Suavjärvi is a lake and impact crater in the Republic of Karelia, Russia about 50 km north of the town of Medvezhyegorsk. The approximately 3 km wide Suavjärvi lake is located in the centre of the crater. The crater is 16 km in diameter and it is estimated to be about 2.4 billion (2.4 x 109) years old, placing it in the Archean–Proterozoic boundary. That makes it the oldest known impact crater on Earth. Not much of the crater has survived, although some shock features like large blocks composed of impact breccia have been found.
The Suavjärvi structure is situated within the Karelian craton, which is the oldest (Neoarchean) stable domain of the Fennoscandian Shield (Lobach-Zhuchenko et al. 1986; Rundquist and Mitrophanov 1993; Mints et al. 2009; and references therein). The basement of the craton is a late Archean (Lopian) granite-greenstone terrane consisting of granitoid-gneiss complexes and supracrustal rocks ranging in age between 3.14 and 2.62 Ga. Supracrustal metavolcanic-sedimentary rocks form north-trending greenstone belts, surrounded by spatially more extensive granitoids and higher grade gneiss domains.
Popigai crater is the site of one of the largest diamond fields in the world today, estimated to contain “trillions of carats.” Because they were formed instantly, the “impact diamonds” did not have time to develop as large, single gemstones. Most are polycrystalline stones smaller than two millimeters and with low purity, making them better for industrial uses than for jewelry.
About 36 million years ago, an asteroid slammed into northern Siberia and created one of the largest craters on Earth. Streaking in at an estimated speed of 20 kilometers (12 miles) per second, the asteroid made an impact that ejected millions of metric tons of material into the air. The asteroid—between 5 and 8 kilometers (3 to 5 miles) wide—created a crater nearly 100 kilometers (60 miles) in diameter.
Located about 100 kilometers from the Laptev Sea coast, the round depression dives about 150 to 200 meters (500 to 650 feet) below the surrounding land. Geological mapping and field observations show a central depression at the bottom of the crater, surrounded by a peak ring of about 45 kilometers (30 miles) wide. The ring gradually passes outwards into a ring-shaped trough, which is surrounded by a flat annular terrace.
The crater sits on the northeastern margin of the Anabar shield, which contains a mix of graphite-bearing rocks and sedimentary rocks. The impact from the asteroid melted 1,750 cubic kilometers (420 cubic miles) of rocks and instantly transformed the flakes of graphite into diamonds. Diamonds formed in a hemispherical shell about 1.6 kilometers (a mile) thick and about 12 to 13 kilometers away from the impact site. Scientists estimate that diamonds did not form at the impact site because the collision’s heat and pressure were likely too great to survive there.
On 30 June 1908, the sky above Siberia flared so bright and hot that a witness standing dozens of kilometers from the site thought that his shirt had caught fire, said Vladimir Pariev, co-author of the new Tunguska study and a researcher with the P. N. Lebedev Physical Institute of the Russian Academy of Sciences in Moscow.
Known as the Tunguska event, the blast flattened more than 80 million trees in seconds, over an area spanning nearly 800 square miles (2,000 square kilometers) — but left no crater. A meteor that exploded before hitting the ground was thought by many to be the culprit. However, a comet or asteroid would likely have left behind rocky fragments after blowing up, and no “smoking gun” remnants of a cosmic visitor have ever been found.