Ice Adhesion
Description
The strategies currently used to combat ice accumulation problems involve chemical, mechanical or electrical approaches. These are expensive and labor intensive, and the use of chemicals raises serious environmental concerns. The availability of truly icephobic surfaces or coatings will be a big boon in preventing the devastating effects of ice accumulation. Currently, there is tremendous interest in harnessing nanotechnology in rendering surfaces icephobic or in devising icephobic surface materials and coatings, and all signals indicate that such interest will continue unabated in the future. As the key issue regarding icephobic materials or coatings is their durability, much effort is being spent in developing surface materials or coatings which can be effective over a long period. With the tremendous activity in this arena, there is strong hope that in the not too distant future, durable surface materials or coatings will come to fruition.
This book contains 20 chapters by subject matter experts and is divided into three parts-- Part 1: Fundamentals of Ice Formation and Characterization; Part 2: Ice Adhesion and Its Measurement; and Part 3: Methods to Mitigate Ice Adhesion. The topics covered include: factors influencing the formation, adhesion and friction of ice; ice nucleation on solid surfaces; physics of ice nucleation and growth on a surface; condensation frosting; defrosting properties of structured surfaces; relationship between surface free energy and ice adhesion to surfaces; metrology of ice adhesion; test methods for quantifying ice adhesion strength to surfaces; interlaboratory studies of ice adhesion strength; mechanisms of surface icing and deicing technologies; icephobicities of superhydrophobic surfaces; anti-icing using microstructured surfaces; icephobic surfaces: features and challenges; bio-inspired anti-icing surface materials; durability of anti-icing coatings; durability of icephobic coatings; bio-inspired icephobic coatings; protection from ice accretion on aircraft; and numerical modeling and its application to inflight icing.
More details
Other editions
Additional editions
Persons
Kashmiri Lal Mittal was employed by the IBM Corporation from 1972 through 1993. Currently, he is teaching and consulting worldwide in the broad areas of adhesion as well as surface cleaning. He has received numerous awards and honors including the title of doctor honoris causa from Maria Curie- Sklodowska University, Lublin, Poland. He is the editor of more than 135 books dealing with adhesion measurement, adhesion of polymeric coatings, polymer surfaces, adhesive joints, adhesion promoters, thin films, polyimides, surface modification surface cleaning, and surfactants. Dr. Mittal is also the Founding Editor of the journal Reviews of Adhesion and Adhesives.
Chang-Hwan Choi is a professor in the Department of Mechanical Engineering at the Stevens Institute of Technology. He acquired his BS (1995) and MS (1997) in Mechanical & Aerospace Engineering from Seoul National University in Korea. He worked as a researcher at Korea Aerospace Research Institute before he received his PhD (2006) in Mechanical Engineering from the University of California at Los Angeles (UCLA), specializing in MEMS/Nanotechnology and minoring in Fluid Mechanics and Biomedical Engineering. Areas of his research interest include surface engineering and interfacial phenomena. He has published more than 100 peer-reviewed journal articles and been awarded one patent.
