EARLY LIFEThe story of life on Earth began more than 3500 million years ago in the Archean Eon, when the first primitive living things (tiny single celled organisms) evolved in the ancient seas that covered the Earth. In the Archean seas, the earliest forms of life know as Archaea were thriving in environments that were hostile and considered inhospitable. They survived in the hot, poisonous and almost oxygen free environment by using other chemicals for their energy.
For nearly 2000 million years, all living things were single celled. Algae emerged as the first multi-cellular living things. Tiny bacterial cells called Cyanobacteria evolved soon after algae. They could produce their own food, just like plants do today, releasing oxygen in the process. About 180 millions of years later, larger more complex single cells evolved. These types of cells known as Eukaryote cells, are the same as those that make up the bodies of modern flora and fauna. Late in the Proterozoic Eon, multicellular soft-bodied animals evolved in the seas. The continents were not in the same positions as they are today. Although there was some land above sea level, at this time all life was found in the seas. The seas were abundant with life. The Palaeozic Era began with a burst of evolution resulting in huge diversity of sea-dwelling animals. During the last 500 million years, the continents shifted around the globe. Geological forces were the cause for this change, merging the continents together and splitting them apart. Climates fluctuated from warm to cool. Due to this extreme change, by the end of the Palaeozic Era, more than 90 per cent of all plant and animal species were wiped out in a mass extinction. This marked the end for 90 per cent of plant and animal history during this time. The surviving ancestors of all major plant and animal groups evolved. This resulted in the first plant and animal species living on the land. MOVING ONTO LANDEvidence of the transition to life on land comes from the Ordovician age 490-434 millions of years ago, when arthropods such as sea scorpions moved from marine to freshwater environments. The tracks made by these animals walking on land have survived as fossils. True land-dwelling arthropods and plants appear in the fossil records at the end of the Silurlan period about 410 millions years ago. Amphibians were the first vertebrate animals to walk on land in the late Devonian age, about 370 millions years ago. Early amphibians evolved in water and had skulls, backbones and limb structures.
During the Carboniferous period, 354-298 millions of years, the giant Clubmoss trees that evolved earlier in the Devonian period continue to dominate the swamps. Towards the end of this period an ice age developed. This continued into the beginning of the Permian age between 298-270 millions of years ago. After this ice age the vegetation changed to low-growing ferns and horsetails. SWIMMING REPTILES AND FISHWhile dinosaurs ruled the land, some animals took to and dominated the waters. Diversity was no different in the vast waters and freshwater systems than what it was on land, there were other animals with backbones, the fish.
An early group of swimming reptiles, the Nothosaurs, evolved and became extinct during the Triassic. They had webbed feet rather than the paddles of later swimming reptiles and may have spent some time on land. Ichthyosaurus had well-developed paddles for swimming, evolving in the Triassic and dying out by the middle of the Cretaceous period. A completely different group of swimming lizards the Mososaurs, took to the seas in the late Cretaceous period and evolved rapidly into 70 different species. All had large curved and serrated teeth, however like many other reptiles they became extinct at the end of the Cretaceous period. Both sharks and bony fish suffered massive losses of species during the mass extinction at the end of the Permian period. Species diversity started to increase again during the Triassic and Jurassic. However it was in the Cretaceous period that the ancestors of many modern groups of fish first evolved. MESOZOIC INSECTSInsects had been around for many millions of years before the Mesozoic period had even begun. However, it was during this era that the more modern groups had evolved.
