, such as being formed at the bottom of the ocean or by volcanoes, before becoming mountains.
There are no elephants in the forests of Japan today. However, about 1.8 million years ago, a small species of elephant, called the Akebono elephant (Stegodon aurorae), used to roam the area. The Akebono elephant later became extinct. However, the nearly complete fossilized remains of an Akebono elephant were found in Shiga Prefecture’s Taga Town. This diorama was created by reconstructing forest and lake scenery based on information gained through fossilized plants and geographical strata. Metasequoia, Chinese swamp cypress, and other trees that are now extinct in Japan, grew in the forests at that time.
Stegodon miensis, which had a height of nearly four meters, lived about four million years ago in the area around Lake Biwa. It was a species close to Stegodon zdanskyi, which inhabited China at the time. It seems that the Mie elephant was slightly smaller. This is a replica of skeletal specimen of a Stegodon zdanskyi. The left half is a reconstruction of a living Stegodon zdanskyi. After making its way to Japan, these elephants evolved into the Mie elephant, which in turn evolved into the small-sized Akebono elephant.
Lake Biwa has its beginnings as a lake that existed four million years ago in Iga City, Mie Prefecture. The lake changed its location about once every several hundred thousand years. It expanded to its current location about four hundred thousand years ago. At this exhibit, you can watch an animation to see how the lake changed over time. The lake moved its location due to changes in the terrain that transformed where water collected or where mountains were located. Changes in the terrain are related to the movement of faults that cause earthquakes.
A survey of the sediment layer is carried out to understand the history of Lake Biwa. The Kobiwako Group composed of sedimentary layers are located in the hills that start from the Lake Biwa area to the vicinity of Iga City in Mie Prefecture. Studying the sediments helped us start to understand in what kind of an environment Lake Biwa existed in the past. The sediments that go back more than a million years can be found below Lake Biwa. If it were possible to remove the strata entirely, we would see the shape of the mountain that existed before the lake was formed. The sediments at the bottom of the lake and the terrain below them offer clues on how the lake as it is today was formed.
Several million years ago, there were crocodiles in the vicinity of Lake Biwa. This is evident from their footprints, fossilized teeth and other evidence found in the Kobiwako Group composed of the sediments. This exhibit shows a replica of a footprint from about 3.7 million years ago, and a reconstructed two-meter-long crocodile. During this period, there were large animals like elephants and rhinoceroses around Lake Biwa. Fossils and research on the DNA of current animals show that the animals around Lake Biwa became extinct or evolved over a very long span of time.
Fossils of leaves, seeds, stems and other parts of plants are left by flora. Even pollen, which can be viewed through a microscope, can become fossils. The fossils of plants can tell us about the vegetation that grew around Lake Biwa in the past. The trees in the forests and plants came and went, changing as time passed. One of the reasons for this was global climate change. Based on a study of fossilized pollen, it seems that twenty-thousand years ago, the area around Lake Biwa was colder than northern Hokkaido, Japan’s northernmost island. At this zone, you can experience what summer and winter temperatures were like twenty-thousand years ago.
Lake Biwa’s history goes back about four million years. During that time, there were periods when the climate was warm, followed by periods of cold, after which it eventually became cold overall. Fossilized plants indicate that the type of plants that grew in the area changed according to the changes in the climate. This exhibit is the fossilized root of a tree that grew about 1.8 million years ago. Many fossils of a tree called Metasequoia from this period have been found. However, there were no Metasequoia fossils starting from around eight hundred thousand years ago. It indicates that this tree became extinct in Japan.
This exhibition room introduced changes in the natural environment of Lake Biwa, such as the landscape, climate and wildlife, during the lake’s history of about four million years. Researching the sediments and rocks beneath our feet as well as fossils have helped us learn about the changes in the natural environment surrounding Lake Biwa. Many of such specimens were collected by the citizens who were not scientists. Rather, they were collected out of interest by different people of the community. You, too, might discover new things if you study the things found around you.