Content
Preface xv
Part 1: Fundamentals of Ice Formation and Characterization 1
1 Factors Influencing the Formation, Adhesion, and Friction of Ice 3
Michael J. Wood and Anne-Marie Kietzig
1.1 A Brief History of Man and Ice 4
1.1.1 Ice on Earth 4
1.1.2 Man is Carved of Ice 5
1.1.3 Modern Man Carves Ice 8
1.2 A Thermodynamically Designed Anti-Icing Surface 13
1.2.1 Homogeneous Classical Nucleation Theory 14
1.2.2 Heterogeneous Classical Nucleation Theory 16
1.2.3 Predicting Delays in Ice Nucleation 20
1.2.4 Predicting Ice Nucleation Temperatures 22
1.3 The Adhesion of Ice to Surfaces 25
1.3.1 Wetting and Icing of Ideal Surfaces 26
1.3.2 Wetting of Real Surfaces 30
1.3.3 Ice Adhesion to Real Surfaces 32
1.4 The Sliding Friction of Ice 38
1.4.1 Ice Friction Regimes 39
1.4.2 The Origin of Ice's Liquid-Like Layer 42
1.4.3 Parameters Affecting The Friction Coefficient of Ice 43
1. 5 Summary 45
References 46
2 Water and Ice Nucleation on Solid Surfaces 55
Youmin Hou, Hans-Jürgen Butt and Michael Kappl
2.1 Introduction 55
2.2 Classical Nucleation Theory 57
2.2.1 Homogeneous Nucleation Rate 59
2.2.1.1 Homogeneous Nucleation of Water Droplets and Ice from Vapor 60
2.2.1.2 Homogeneous Ice Nucleation in Supercooled Water 61
2.2.2 Heterogeneous Nucleation Rate 63
2.2.2.1 Heterogeneous Water Nucleation on Solid Surfaces 63
2.2.3 Spatial Control of Water Nucleation on Nanoengineered Surfaces 68
2.2.4 Heterogeneous Ice Nucleation in Supercooled Water 71
2.3 Prospects 76
2.4 Summary 78
Acknowledgement 79
References 79
3 Physics of Ice Nucleation and Growth on a Surface 87
Alireza Hakimian, Sina Nazifi and Hadi Ghasemi
3.1 Ice Nucleation 88
3.2 Ice Growth 94
3.2.1 Scenario I: Droplet in an Environment without Airflow 95
3.2.2 Scenario II: Droplet in an Environment with External Airflow 99
3.3 Ice Bridging Phenomenon 105
3.4 Summary 108
References 109
4 Condensation Frosting 111
S. Farzad Ahmadi and Jonathan B. Boreyko
4.1 Introduction 111
4.2 Why Supercooled Condensation? 114
4.3 Inter-Droplet Freeze Fronts 117
4.4 Dry Zones and Anti-Frosting Surfaces 124
4.5 Summary and Future Directions 129
References 131
5 The Role of Droplet Dynamics in Condensation Frosting 135
Amy Rachel Betz
5.1 Introduction 135
5.2 Nucleation 137
5.3 Growth 138
5.4 Coalescence and Sweeping 139
5.5 Regeneration or Re-Nucleation 146
5.6 Inception of Freezing 147
5.7 Freezing Front Propagation 149
5.8 Ice Bridging 150
5.9 Frost Growth and Densification 153
5.10 Concluding Discussion 155
Acknowledgments 156
References 156
6 Defrosting Properties of Structured Surfaces 161
S. Farzad Ahmadi and Jonathan B. Boreyko
6.1 Introduction: Defrosting on Smooth Surfaces 162
6.2 Defrosting Heat Exchangers 167
6.3 Dynamic Defrosting on Micro-Grooved Surfaces 170
6.4 Dynamic Defrosting on Liquid-Impregnated Surfaces 172
6.5 Dynamic Defrosting on Nanostructured Superhydrophobic Surfaces 176
6.6 Summary and Future Directions 179
References 181
Part 2: Ice Adhesion and Its Measurement 187
7 On the Relationship between Surface Free Energy and Ice Adhesion of Flat Anti-Icing Surfaces 189
Salih Ozbay and H. Yildirim Erbil
7.1 Introduction 190
7.2 Types of Ice Formation 193
7.2.1 Ice Formation from Supercooled Drops on a Surface 193
7.2.2 Frost Formation from the Existing Humidity in the Medium 194
7.3 Work of Adhesion, Wettability and Surface Free Energy 195
7.4 Factors Affecting Ice Adhesion Strength and Its Standardization 197
7.5 Effect of Water Contact Angle and Surface Free Energy Parameters on Ice Adhesion Strength 199