In the late Jurassic, around 150 millions of years ago, a large warm lagoon covered the area that is now Bavana in Germany. Around this lagoon grew a diverse range of plants and trees that provided an environment with perfect conditions for these insects to thrive and survive. The abundance of insects created a perfect source of food for the flying bird-like reptiles to prey on. The land that we know as China today emerged from the sea during the late Jurassic and early Crustaceous periods. It too was surrounded by rich vegetation. It was the home to a wide variety of insects and spiders, which were also preyed on by early types of birds. RECENT LIFEThe mass extinction at the end of the Cretaceous period 65 million years ago, marked the end of the Mesozoic Era and beginning of the time of 'recent' life, the Cainozoic Era. This Era is divided into the Tertiary and Quaternary Periods
In the first part of the Tertiary, those animals and plant groups that survived the mass extinction were evolving into new forms. Climates fluctuated in the Tertiary between warm and wet and cool and dry conditions. The early Quaternary is better know as the ice age. Throughout the Era the continents continued to move closer to their current positions today. As a result, plant and animal species were evolving differently in the northern and southern hemispheres. However, collisions in the land masses caused land bridges which allowed migrations of species to take place. Homo sapiens (humans) evolved in the last half of millions of years. Scientists argue that the rapid rise and spread of our species and the major impact our lifestyles have on the environment, could cause the next mass extinction. |
RULING REPTILESAlthough Dinosaurs evolved in the Triassic, they were not particularly abundant at this stage. Crocodile-like, Lizard-like, mammal-like and flying reptiles ruled the land and sky during this time.
During the Jurassic period dinosaurs flourished, with a diverse range of dinosaur species roaming the earth. Long-necked Sauropods, armoured herbivores and large carnivores evolved throughout this time. Tyrannosaurus Rex was one of these large carnivores, growing more than 12 meters long with dagger like teeth, while the gigantic herbivore Brachiosaurus gently roamed the Earth feeding on plants. By the Cretaceous period, the super continent Pangea had broken up and different species of dinosaurs evolved on different continents. AQUATIC INVERTEBRATESThe Permian mass extinction hit invertebrate groups the hardest. At the beginning of the Mesozoic, the underwater gardens of coral and other animals attached to the sea floor were in ruins. However, some species managed to survive, building up the reefs again creating newly evolved forms of mobile animals.
Brittlestars, Crinoids and sea urchins, relatives of the modern starfish, emerged from these ruins. Brittlestars and sea urchins crawled over the surface of the reef while most Crinoids lived attached to stalks on the sea bed capturing food from the water with their arms. Shelled animals such as Branipods and bivalve molluscs including oysters, filtered their food out of the water. Snail like gastropod molluscs moved around scraping up tiny pieces of food, while later species became predatory. Belemnites and ammonites swam above reefs preying on fish and other animals. Evolving in the Jurassic, the prawn-lobster crab and a similar group of arthropods went onto to become one of the most diverse groups in the Crustaceous period and beyond. Prawns were swimming filter feeders, while lobsters and crabs were bottom-dwelling hunters or scavengers, PLANT LIFEPlant life throughout the Mesozoic period changed from ancient to modern plants. Many ancient plant groups survived the Permian mass extinction but declined throughout the Mesozoic age. During the Crustaceous period, modern plant groups evolved and began their domination of the Earth.
Primitive seed producing plants such as ferns, were still abundant in the Triassic period, however it was conifers with their seeds enclosed in cones that dominated the forests of the Mesozoic age. By the time the Crustaceous period came around, flowering plants and plants bearing fruit began to evolve into the modern groups, such as grasses, herbs, roses and gum, fruit and oaks trees that we know today. LEARNING FROM THE PASTFossil records give us an understanding of how animals and plants and the environments they lived in, have changed overtime.
Throughout the Earth's history there have been periods of mass extinction, when large numbers of plant and animal species die out. They usually occur over thousands or millions of years. Today, extinction rates are much faster. In the next hundred years, thousands of todays species could become extinct. In Australia alone, 3000 plant and over 400 vertebrate and an undisclosed number of invertebrate species will be threatened by extinction. In order to reduce the threats of extinction we need to lessen the impact of human lifestyle on the Earth and its other inhabitants- reducing population growth, consuming less and therefore reducing pollution. Every individual can make a difference, even you! |