Welcome to the Lickeys Ridge Voyage in DeepTime. The first Voyage site is at the Visitor Centre, which provides you with some basic information – helpful but not essential to the Voyage – so if you are short of time go straight to site 2 the View Point. Otherwise move to the next screen for this site.
At this site you will learn about the geological time scale, plate tectonics and the rock cycle.
Lickey Hills Ridge
What makes the long ridge of the Lickey Hills – why are the hills here? This Voyage provides answers by examining the evidence for volcanic activity, a lost ocean, rainforests, deserts and flash floods that have led to the Lickey Hills of today. This first Task gives you the background to understand these things as they are explored at other task sites. It explains some basic concepts about how the Earth works. Carefully look through the Task 1 information screens and then answer the Task 1 questions (by pressing ‘do it’). So carefully look through the Task 1 material then carry out the Task 1 questions. If you are just out for a short walk today and do not have time to read the information for Task Site 1 (Visitor Centre), that is OK – it helps, but it is not essential. You can start your Voyage at Task Site 2 if you prefer. Strange noises? – touch the ‘+’ button for an explanation (see next paragraph).
Strange noises are a bit of fun at suggesting how this place may have sounded in the deep time past. The Visitor Centre sits over rocks from a time when some of the earliest dinosaurs were about. Up in the car park you are over rocks that formed when this area was near the shore of long vanished warm ocean. You can always switch these background sounds off in the options to be found by swiping down to the bottom of the HELP section.
Periods of deep time
The Earth has not always looked as it does today. Scientists have worked out that the Earth is over 4500 million years old. They know this from studying the rocks of the Earth, or its geology, which give us evidence of how the surface of our planet has changed over time. To make it easier to comprehend and to study so many millions of years, we divide the age of the Earth into blocks of time, known as geological Periods, which are give the names shown in the column on the left side of the picture (move the image about to see all the names and information about life): Also touch the clock (in the app) to get a timescale for all 4500 millions years of the planet’s existence.
Some people recall the order of the Periods by remembering the following sentence:
Pink Camels Often Sit Down Carefully; Perhaps They Just Can’t Think Quickly
Rocks of Britain
In the British Isles we have rocks from every single geological Period, including some of the oldest Precambrian rocks in the world in NW Scotland (over 3000 million years old) to some of the youngest rocks in SE England. As you complete your Deep Time Voyage around the Lickey Hills, you will travel through four of these ancient periods of time and find out what the landscape here looked like then.
Britain is a place where it is possible to see rocks from a significant amount of the planet’s history, without having to travel far, or find yourself travelling great distances over rock of essentially the same age and type. This variety is due to the fact that the pieces of the Earth’s crust that form Britain today, have had a long turbulent journey through deep time.
The surface of the Earth is formed from enormous, rigid slabs of rock known as tectonic plates, which can be from about 15 km to over 200 km thick. The plates ‘float’ on more fluid rock below, so they are constantly moving, but very slowly, at about 2 – 5 cm a year, about the speed at which your fingernails grow. This means that the continents on the plates move slowly too, but over millions of years they can travel a very long way.
The Eurasia plate you are on now is moving NE at about 2cm per year. Over an average human life span of some 85 years, the Lickey Hills will have moved around 1.7 metres NE. We can track the relative movement of plates using the precision provided by GPS. The change in the location of places requires the periodic updating of navigation based systems. For example the current position of Australia is about 1.5 metres further north than existing maps suggest it to be – the Australian plate moves north at about 7cm per year. Such growing errors will pose a treat to autonomous cars and other systems that rely on very precise GPS positioning.
As the tectonic plates move they interact along their edges. We feel the movements as earthquakes. Sometimes they slide past one another, at some places they pull apart and at others, they collide. Where there are oceans on the plates, the rock beneath the sea bed is very dense. This means that when plates collide, the less dense plate will ride over the other, and the denser plate will sink down into the depths of the Earth. This is what is happening today at places such as the west coast of South America where a dense oceanic plate is sinking under the South American continent at what is called a ‘subduction zone’.
In a subduction zone, as the oceanic plate sinks, it carries water down the trench with it. The water reduces the melting temperature of rock, so at depth, rock melts above the subduction zone. The molten rock is even less dense than the continent above, so the molten rock, or magma, rises, pushing up through the crust, and forms volcanoes – as can been seen all down the west coast of South America.
Plates colliding and pulling apart
When two continental plates collide, the rocks of the continental crust will buckle as the two plates collide and a great mountain range will rise. The Himalayan mountain range is forming in this way as the Indian plate is pushing northwards against the Eurasian plate. In other locations on Earth, the tectonic plates are pulling apart, and this allows magma to rise from beneath the plates, filling the gap and forming new crust. The molten rock will flow out at the surface and is then called lava.