7.6 Summary 205
References 206
8 Metrology of Ice Adhesion 217
Alireza Hakimian, Sina Nazifi and Hadi Ghasemi
8.1 Theory of Ice Adhesion to a Surface 218
8.2 Centrifugal Force Method 221
8.3 Peak Force Method 224
8.4 Tensile Force Method 230
8.5 Standard Procedure for Ice Adhesion Measurement 231
8.6 Summary 233
References 233
9 Tensile and Shear Test Methods for Quantifying the Ice Adhesion Strength to a Surface 237
Alexandre Laroche, Maria Jose Grasso, Ali Dolatabadi and Elmar Bonaccurso
Glossary 237
9.1 Introduction 239
9.2 About Ice, Impact Ice, and Ice Adhesion Tests 241
9.2.1 Relationship between Wettability and Ice Adhesion 241
9.2.2 A Simple Picture of Condition-Dependent Ice Growth 246
9.2.3 Factors Affecting Ice Adhesion Strength 248
9.3 Review of Ice Adhesion Test Methods 253
9.3.1 Shear Tests 257
9.3.1.1 Pusher and Lap Shear Tests 257
9.3.1.2 Spinning Test Rigs 263
9.3.1.3 Vibrating Cantilever Tests 269
9.3.2 Tensile Tests 274
9.4 Prospects 279
9.5 Summary 279
Acknowledgements 280
References 280
10 Comparison of Icephobic Materials through Interlaboratory Studies 285
Sigrid Rønneberg, Caroline Laforte, Jianying He and Zhiliang Zhang
10.1 Introduction 286
10.2 Icephobicity and Anti-Icing Surfaces 288
10.3 Ice Formation and Properties 289
10.3.1 Definitions of Ice 290
10.3.2 The Effect of Ice Type on Ice Adhesion Strength 294
10.4 Testing Ice Adhesion 299
10.4.1 Description of Selected Common Ice Adhesion Tests 299
10.4.2 Adhesion Reduction Factor 303
10.4.3 Effect of Experimental Parameters 305
10.4.3.1 Temperature 305
10.4.3.2 Ice Sample Size 307
10.4.3.3 Force Probe Placement and Loading Rate 308
10.5 Comparing Low Ice Adhesion Surfaces with Interlaboratory Tests 310
10.5.1 The Need for Comparability 310
10.5.2 Interlaboratory Test Procedure 311
10.5.3 Interlaboratory Test Results 314
10.5.4 Properties of a Future Standard and Reference 317
10.6 Concluding Remarks 319
References 320
Part 3: Methods to Mitigate Ice Adhesion 325
11 Mechanisms of Surface Icing and Deicing Technologies 327
Ilker S. Bayer
11.1 A Brief Description of Icing and Ice Adhesion 328
11.2 Examples of Mathematical Modeling of Icing on Various Static or Moving Surfaces 331
11.3 New Applications of Common Deicing Compounds 334
11.4 Plasma-Based Deicing Systems 336
11.5 Functional Super (Hydrophilic) or Wettable Polymeric Coatings to Resist Icing 340
11.6 Nanoscale Carbon Coatings with/without Resistive Heating 345
11.7 Antifreeze Proteins 349
11.8 Summary and Perspectives 354
References 355
12 Icephobicities of Superhydrophobic Surfaces 361
Dong Song, Youhua Jiang, Mohammad Amin Sarshar and Chang-Hwan Choi
12.1 Introduction 362
12.2 Anti-Icing Property of Superhydrophobic Surfaces under Dynamic Flow Conditions 369
12.2.1 Preparation of Superhydrophobic Surfaces 369
12.2.2 Anti-Icing Test under Dynamic Flow Conditions 369
12.2.3 Results and Discussion 372
12.3 Analytical Models of Depinning Force on Superhydrophobic Surfaces 374
12.4 Analytical Models of Contact Angles on Superhydrophobic Surfaces 378
12.5 De-Icing Property of Superhydrophobic Surfaces under Static Conditions 381
12.5.1 De-Icing Test under Static Conditions 381
12.5.2 Results and Discussion 382
12.6 Conclusions 384
Acknowledgments 384
References 384
13 Ice Adhesion and Anti-Icing Using Microtextured Surfaces 389
Mool C. Gupta and Alan Mulroney
13.1 Introduction 389
13.1.1 Background 389
13.1.2 State-of-the-Art 392
13.2 Microtextured Surfaces: Wetting Characteristics and Anti-Icing Properties 393
