June 30, 1908 (Julian calendar/old style: a Tuesday)

The above picture was taken by a Russian expedition to the Tunguska site in 1927, finding trees littering the ground like toothpicks.

On this date, a large rocky asteroid or perhaps an icy comet entered the atmosphere traveling at an estimated speed of about 33,500 miles per hour and then detonated in the sky near the Podkamennaya Tunguska (Stony Tunguska) River in remote Siberia, Russia (60° 54′ 59″ N, 101° 57′ 0″ E). During its quick plunge, the 220-million-pound space asteroid/comet heated the air surrounding it to 44,500 degrees Fahrenheit. At 7:14:28 AM (local Siberia time), at a height of about 28,000 feet, the combination of pressure and heat caused the asteroid/comet to fragment and annihilate itself, producing a fireball and releasing energy equivalent to about 185 Hiroshima bombs. The aerial explosion explains why there was no impact crater – the great majority of the cosmic object was consumed in the explosion.

Reconstruction of the Tunguska Event. (William K. Hartmann)

The massive explosion packed a wallop. The resulting seismic shockwave registered with sensitive barometers as far away as England. Dense clouds formed over the region at high altitudes which reflected sunlight from beyond the horizon. As a result, night skies glowed, and reports came in that people who lived as far away as Asia could read newspapers outdoors as late as midnight. Recent studies of so-called night-shining clouds sometimes linked to space shuttle launches suggest that it was, in fact, a comet that caused Tunguska.

Locally, hundreds of reindeer, the livelihood of local herders, were killed, but there was no direct evidence that any person perished in the blast. Locals believed the blast was a visitation by the god Ogdy, who had cursed the area by smashing trees and killing animals.

Due to the remoteness of the blast and the chaotic conditions prevailing inside Russia at the time, the first scientific expedition to the area would have to wait for 19 years. In 1921, Leonid Kulik, the chief curator for the meteorite collection of the St. Petersburg museum, led an expedition to Tunguska. But the harsh conditions of the Siberian outback thwarted his team’s attempt to reach the area of the blast. In 1927, a new expedition, again lead by Kulik, reached its goal.
____________________________________________________

This is rare, raw footage from the 1921 Tunguska expedition as well as modern day footage showing the aftermath of the huge Tunguska explosion in 1908.
____________________________________________________
While testimonials may have at first been difficult to obtain, there was plenty of evidence lying around. Eight hundred square miles of remote forest had been ripped asunder. Eighty million trees lying on their sides in a radial pattern acted as markers, pointing directly away from the blast’s hypocenter. When the team arrived at ground zero, they found the trees there standing upright – but their limbs and bark had been stripped away. They looked like a forest of telephone poles.

Tunguska Event location (click for larger image).

Such “debranching” requires fast moving shock waves that break off a tree’s branches before the branches can transfer the impact momentum to the tree’s stem. Thirty seven years after the Tunguska Event, branchless trees would be found at the site of another massive explosion – Hiroshima, Japan.

References:

• Collins, G.S., Artemieva, N., Wünnemann, K., Bland, P.A., Reimold, W.U., and C. Koeberl (2008). “Comment article: Evidence that Lake Cheko is not an impact crater.” Terra Nova 20: 165-168.

June 30, 1817 (a Monday)

Joseph Hooker (seated, far left) and on the ground next to him, Asa Gray – 2 of the first 3 men to whom Darwin revealed his theory of evolution by natural selection (July, 1877 U.S. Geological Survey at La Veta Pass, CO)

On this date, the physician, botanist, and biogeographer Joseph Dalton Hooker was born in Halesworth in the county of Suffolk, England. He trained as a doctor in Edinburgh, but his principal interest was in botany.

Joseph Hooker (1896)

Hooker was a close friend and supporter of Charles Darwin. When he realized that Alfred Russel Wallace was about to present his findings on evolution to the public which were similar to Darwin’s, he helped arrange for the shared presentation of Darwin ‘s and Wallace’s papers to the Linnaean Society of London in 1858.

Hooker came to America in 1877 to explore the flora of the Rocky Mountains of Colorado and the Sierra Nevada Mountains of California. He traveled to Pueblo, Colorado with a group of colleagues including Asa Gray. Later, Hooker traveled to La Veta Pass, CO and camped with a group of naturalists and explorers. The group later traveled to the Sangre de Cristo range where Hooker and Gray conducted a plant survey and wrote a manuscript about their experience, The Vegetation of the Rocky Mountain Region and a comparison with that of other parts of the World (1880).

June 30, 1860 (a Saturday)

A cartoon from Vanity Fair depicting Bishop Samuel Wilberforce.

On this date, one of the most memorable dramas in the history of science took place at the annual meeting of the British Association for the Advancement of Science at Oxford University. Darwin’s The Origin of Species had been published in 1859, but his health was not good enough to allow him to go to the Oxford meeting. However, Thomas Henry Huxley was there and it was he who so brilliantly debated Darwinism with Bishop Samuel Wilberforce of the Church of England. More than 700 people crowded into the lecture room on that day – so many, in fact, that the meeting had to be moved to the library of the University Museum. Wilberforce, having refused to regard monkeys as his ancestors, turned to Huxley during the debate and asked whether it was through his grandfather or his grandmother that he claimed descent from “a venerable ape.” Huxley took the challenge and is reputed to have answered, “If I am asked whether I would choose to be descended from the poor animal of low intelligence and stooping gait, who grins and chatters as we pass, or from a man, endowed with great ability and splendid position, who should use these gifts to discredit and crush humble seekers after truth, I hesitate what answer to make!”