B3-Life on Earth

A summary of the 21st century Science Module B3-Life on Earth

HideShow resource information

The Variety Of Life

  • Scientists use similarities and differences between living things to classify them
  • A species is a group of organisms that can breed together and produce fertile children
  • Variation is important in evolution. It can be cause by genes (genetic variation), your environment (environmental variation) or both
  • Almost all variation is caused by both genes and environment
  • Life on Earth started from simple living things. These changed (evolved) to produce all the things on the Earth today. These changes also made some species extinct
  • Fossils are made from the bodies of living things. Almost all fossils are from extinct creatures, 99% of all species that have ever been on Earth are extinct
  • Conditions have to be perfect to form fossils, so very few species end up as fossils
  • Although there are gaps in the fossil records, scientists have collected 1,000,000's of fossils
  • Evolution never happens at the same speed, it happens in spurts over 1000's of years
  • Scientists can compare the genes of living things to see if they are related
1 of 7

Evidence for change

  • Species are evolving now and are mainly caused by humans
  • Early farmers noticed variation between crops and animals and used the most successful ones for breeding (selective breeding)
  • 1 shampoo was used to kill head lice, but soon 1 louse became resistant and survived to breed. It's children also became resistant and a new shampoo was used.
  • Most changes to species happened before humans arrived, something in the environment caused them to change (natural selection). Natural selection is how evolution happens
  • Individuals in a species have variation and they compete ( for food, shelter and a mate). Some individuals will have a feature that makes them more successful and they breed. Their genes are passed to their offspring and more of the next generation has the useful feature
2 of 7

The Story of Charles Darwin

  • Charles Darwin noticed that some animals in a population are better suited to survive than others. They would breed and pass on their features to the next.This natural selection would make a species change over time. Darwin explained evolution and proved it by using fossils
  • A good explanation accounts for all observations and explains a new link
  • There were 3 problems with Darwin's theory. The fossil record was incomplete, the age of the Earth was unknown, so there didn't seem to be enough time for natural selection. These 2 problems have now been solved
  • Lastly, Darwin could not explain why species are varied and how features are inherited. These have been answered with genes
  • Mendel discovered dominant and recessive alleles and how information is inherited
  • When DNA is copied (to make new cells) mistakes can occur and cause mutations
  • Mutations produce differences in a species, they are a cause of variation
  • Most mutations have no effect on the individual. Rarely, they cause a change that improves survival and if the mutation is in a sex cell, it will be passed to the offspring
3 of 7

Where Did Life Come From?

  • Life on earth began about 3500 Million years ago.
  • Living things can all reproduce, the first living thing were molecules that could copy themselves.
  • Scientists have 2 ideas about where life came from: 1 - life started somewhere in the solar system and was brought to earth on a comet; 2 - life started at the bottom of the ocean in bubbles of iron sulfide.
  • Conditions on earth 3500 mil. yrs ago were different to now but the living things were suited to the conditions.
  • Iona marble contains the oldest living things in Britain formed from the remains of billions of single cell organisms.
  • The 1st living things were only one cell, multi-cellular organisms appeared millions of years later.
  • Multi cellular things could get bigger and cells could become specialised. The cells changed so that they could do one job better.
  • Bigger multi cellular organisms needed ways for cells to communicate.
4 of 7

Keep in Touch

  • Many changes happen inside the body and the organisms communication systems must respond, in order to survive
  • Homeostasis is keeping a steady state inside the body
  • Your body communicates in 2 different ways. 1- Neurons (nerve cells) carry electrical impulses to parts of the body. 2- Hormones are chemicals that are carried in the blood.They are made in one body part and affect another
  • Neurons carry electrical impulses fast but they only last a short time.
  • Receptors detect a stimulus and send a nerve impulse to the brain and spinal cord (central nervous system). The CNS processes the info. and sends an impulse to an effector (muscle) which causes a response.
  • Hormones are used when you need a response that is slow and long-lasting, like growing.
  • Hormones are made by parts of the body called glands - thyroid, pituitary, pancreas, adrenal, ovaries and testis
5 of 7

Human Evolution

  • Apes and humans share many features. They evolved from an ancestor and at some point developed differently.
  • Humans have 2 differences from apes, 1 - bigger brains, 2 - walk upright. Scientists predicted that big brains came before walking upright.
  • The skull of a hominid was found in Africa. Hominids are more like humans than apes and lived 1.4 Mil Yrs ago. They had small brains but walked upright.
  • In Africa 7 Mil Yrs ago grass was tall and hominid had to stand up to see over it. This helped them survive.
  • There were several species of hominid which shared a common ancestor. Most of these species died out apart from the ones that had bigger brains. This species evolved into modern humans.
6 of 7


  • Most species that have lived on e4arth in the last few million yrs have become extinct.
  • There is fossil evidence of at least 5 mass extinctions on earth and we are beginning one.
  • Changes in a habitat can put animals at risk of extinction. They are endangered.
  • Changes in factors like food and temperature can make things endangered.
  • New species can put animals at risk in 3 ways, 1 - species compete with each other for food, 2 - the new species could be a predator, 3 - new species could cause a disease.
  • Animals in a food web are joined together and a new animal could effect the whole food web.
  • Human beings can cause other species to become extinct in 2 ways, 1 - directly (by hunting), 2 - in-directly (taking away the habitat).
  • Biodiversity is the variety of life on earth.
  • Sustainability means meeting the means of people today without damaging for the people of the future.
7 of 7


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Evolution, extinction and natural selection resources »