13.2.1 Wetting on Microtextured Surfaces 393
13.2.2 Wetting and Icephobic Surfaces 396
13.2.3 Ice Adhesion to Microtextured Surfaces 398
13.3 Measurement Methods for Ice Adhesion 398
13.3.1 Force Measurement Techniques 399
13.3.2 Contact Area Measurements 400
13.3.3 Measurement Variance and Error 401
13.4 Fabrication Methods for Microtextured Surfaces 402
13.4.1 Micro/Nanoparticle Coatings 402
13.4.2 Chemical Etching 403
13.4.3 Laser Ablation Techniques 404
13.4.4 Embossing Techniques 406
13.5 Microtextured Surfaces and Anti-Icing Applications 407
13.5.1 Solar 408
13.5.2 Wind 409
13.5.3 Aircraft 410
13.5.4 HVAC 410
13.6 Future Outlook 411
Acknowledgments 411
References 412
14 Icephobic Surfaces: Features and Challenges 417
Michael Grizen and Manish K. Tiwari
14.1 Introduction 418
14.2 Features and Challenges in Rational Fabrication of Icephobic Surfaces 418
14.3 Wettability 420
14.4 Surface Engineering 422
14.4.1 Repelling Impacting Droplets 422
14.4.1.1 Drop Impact Characterization 422
14.4.1.2 Enhancing Surface Resistance against Drop Impact 425
14.4.1.3 Additional Factors Affecting Supercooled Droplet Impacts 431
14.4.2 Freezing Delay 432
14.4.2.1 Delaying Freezing of a Droplet 432
14.4.2.2 Delaying Frost Formation 437
14.4.3 Ice Adhesion 443
14.4.3.1 Theory 443
14.4.3.2 Strategies to Lower Ice Adhesion Strength 447
14.5 De-Icing 454
14.5.1 Electro- and Photo-Thermal 455
14.5.2 Magneto- and Photo-Thermal 456
14.6 Summary 457
References 458
15 Bio-Inspired Anti-Icing Surface Materials 467
Shuwang Wu, Yichen Yan, Dong Wu, Zhiyuan He and Ximin He
Glossary of Symbols 468
Glossary of Abbreviations 468
15.1 Introduction 469
15.2 Depressing Ice Nucleation 471
15.3 Retarding Ice Propagation 474
15.4 Reducing Ice Adhesion 479
15.5 All-in-One Anti-Icing Materials 482
15.6 Summary and Conclusions 485
References 486
16 Testing the Durability of Anti-Icing Coatings 495
Sergei A. Kulinich, Denis Masson, Xi-Wen Du and Alexandre M. Emelyanenko
16.1 Introduction 496
16.2 Icing/Deicing Tests and Ice Types 497
16.2.1 Evaluating the Durability of Surfaces 498
16.2.2 Rough Superhydrophobic Surfaces and their Durability 506
16.2.3 Smooth Hydrophobic Surfaces and their Durability 511
16.3 Concluding Remarks 513
References 514
17 Durability Assessment of Icephobic Coatings 521
Alireza Hakimian, Sina Nazifi and Hadi Ghasemi
17.1 Introduction 522
17.2 UV-Induced Degradation 523
17.2.1 Autocatalytic Photo-Induced Degradation Mechanism 523
17.2.2 Factors Affecting UV Resistance 524
17.2.3 UV-Induced Photo-Oxidation Prevention 525
17.3 Hydrolytic Degradation of Coatings 527
17.4 Atmospheric Conditions and Changes in Coating Performance 529
17.5 Mechanical Durability of Coating 532
17.5.1 Cracking 533
17.5.2 Erosion of Coatings 535
17.5.3 Abrasion 536
17.6 Methods for Durability Assessment of an Icephobic Coating 539
17.7 Summary 542
References 543
18 Experimental Investigations on Bio-Inspired Icephobic Coatings for Aircraft Inflight Icing Mitigation 547
Yang Liu and Hui Hu
18.1 Introduction About Aircraft Icing Phenomena 548
18.2 Impact Icing Pertinent to Aircraft Icing vs. Conventional Frosting or Static Icing 551
18.3 State-of-the-Art Bio-Inspired Icephobic Coatings 553
18.3.1 Superhydrophobic Surfaces with Micro-/Nano-Scale Textures 555
18.3.2 Slippery Liquid-Infused Porous Surfaces 557
18.3.3 Icephobic Soft Materials with Ultra-Low Ice Adhesion Strength and Good Mechanical Durability 558
