Nature 2021 April

The best of both worlds

Two events over the last few weeks have reawakened the question: are we alone in the universe or has life also developed somewhere other than planet Earth?

The first event, in February 2021, was the successful landing of NASA’s Mars Explorer, called the Perseverance Rover. It landed in a near-equatorial crater called Jezero, to search for evidence of life that once existed on Mars.

Over the next Martian year, which is two Earth years, Perseverance will journey around 9.5 miles or 15 km. The mission involves visiting several different rock formations in the crater and surrounding area. The purpose is to see whether this might reveal if there is any evidence in the silt and sediment of biological activity. The location was chosen from careful interpretation of satellite imagery which identified it to be a river delta – a topographic feature built up from the silt and sand dumped by a river as it enters a wider body of water. This wider body is believed to have been a lake which existed billions of years ago.

Unless there is conclusive evidence from biochemical signatures of life, the on-site analysis of sediment samples will have to wait until at least 2026, when the proposed Mars Sample Return Mission is planned to take place. A further update will have to await one of my 2026 Hilltop News!

The second event, the ‘Winchcombe Fireball’, as some of the tabloids tagged it, was seen all across northern Europe and was heard (a sonic boom) in the skies above Gloucestershire on the night of 28 February 2021.

One fragment, weighing 11 oz (300g), was found on the driveway of a house in Winchcombe. More fragments were found in a nearby field. The meteorite was of carbonaceous chondrite, which signals it is of ancient heritage: a rocky material left over from the formation of the Solar System some 4.6 billion years ago. This is the first example found in the UK and it contains the basic organic materials and extra-terrestrial amino acids which are the ingredients required to provide the basics for organism creation on a planet like Earth. The perfect porridge for Goldilocks, just 3.77 billion years late! In comparison to Mars, Earth is definitely… ‘the Best of Both Worlds’. From this ideal porridge, life first appeared on Earth and has evolved as we know it today. However, Goldilocks does not remain unchanged.

How much of the land surface visible today is truly natural? Very little! Take Iceland. It appears to be largely a wilderness, a truly original landscape. Far from it – the island was once covered by spruce forest. Much of this has now disappeared or has been altered by intensive sheep farming. The countryside of southern England, with its characteristic patchwork of hedged fields and woodlands, is totally manmade, having replaced the oak forests that emerged as the dominant habitat after the last Ice Age.

There is an irony here. True cities and towns at one level represent the most dramatic contrast to the rural landscape. It might easily be assumed that with natural habitats stripped away and blanketed by buildings, roads, and industrial expanses of concrete and metal they are the very antithesis of the English countryside.

Though all towns and cities are not the same, civic planning in the UK has provided a rough template of inner city, suburbs and protective margin or green Belt. Despite its immense size London is by any measure a ‘green’ city. It has many parks, squares and commons: its ‘lungs’ and a large part of it has even has been designated the London City National Park.

Inside the 14,000 hectares (35,000 acres) of Edinburgh there are over a million trees. 84% of these trees are in gardens and the remainder in parks or along roads. This works out at 56 trees per hectare. What is remarkable about this is that in the rural area surrounding Edinburgh there are only 43 trees per hectare.

Three-quarters of all animals found in the UK are insects. Hardwood trees like oak provide a rich habitat for insects and therefore these trees are also a most productive niche providing abundant food for predators and numerous hosts for parasites. Though many individual species of birds, mammals, insects, wild-flowers or trees, fungi, mosses and liverworts can only be found outside our towns and cities, the variety of species and the populations to be found in our urban areas is also very large. Just take birds. Most are predators of insects but many are also fruit and seed eaters, essential if they are to survive harsh winters when insects are very scarce.

A typical English suburban garden will include several shrubs with colourful fruits. Take just one example, holly. Native holly varieties can be found in large numbers growing wild and out of control in our woodlands. But holly is equally in abundance in both its indigenous form and numerous cultivar varieties in urban centre parks and suburban gardens. Female bushes are favoured in gardens as they bear fruits. From the early Spring, leaf miner insects invade the soft centres between the tough top and bottom leaf cuticles, which provide them with a level of protection and nutritious food. Blue tits can extract these miners like an expert winkle picker.

Largely inconspicuous flowers appear in late Spring and Summer and are pollinated mainly by equally inconspicuous flies attracted by strong nectar. Small spiders lie in waiting for one of these small flies to get caught in web traps. In the autumn blackbirds and song thrushes can strip a holly tree, though in good years there may be some left for visiting redwings and fieldfares. Holly holds its leaves well but when they fall there are worms, fungi and soil bacteria near the soil surface that can quickly digest them and generate rich humus. Before they disappear, the leaf litter provides a possible refuge for woodlice, centipedes and beetles. However, a hedgehog or shrew will easily root them out. All-in-all, holly and the many other fruit-bearing bushes will support its own unique interconnected web of wildlife.

In a rural landscape, the flora and fauna at large in the fields, woods or the commons around us decide where they choose to wander. Unlike the otherwise similar gardens to be found in town cities and suburbs, whether we like it or not, our gardens are greatly enriched by the wildlife that inhabits the countryside around us. You could say, in contrast to those living in towns or cities or suburbs, we have picked the Goldilocks porridge and you could say I suppose … the best of both worlds.

Chris Brown
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