All the way down the Atlantic Ocean there is a plate boundary between two oceanic plates, known as the Mid-Atlantic Ridge. New crust is being formed as lava flows out at the surface on the ocean floor.\n\nIceland is land that has formed where the plates are pulling apart and magma is erupting. It is right above the Mid-Atlantic ridge, but at a part where there is also a ‘hot spot’, where extra heat from the Earth’s interior is providing the energy to erupt vast amounts of magma – enough to reach the surface of the ocean and form islands. In 1963 a volcano that had been erupting from the sea floor, rose dramatically above the water to form a completely new island called Surtsey, off the southwest coast of Iceland. Picture below – Surtsey forming.
From magma to igneous rock
When magma rises from the hot depths of the Earth towards the surface, it cools and becomes solid rock made up of interlocking mineral crystals. This is called igneous rock. The other two main rock types are sedimentary and metamorphic. We will learn about those later.
The faster the magma cools, the smaller the crystals will be in the new igneous rock. If it makes it to the surface, magma will cool quickly and a rock such as basalt will form. On the other hand, granite is a rock that formed as magma cooled slowly below the land surface. It has big crystals that are easy to see.
From mountains to sedimentary rock
Mountains and volcanoes are some of the highest places on the Earth and once they have formed, they quickly start to erode as they are battered by wind and rain, or frozen by ice, or heated by the sun. Boulders and fragments of rock roll down mountain slopes or are carried by water or ice. As they travel they knock against one another and become smaller cobbles and pebbles and may even break down into grains of sand or mud, becoming smaller the further they travel. Eventually this ‘sediment’ will come to rest, usually in the bed of a river or lake or in the sea, or in the dunes of a desert. Layers of sediment build up one on top of another and the lower layers are compressed back into rock by the weight of the layers above them. The sediment may also be cemented together by dissolved minerals as water seeps through it. This is how most sedimentary rocks form.
There is one other way that a special kind of sedimentary rock forms in the sea. Limestone is a sedimentary rock made up of the broken or dissolved remains of shelly sea creatures that have died and fallen to the sea floor. Layers build up and are cemented together by the mineral calcite, which is what the shells of sea creatures are made of.
Heat+pressure make metamorphic rock!
Metamorphic rocks form when other types of rock (igneous or sedimentary) are altered by intense heat and/or pressure as they are squeezed or buried deep in the Earth by the movement of tectonic plates, or heated because of the presence of very hot magma. The minerals in the original rock are changed chemically and the physical structure and appearance of the rock may alter. Metamorphic rocks often have interesting swirling textures or a beautiful lustrous appearance – see the schist in the photo below.
The names of some metamorphic rocks may be quite familiar to you, such as slate (which is altered mudstone) and marble (which was originally limestone). The metamorphic rocks in the pictures are probably less well known – the swirly one is called gneiss and the lustrous one is a schist.
The present is the key to the past
Most of the rocks that we find on the Earth have taken millions of years to form, but the processes that formed them are still making new igneous, sedimentary and metamorphic rocks all over the world today. Sometimes, in old rocks, we find fossils – the remains of plants or animals that lived long ago, turned to stone. As geological detectives we can look at how rocks are forming and how animals live today and apply this understanding to what has happened in the past. For example, we know that red sandstones are forming in modern deserts (see photo below) and that corals only live in warm, clear, shallow seas. If we find rocks made of red sandstone or containing fossilised coral then it gives us an idea of what the environment in the area was like at the time the rocks formed, millions of years ago.
The phrase ‘the present is the key to the past’ is a simple but very powerful concept in geology – it is even given a name – it is called Uniformitarianism. It means that processes that are occurring today have operated throughout most of the Earth’s history. Limestones and sandstones form in exactly the same way today as they did in the past. This idea was first proposed by pioneering geologists, James Hutton and Charles Lyell in Scotland in the 18th and 19th centuries. Indeed the science of geology originated in Britain. The huge variety of rocks from all the different periods of geological time that we have in the British Isles served as a natural laboratory, allowing the early geologists to observe and map the different rocks and comprehend the scale of geological time and the means by which it could be correlated.
Route to Task Site 2
Answer the Visitor Centre task questions by touching ‘do it’ then leave the Visitor Centre in the direction shown here – walk up into the car park and continue on into the upper car park.
Route to Task Site 2
Leave the upper car park in the direction heading towards a broad level path where you will find the Landscape and Rocks information panel – site of Task 2. If you have ‘audio alerts Task site’ switched on, you will here ‘Entered Task Site’ as you approach sites. This feature is switched off by default, to activate it swipe down to the bottom of Help where you will find the switch.
Task Site 2 Questions
Find the direction this area has moved through geological time. In the app touch the clock for information and scroll/slide the time scale.
a) Moved northwards from S Pole over last 700 million years
b) Moved southwards from N Pole over last 300 million years
c) Moved westwards from the USA over the last 500 million years
d) Not changed position at all over last 1000 million years
What do you think will usually happen when two continental plates collide.
a) Neither is very dense so they will change direction and slide past each other
b) The thicker plate must be heavier so that one will sink
he rock of the plates will buckle, thicken and form a mountain range
Rock that has formed from cooled magma is one of the three main rock types. Known as:
a) Sedimentary rock
b) Igneous rock
c) Metamorphic rock
Which of the following is a sedimentary rock:
Which of the following do you think is a metamorphic rock:
a, b, c or d