18.4 Comparison of Ice Adhesion Strengths of Different Bio-Inspired Icephobic Coatings 560
18.5 Durability of the Bio-Inspired Icephobic Coatings under High-Speed Droplet Impacting 562
18.6 Icing Tunnel Testing to Evaluate the Effectiveness of the Icephobic Coatings for Impact Icing Mitigation 566
18.7 Summary 569
Acknowledgments 571
References 571
19 Effect of and Protection from Ice Accretion on Aircraft 577
Zhenlong Wu and Qiang Wang
Glossary 577
19.1 Introduction 578
19.2 Fundamental Icing Parameters 579
19.2.1 Droplet Diameter 579
19.2.2 Liquid Water Content 580
19.2.3 Ambient Icing Temperature 581
19.3 Types of Ice on Aircraft 581
19.3.1 Rime Ice 581
19.3.2 Glaze Ice 582
19.3.3 Mixed Ice 583
19.4 Aircraft Icing Effects 584
19.4.1 Iced Aerodynamics 584
19.4.1.1 Drag Rise 584
19.4.1.2 Lift Reduction 586
19.4.1.3 Moment Variation 589
19.4.1.4 Separation Bubble Formation 590
19.4.1.5 Boundary Layer Thickening 592
19.4.2 Iced Flight Mechanics 594
19.4.2.1 Flight Performance Disruption 594
19.4.2.2 Stability and Control Degradation 596
19.5 Sensing of and Protection from Aircraft Icing 596
19.5.1 Sensing of Ice Accretion 596
19.5.2 De-Icing and Anti-Icing 598
19.5.3 Envelope Protection 599
19.5.4 Control Reconfiguration 601
19.6 Summary 603
Funding and Acknowledgement 603
References 603
20 Numerical Modeling and Its Application to Inflight Icing 607
Kwanjung Yee
20.1 Introduction 608
20.2 Aircraft Icing 609
20.2.1 Icing Environment 609
20.2.1.1 Cloud Formation 609
20.2.1.2 Cloud Classification 609
20.2.1.3 Icing Cloud 613
20.2.1.4 Icing Envelope 615
20.2.2 Icing Mechanism 617
20.2.2.1 Fundamentals of Icing 617
20.2.2.2 Characterization of Ice Shape 620
20.2.2.3 Critical Issues in Icing Physics 621
20.3 Numerical Technique for Inflight Icing 625
20.3.1 Composition of the Inflight Icing Code 626
20.3.2 Flow Analysis Solver 628
20.3.2.1 Inviscid Flow Solver 628
20.3.2.2 Reynolds-Averaged Navier-Stokes (RANS) Equation 631
20.3.3 Droplet Trajectory Module 635
20.3.3.1 Lagrangian Approach 635
20.3.3.2 Eulerian Approach 637
20.3.4 Thermodynamic Module 639
20.3.4.1 Messinger Model 639
20.3.4.2 Extended Messinger Model (Stefan Equation) 641
20.3.4.3 Shallow Water Icing Model (SWIM) 642
20.3.5 Ice Growth Module 644
20.3.6 Application of the Numerical Simulation 645
20.3.6.1 2D Airfoil 646
20.3.6.2 3D DLR-F6 Configuration 647
20.3.6.3 Rotorcraft Fuselage 649
20.4 Numerical Simulation of Icing Protection System (IPS) 651
20.4.1 IPS 651
20.4.2 Simulation for IPS 653
20.4.3 Thermal IPS Simulation Analysis 655
20.4.3.1 Electro-Thermal IPS Simulation 655
20.4.3.2 Water Film Analysis 656
20.5 Numerical Issues in the Inflight Icing Code 658
20.5.1 Analysis of the Surface Roughness 658
20.5.2 Analysis of the Transition in the Boundary Layer Problem 659
20.5.3 Analysis of the Rotor Blade Icing Problem 660
20.5.4 Analysis of the Uncertainty Qualification (UQ) 661
20.6 Summary 662
References 663
1
Factors Influencing the Formation, Adhesion, and Friction of Ice
Michael J. Wood and Anne-Marie Kietzig*
Department of Chemical Engineering, McGill University, Montreal, Canada
Abstract
