Newsletter No. 202
The Black Country Geological Society
The academic papers concerning the topic are:
Proposing snowball Earth: Paul F. Hoffman and Daniel P. Schrag: The snowball Earth hypothesis: testing the limits of global change. (In Terra Nova, 14, 129-155, 2002)
Questioning snowball Earth: Nick Eyles: Glacio-epochs and the supercontinent cycle after ~3.0 Ga: Tectonic boundary conditions for glaciation. (In Palaeogeography, Palaeoclimatology, Palaeoecology 258 (2008) 89-129)
For a very good overview:
Ian J. Fairchild and Martin J Kennedy: Neoproterozoic glaciation in the Earth System. (In Journal of the Geological Society, London, Vol. 164, 2007, pp. 895-921.)
Ian Fairchild’s research on this topic can be seen on the University of Birmingham web site; Schools and Departments → Geography, Earth and Environmental Sciences → Staff.
Further Fine Fossil Facts From Forests
Following my article in Newsletter 200 for April 2010, I have discovered a few more interesting features concerning the three trees which were first known from their fossils.
Fossilised parts of this tree have been found in coal seams dating from 250mya. There were quite a few other members of the ginkgo family, but ginkgo biloba is the sole survivor. It is unique in the way it reproduces. Fertilisation is effected by free swimming male sperm which reach the ovules through a film of water. This is the reproductive habit of modern ferns, but it occurs in no other known tree. This raises some interesting questions, as male and female flowers grow on separate trees, so how does the sperm reach the female flower? I need to do some more research into this interesting problem.
The tree survived for centuries by cultivation in temple gardens in China. Its generic name ginkgo is said to be derived from the Chinese “xinkuo”, meaning the “silver fruit” that the tree sometimes bears. Incidentally, on a recent visit to Dartmouth I noticed a fine specimen in the park in the centre of the town. There is also another in the grounds of Haden Hill House, Beauty Bank, Old Hill, as well as my small sapling.
Metasequoia Glyptostroboides, or Dawn Redwood
Until 1941, the dawn redwood was known to scientists only from fossil remains, and was believed to have been extinct since the Pliocene era, which ended about 2 mya. Chinese botanists discovered many specimens in Hupei and Szechwan Provinces. In 1948 seeds were collected from a natural and planted stand of about 1000 trees in the Shui-Sha valley in Hupei Province and sent to botanical gardens and arboreta all over the world. It can be reproduced easily from cuttings, so it is widely distributed in Britain except for Scotland where summers are too cold. The bark is pale orange-brown peeling off in brown plates or fibres. The trees come into leaf in early May. The leaves are straight or sickle shaped, about 10-35mm long, bluish green above, ashy green beneath and they turn red in autumn before leaf fall.
Incidentally, its near relative, the Swamp cypress (Taxodium distichum) grew in Britain 2mya ago, as traces of it have been found in rocks near Bournemouth. ►