Humans have faced the challenges and opportunities afforded by ice accumulation throughout our collective history. From the icing over of hunting plains to the accretion of ice on aeroplanes, the challenge of frozen water has shaped us as a species. In many ways, overcoming the challenge of surface ice accumulation is inextricably linked to human modernity. We have reached a point in engineering history where some of the most important unanswered questions cannot be fully resolved without the management and prevention of surface ice. These engineering challenges include: the complete implementation of renewable energy sources such as photovoltaic panels, wind turbines, and the requisite electrical transmission lines, the ushering in of the age of environmentally-friendly air travel, including the elimination of de-icing fluids, and the introduction of fully autonomous vehicles which will require sensors that are perpetually free of surface ice and roadways that are reliably ice free.
This chapter begins with a brief history of ice on Earth, followed by an overview of how humans have faced ice accumulation in the past and how advances in technology during the first two Industrial Revolutions have facilitated our understanding of ice formation. Next, we discuss the ice formation process in terms of embryo nucleation. This is followed by a discussion of the factors influencing ice adhesion, specifically the important relationship between surface morphology and ice adhesion strength. Finally, the origins of ice's low friction is discussed in the last section.
Keywords: Surface icing, ice on earth, wetting, ice ages, anti-icing technology, ice formation, ice nucleation, ice growth, ice adhesion, ice friction
1.1 A Brief History of Man and Ice
1.1.1 Ice on Earth
Planet Earth is in a constant, albeit slowly, changing state. In the 4.5 billion years since its formation, the climate of Earth has gone through many fluctuations in which there have been periods of more or less ice accumulation. Upon formation, during the Hadean Eon, young planet Earth was completely molten and had frequent collisions with other bodies in the primordial solar system [1]. Many of these colliding bodies were "planetary embryos" which were carriers of water, thought to have originated from the outer asteroid belt [2]. The accumulation of water around the molten blob that was Earth allowed for cooling to occur and a solid crust to form approximately 4.4 billion years ago. One of the collisions with another celestial body caused the formation of the Moon, and in the same process created Earth's early CO2- and water vapour-rich atmosphere. The high pressure of this young atmosphere allowed for the first time liquid water oceans to exist on Earth, despite the estimated surface temperature of 230°C [3].
Single-cellular life emerged in Earth's oceans approximately 4 billion years ago, marking the start of the Archean Eon [4]. Oceanic cyanobacteria, the first single-celled organisms capable of photosynthesis, appeared approximately 3.5 billion years ago and started producing oxygen as a waste product. The oxygen produced through photosynthesis was readily captured chemically by dissolved iron until approximately 2.4 billion years ago when these oxygen stores became filled, at which point atmospheric oxygen appeared for the first time [5]. This Eon, known as the Proterozoic, also saw volcanic activity diminish which lessened the levels of atmospheric CO2. The lowered CO2 and increased O2 concentrations resulted in a weakened greenhouse effect, leading to the Huronian glaciation [6]. This marks the first time that water existed as a solid on Earth. The approximately 300 million year long event was severe, with the entire planet being frozen over in what has been termed "snowball Earth". The Huronian Ice Age was one of the main contributing factors to planet Earth's first mass extinction [6, 7].
Earth's temperature rebounded approximately 2.1 billion years ago, allowing for the first Eukaryotic cells to form. This was followed by the emergence of multicellular organisms approximately 1.6 billion years ago [8]. As multicellular organisms began to grow larger, and more complex, their death (and subsequent sinking to the seabed) is hypothesized to have served as a sequestration of CO2 [9, 10]. The sequestration of CO2 caused the onset of the Cryogenian period 720 million years ago, a period which included the longest known ice ages: the Sturtian and Marinoan glaciations [11]. The post-Cryogenian Earth has seen the evolution of Molluscs and Anthropods, in what has become known as the Cambrian Explosion due to the gigantic number and diversity of the forms of life introduced [12, 13]. The Andean-Saharan glaciation marked the next major extinction event on Earth, approximately 450 million years ago and lasted about 30 million years [14]. The end of the Andean-Saharan ice age ushered in the evolution of the first Tetrapoda, Earth's first land animals as well as an explosion in the number of land plants [15, 16]. The huge number of land plants greatly increased the level of atmospheric oxygen, and decreased the level of atmospheric CO2, leading to another period of a weakened greenhouse effect. Thus started the Late Paleozoic Ice Age approximately 360 million years ago which would last approximately 100 million years [17].
The rebound in global temperatures following the end of the Late Paleozoic Ice Age saw the introduction of large land animals, most notably the Dinosaurs in the late Triassic period approximately 240 million years ago [18]. Following the extinction of the Dinosaurs about 66 million years ago, mammals, birds and flowers evolved, again affecting the level of atmospheric CO2. The decreased greenhouse effect of the present time started approximately 2.6 million years ago, leading to what is called the Quaternary (or Current) Ice Age [19]. Periodic changes in the Earth's orbit around the sun during this glaciation has resulted in characteristic interglacial (or warm) events [20]. The latest such retreat of the ice sheets 12000 years ago has been called the Holocene Epoch, and has allowed humans to inhabit northern latitudes [21].
1.1.2 Man is Carved of Ice
It is evident from Figure 1.1 that life and ice on Earth have had a symbiotic relationship. The emergence of new life on the planet has contributed to changes in the atmosphere, lessening the greenhouse effect, and leading to periods of glaciation (including the very first appearance of ice on the planet). The evolutionary selection pressures of drops in global temperature led to mass extinction events where the only organisms that survived were those fit to live in the cold. The cold climate selection pressures, among many others, led to the evolutionary emergence of more complex Eukaryotic cells, and eventually multicellular organisms which in death sequestered CO2, leading to more glaciation. This cycle continued with the introduction of land plants and animals, Dinosaurs, mammals, birds and flowers, until the current geologic period of the Earth - the Quaternary -was reached.
Figure 1.1 A geologic timeline of the Earth shows the symbiotic relationship between life and ice on the planet. The inset of the past 9 million years shows the specific relationship between glaciation of Earth (through oxygen-18 isotope measurements) and human evolution. d18O data is taken from [22]. bya and mya denote billons of years ago and millions of years ago, respectively.
Climate fluctuations continue to affect the evolution of living things; the evolution of living things continues to affect the climate. In fact, the climatic conditions in the Quaternary Ice Age, including those which present the conditions for ice formation, have shaped the selection pressures experienced by early humans, and thus human evolution [23]. Although the first Primates evolved approximately 60 million years ago, the earliest Apes appeared on Earth approximately 20 million years ago [24]. As Earth entered the Neogenic and Quaternary periods, the characteristic dramatic climatic fluctuations of these geological time periods ushered in the evolution of the first Homininae, the tribe including Gorillas, Chimpanzees and Humans [25]. Earth's climate throughout the Pliocene (beginning approximately 5.3 million years ago), Pleistocene (beginning 2.5 million years ago), and Holocene (beginning 12000 years ago) epochs has trended towards not only a colder more glaciated world, but also increased amplitude and frequency between cool and warm periods, as determined through oxygen isotope analysis of ice core samples [22]. Many of the major developments in hominin evolution have been coincident with the intensification of Northern Hemisphere glaciation, as shown in Figure 1.1 [26].
Adaptations to the increasingly unpredictable and unstable environments of the late Neogene and Quaternary periods might in fact be part of what it means to become a human in the Darwinian sense [26, 27]. The morphological and behavioural traits of terrestriality, bipedalism, dietary flexibility, tool use, omnivory, large brains, long-distance migrations, and...
